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Datta R, Heaster TM, Sharick JT, Gillette AA, Skala MC. Fluorescence lifetime imaging microscopy: fundamentals and advances in instrumentation, analysis, and applications. JOURNAL OF BIOMEDICAL OPTICS 2020; 25:1-43. [PMID: 32406215 PMCID: PMC7219965 DOI: 10.1117/1.jbo.25.7.071203] [Citation(s) in RCA: 270] [Impact Index Per Article: 67.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/06/2020] [Accepted: 04/24/2020] [Indexed: 05/18/2023]
Abstract
SIGNIFICANCE Fluorescence lifetime imaging microscopy (FLIM) is a powerful technique to distinguish the unique molecular environment of fluorophores. FLIM measures the time a fluorophore remains in an excited state before emitting a photon, and detects molecular variations of fluorophores that are not apparent with spectral techniques alone. FLIM is sensitive to multiple biomedical processes including disease progression and drug efficacy. AIM We provide an overview of FLIM principles, instrumentation, and analysis while highlighting the latest developments and biological applications. APPROACH This review covers FLIM principles and theory, including advantages over intensity-based fluorescence measurements. Fundamentals of FLIM instrumentation in time- and frequency-domains are summarized, along with recent developments. Image segmentation and analysis strategies that quantify spatial and molecular features of cellular heterogeneity are reviewed. Finally, representative applications are provided including high-resolution FLIM of cell- and organelle-level molecular changes, use of exogenous and endogenous fluorophores, and imaging protein-protein interactions with Förster resonance energy transfer (FRET). Advantages and limitations of FLIM are also discussed. CONCLUSIONS FLIM is advantageous for probing molecular environments of fluorophores to inform on fluorophore behavior that cannot be elucidated with intensity measurements alone. Development of FLIM technologies, analysis, and applications will further advance biological research and clinical assessments.
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Affiliation(s)
- Rupsa Datta
- Morgridge Institute for Research, Madison, Wisconsin, United States
| | - Tiffany M. Heaster
- Morgridge Institute for Research, Madison, Wisconsin, United States
- University of Wisconsin, Department of Biomedical Engineering, Madison, Wisconsin, United States
| | - Joe T. Sharick
- Morgridge Institute for Research, Madison, Wisconsin, United States
| | - Amani A. Gillette
- Morgridge Institute for Research, Madison, Wisconsin, United States
- University of Wisconsin, Department of Biomedical Engineering, Madison, Wisconsin, United States
| | - Melissa C. Skala
- Morgridge Institute for Research, Madison, Wisconsin, United States
- University of Wisconsin, Department of Biomedical Engineering, Madison, Wisconsin, United States
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2
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Schneckenburger H. Förster resonance energy transfer-what can we learn and how can we use it? Methods Appl Fluoresc 2019; 8:013001. [PMID: 31715588 DOI: 10.1088/2050-6120/ab56e1] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The present manuscript gives a short overview on Förster Resonance Energy Transfer (FRET) of molecular interactions in the nanometre range. First, its principle is described and a short historical overview is given. Subsequently some principal methods and applications of FRET sensing and imaging are described (with some emphasis on fluorescence lifetime imaging, FLIM), and finally two innovative FRET techniques are presented in more detail. Applications are focused on measurements of living cells.
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3
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Leben R, Köhler M, Radbruch H, Hauser AE, Niesner RA. Systematic Enzyme Mapping of Cellular Metabolism by Phasor-Analyzed Label-Free NAD(P)H Fluorescence Lifetime Imaging. Int J Mol Sci 2019; 20:ijms20225565. [PMID: 31703416 PMCID: PMC6887798 DOI: 10.3390/ijms20225565] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2019] [Accepted: 11/04/2019] [Indexed: 12/15/2022] Open
Abstract
In the past years, cellular metabolism of the immune system experienced a revival, as it has become clear that it is not merely responsible for the cellular energy supply, but also impacts on many signaling pathways and, thus, on diverse cellular functions. Label-free fluorescence lifetime imaging of the ubiquitous coenzymes NADH and NADPH (NAD(P)H-FLIM) makes it possible to monitor cellular metabolism in living cells and tissues and has already been applied to study metabolic changes both under physiologic and pathologic conditions. However, due to the complex distribution of NAD(P)H-dependent enzymes in cells, whose distribution continuously changes over time, a thorough interpretation of NAD(P)H-FLIM results, in particular, resolving the contribution of various enzymes to the overall metabolic activity, remains challenging. We developed a systematic framework based on angle similarities of the phase vectors and their length to analyze NAD(P)H-FLIM data of cells and tissues based on a generally valid reference system of highly abundant NAD(P)H-dependent enzymes in cells. By using our analysis framework, we retrieve information not only about the overall metabolic activity, i.e., the fraction of free to enzyme-bound NAD(P)H, but also identified the enzymes predominantly active within the sample at a certain time point with subcellular resolution. We verified the performance of the approach by applying NAD(P)H-FLIM on a stromal-like cell line and identified a different group of enzymes that were active in the cell nuclei as compared to the cytoplasm. As the systematic phasor-based analysis framework of label-free NAD(P)H-FLIM can be applied both in vitro and in vivo, it retains the unique power to enable dynamic enzyme-based metabolic investigations, at subcellular resolution, in genuine environments.
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Affiliation(s)
- Ruth Leben
- Biophysical Analytics, Deutsches Rheuma-Forschungszentrum (DRFZ), 10117 Berlin, Germany;
- Dynamic and Functional in vivo Imaging, Freie Universität Berlin, 14163 Berlin, Germany
- Correspondence: (R.L.); (R.A.N.); Tel.: +49-30-2846-0674 (R.L.); +49-30-2846-0708 (R.A.N.)
| | - Markus Köhler
- Biophysical Analytics, Deutsches Rheuma-Forschungszentrum (DRFZ), 10117 Berlin, Germany;
- Dynamic and Functional in vivo Imaging, Freie Universität Berlin, 14163 Berlin, Germany
| | - Helena Radbruch
- Institute for Neuropathology, Charité–Universitätsmedizin Berlin, 10117 Berlin, Germany;
| | - Anja E. Hauser
- Immune Dynamics, Deutsches Rheuma-Forschungszentrum (DRFZ), 10117 Berlin, Germany;
- Immunodynamics and Intravital Microscopy, Charité–Universitätsmedizin Berlin, 10117 Berlin, Germany
| | - Raluca A. Niesner
- Biophysical Analytics, Deutsches Rheuma-Forschungszentrum (DRFZ), 10117 Berlin, Germany;
- Dynamic and Functional in vivo Imaging, Freie Universität Berlin, 14163 Berlin, Germany
- Correspondence: (R.L.); (R.A.N.); Tel.: +49-30-2846-0674 (R.L.); +49-30-2846-0708 (R.A.N.)
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Chen H, Ma N, Kagawa K, Kawahito S, Digman M, Gratton E. Widefield multifrequency fluorescence lifetime imaging using a two-tap complementary metal-oxide semiconductor camera with lateral electric field charge modulators. JOURNAL OF BIOPHOTONICS 2019; 12:e201800223. [PMID: 30421535 DOI: 10.1002/jbio.201800223] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2018] [Revised: 10/30/2018] [Accepted: 11/09/2018] [Indexed: 06/09/2023]
Abstract
Widefield frequency-domain fluorescence lifetime imaging microscopy (FD-FLIM) measures the fluorescence lifetime of entire images in a fast and efficient manner. We report a widefield FD-FLIM system based on a complementary metal-oxide semiconductor camera equipped with two-tap true correlated double sampling lock-in pixels and lateral electric field charge modulators. Owing to the fast intrinsic response and modulation of the camera, our system allows parallel multifrequency FLIM in one measurement via fast Fourier transform. We demonstrate that at a fundamental frequency of 20 MHz, 31-harmonics can be measured with 64 phase images per laser repetition period. As a proof of principle, we analyzed cells transfected with Cerulean and with a construct of Cerulean-Venus that shows Förster Resonance Energy Transfer at different modulation frequencies. We also tracked the temperature change of living cells via the fluorescence lifetime of Rhodamine B at different frequencies. These results indicate that our widefield multifrequency FD-FLIM system is a valuable tool in the biomedical field.
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Affiliation(s)
- Hongtao Chen
- Laboratory for Fluorescence Dynamics, Department of Biomedical Engineering, University of California, Irvine, California
| | - Ning Ma
- Laboratory for Fluorescence Dynamics, Department of Biomedical Engineering, University of California, Irvine, California
| | - Keiichiro Kagawa
- Research Institute of Electronics, Shizuoka University, Hamamatsu, Shizuoka, Japan
| | - Shoji Kawahito
- Research Institute of Electronics, Shizuoka University, Hamamatsu, Shizuoka, Japan
| | - Michelle Digman
- Laboratory for Fluorescence Dynamics, Department of Biomedical Engineering, University of California, Irvine, California
| | - Enrico Gratton
- Laboratory for Fluorescence Dynamics, Department of Biomedical Engineering, University of California, Irvine, California
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5
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Dake F, Taki Y. Time-domain fluorescence lifetime imaging by nonlinear fluorescence microscopy constructed of a pump-probe setup with two-wavelength laser pulses. APPLIED OPTICS 2018; 57:757-762. [PMID: 29400744 DOI: 10.1364/ao.57.000757] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/10/2017] [Accepted: 12/25/2017] [Indexed: 06/07/2023]
Abstract
We propose a time-domain approach for fluorescence lifetime measurements using nonlinear fluorescence microscopy constructed of a pump-probe setup with two-wavelength laser pulses. Nonlinear fluorescence signals generated by fluorescence reduction due to stimulated emission were detectable through a lock-in technique. Changing the time delay between the two-wavelength pulses enables acquisition of a time-resolved nonlinear fluorescence signal, which directly reflects the fluorescence lifetime of the sample and is thus applicable to fluorescence lifetime imaging. We also quantitatively demonstrate that nonlinear fluorescence microscopy possesses better optical resolution than conventional laser-scanning fluorescence microscopy. Experimental trials indicate that straightforward fluorescence lifetime imaging with high optical resolution is readily available.
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Yahav G, Barnoy E, Roth N, Turgeman L, Fixler D. Reference-independent wide field fluorescence lifetime measurements using Frequency-Domain (FD) technique based on phase and amplitude crossing point. JOURNAL OF BIOPHOTONICS 2017; 10:1198-1207. [PMID: 27774782 DOI: 10.1002/jbio.201600220] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2016] [Revised: 09/29/2016] [Accepted: 09/30/2016] [Indexed: 06/06/2023]
Abstract
Fluorescence lifetime imaging microscopy (FLIM) is an essential tool in many scientific fields such as biology and medicine thanks to the known advantages of the fluorescence lifetime (FLT) over the classical fluorescence intensity (FI). However, the frequency domain (FD) FLIM technique suffers from its strong dependence on the reference and its compliance to the sample. In this paper, we suggest a new way to calculate the FLT by using the crossing point (CRPO) between the modulation and phase FLTs measured over several light emitting diode (LED) DC currents values instead of either method alone. This new technique was validated by measuring homogeneous substances with known FLT, where the CRPO appears to be the optimal measuring point. Furthermore, the CRPO method was applied in heterogeneous samples. It was found that the CRPO in known mixed solutions is the weighted average of the used solutions. While measuring B16 and lymphocyte cells, the CRPO of the DAPI compound in single FLT regions was measured at 3.5 ± 0.06 ns and at 2.83 ± 0.07 ns, respectively, both of which match previous reports and multi-frequency analyses. This paper suggests the CRPO as a new method to extract the FLT in problematic cases such as high MCP gains and heterogeneous environments. In traditional FD FLIM measurements, the variation in phase angle and modulation are measured. By measuring over varying DC currents, another variation is detected in the FLT determined through the phase and modulation methods, with the CRPO indicating the true FLT.
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Affiliation(s)
- Gilad Yahav
- Faculty of Engineering and the Institute of Nanotechnology and Advanced Materials, Bar Ilan University, 5290002, Ramat Gan, Israel
| | - Eran Barnoy
- Faculty of Engineering and the Institute of Nanotechnology and Advanced Materials, Bar Ilan University, 5290002, Ramat Gan, Israel
| | - Nir Roth
- Faculty of Engineering and the Institute of Nanotechnology and Advanced Materials, Bar Ilan University, 5290002, Ramat Gan, Israel
| | - Lior Turgeman
- Joseph M. Katz Graduate School of Business, University of Pittsburgh, Roberto Clemente Dr, PA, 15260, Pittsburgh, USA
| | - Dror Fixler
- Faculty of Engineering and the Institute of Nanotechnology and Advanced Materials, Bar Ilan University, 5290002, Ramat Gan, Israel
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7
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Fereidouni F, Gorpas D, Ma D, Fatakdawala H, Marcu L. Rapid fluorescence lifetime estimation with modified phasor approach and Laguerre deconvolution: a comparative study. Methods Appl Fluoresc 2017; 5:035003. [PMID: 28644150 PMCID: PMC6043162 DOI: 10.1088/2050-6120/aa7b62] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Fluorescence lifetime imaging has been shown to serve as a valuable tool for interrogating and diagnosis of biological tissue at a mesoscopic level. The ability to analyze fluorescence decay curves to extract lifetime values in real-time is crucial for clinical translation and applications such as tumor margin delineation or intracoronary imaging of atherosclerotic plaques. In this work, we compare the performance of two popular non-parametric (fit-free) methods for determining lifetime values from fluorescence decays in real-time-the Phasor approach and Laguerre deconvolution. We demonstrate results from simulated and experimental data to compare the accuracy and speed of both methods and their dependence on noise and model parameters.
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Affiliation(s)
- Farzad Fereidouni
- Department of Pathology and Laboratory Medicine, 4400 V Street, CA 95817, United States of America
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8
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Lin J, Liu Y, Suo J, Dai Q. Frequency-Domain Transient Imaging. IEEE TRANSACTIONS ON PATTERN ANALYSIS AND MACHINE INTELLIGENCE 2017; 39:937-950. [PMID: 28113541 DOI: 10.1109/tpami.2016.2560814] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
A transient image is the optical impulse response of a scene, which also visualizes the propagation of light during an ultra-short time interval. In contrast to the previous transient imaging which samples in the time domain using an ultra-fast imaging system, this paper proposes transient imaging in the frequency domain using a multi-frequency time-of-flight (ToF) camera. Our analysis reveals the Fourier relationship between transient images and the measurements of a multi-frequency ToF camera, and identifies the causes of the systematic error-non-sinusoidal and frequency-varying waveforms and limited frequency range of the modulation signal. Based on the analysis we propose a novel framework of frequency-domain transient imaging. By removing the systematic error and exploiting the harmonic components inside the measurements, we achieves high quality reconstruction results. Moreover, our technique significantly reduces the computational cost of ToF camera based transient image reconstruction, especially reduces the memory usage, such that it is feasible for the reconstruction of transient images at extremely small time steps. The effectiveness of frequency-domain transient imaging is tested on synthetic data, real data from the web, and real data acquired by our prototype camera.
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9
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Chen H, Holst G, Gratton E. Modulated CMOS camera for fluorescence lifetime microscopy. Microsc Res Tech 2015; 78:1075-81. [PMID: 26500051 DOI: 10.1002/jemt.22587] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2015] [Accepted: 09/21/2015] [Indexed: 11/11/2022]
Abstract
Widefield frequency-domain fluorescence lifetime imaging microscopy (FD-FLIM) is a fast and accurate method to measure the fluorescence lifetime of entire images. However, the complexity and high costs involved in construction of such a system limit the extensive use of this technique. PCO AG recently released the first luminescence lifetime imaging camera based on a high frequency modulated CMOS image sensor, QMFLIM2. Here we tested and provide operational procedures to calibrate the camera and to improve the accuracy using corrections necessary for image analysis. With its flexible input/output options, we are able to use a modulated laser diode or a 20 MHz pulsed white supercontinuum laser as the light source. The output of the camera consists of a stack of modulated images that can be analyzed by the SimFCS software using the phasor approach. The nonuniform system response across the image sensor must be calibrated at the pixel level. This pixel calibration is crucial and needed for every camera settings, e.g. modulation frequency and exposure time. A significant dependency of the modulation signal on the intensity was also observed and hence an additional calibration is needed for each pixel depending on the pixel intensity level. These corrections are important not only for the fundamental frequency, but also for the higher harmonics when using the pulsed supercontinuum laser. With these post data acquisition corrections, the PCO CMOS-FLIM camera can be used for various biomedical applications requiring a large frame and high speed acquisition.
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Affiliation(s)
- Hongtao Chen
- Laboratory for Fluorescence Dynamics, Department of Biomedical Engineering University of California, Irvine, California
| | | | - Enrico Gratton
- Laboratory for Fluorescence Dynamics, Department of Biomedical Engineering University of California, Irvine, California
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10
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Roudot P, Kervrann C, Blouin CM, Waharte F. Lifetime estimation of moving subcellular objects in frequency-domain fluorescence lifetime imaging microscopy. JOURNAL OF THE OPTICAL SOCIETY OF AMERICA. A, OPTICS, IMAGE SCIENCE, AND VISION 2015; 32:1821-1835. [PMID: 26479936 DOI: 10.1364/josaa.32.001821] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Fluorescence lifetime is usually defined as the average nanosecond-scale delay between excitation and emission of fluorescence. It has been established that lifetime measurements yield numerous indications on cellular processes such as interprotein and intraprotein mechanisms through fluorescent tagging and Förster resonance energy transfer. In this area, frequency-domain fluorescence lifetime imaging microscopy is particularly appropriate to probe a sample noninvasively and quantify these interactions in living cells. The aim is then to measure the fluorescence lifetime in the sample at each location in space from fluorescence variations observed in a temporal sequence of images obtained by phase modulation of the detection signal. This leads to a sensitivity of lifetime determination to other sources of fluorescence variations such as intracellular motion. In this paper, we propose a robust statistical method for lifetime estimation for both background and small moving structures with a focus on intracellular vesicle trafficking.
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12
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Chan JCK, Diebold ED, Buckley BW, Mao S, Akbari N, Jalali B. Digitally synthesized beat frequency-multiplexed fluorescence lifetime spectroscopy. BIOMEDICAL OPTICS EXPRESS 2014; 5:4428-36. [PMID: 25574449 PMCID: PMC4285616 DOI: 10.1364/boe.5.004428] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2014] [Revised: 09/24/2014] [Accepted: 10/25/2014] [Indexed: 05/02/2023]
Abstract
Frequency domain fluorescence lifetime imaging is a powerful technique that enables the observation of subtle changes in the molecular environment of a fluorescent probe. This technique works by measuring the phase delay between the optical emission and excitation of fluorophores as a function of modulation frequency. However, high-resolution measurements are time consuming, as the excitation modulation frequency must be swept, and faster low-resolution measurements at a single frequency are prone to large errors. Here, we present a low cost optical system for applications in real-time confocal lifetime imaging, which measures the phase vs. frequency spectrum without sweeping. Deemed Lifetime Imaging using Frequency-multiplexed Excitation (LIFE), this technique uses a digitally-synthesized radio frequency comb to drive an acousto-optic deflector, operated in a cat's-eye configuration, to produce a single laser excitation beam modulated at multiple beat frequencies. We demonstrate simultaneous fluorescence lifetime measurements at 10 frequencies over a bandwidth of 48 MHz, enabling high speed frequency domain lifetime analysis of single- and multi-component sample mixtures.
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Affiliation(s)
- Jacky C. K. Chan
- Departments of Electrical Engineering, University of California, Los Angeles, CA 90095,
USA
| | - Eric D. Diebold
- Departments of Electrical Engineering, University of California, Los Angeles, CA 90095,
USA
- Department of Bioengineering, University of California, Los Angeles, CA 90095,
USA
| | - Brandon W. Buckley
- Departments of Electrical Engineering, University of California, Los Angeles, CA 90095,
USA
| | - Sien Mao
- Departments of Electrical Engineering, University of California, Los Angeles, CA 90095,
USA
| | - Najva Akbari
- Departments of Electrical Engineering, University of California, Los Angeles, CA 90095,
USA
| | - Bahram Jalali
- Departments of Electrical Engineering, University of California, Los Angeles, CA 90095,
USA
- Department of Bioengineering, University of California, Los Angeles, CA 90095,
USA
- Department of Surgery, David Geffen School of Medicine, University of California, Los Angeles, CA 90095,
USA
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Zhao M, Li Y, Peng L. FPGA-based multi-channel fluorescence lifetime analysis of Fourier multiplexed frequency-sweeping lifetime imaging. OPTICS EXPRESS 2014; 22:23073-85. [PMID: 25321778 PMCID: PMC4247184 DOI: 10.1364/oe.22.023073] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2014] [Revised: 08/26/2014] [Accepted: 08/27/2014] [Indexed: 05/02/2023]
Abstract
We report a fast non-iterative lifetime data analysis method for the Fourier multiplexed frequency-sweeping confocal FLIM (Fm-FLIM) system [Opt. Express 22, 10221 (2014)]. The new method, named R-method, allows fast multi-channel lifetime image analysis in the system's FPGA data processing board. Experimental tests proved that the performance of the R-method is equivalent to that of single-exponential iterative fitting, and its sensitivity is well suited for time-lapse FLIM-FRET imaging of live cells, for example cyclic adenosine monophosphate (cAMP) level imaging with GFP-Epac-mCherry sensors. With the R-method and its FPGA implementation, multi-channel lifetime images can now be generated in real time on the multi-channel frequency-sweeping FLIM system, and live readout of FRET sensors can be performed during time-lapse imaging.
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Affiliation(s)
- Ming Zhao
- College of Optical Sciences, the University of Arizona, 1630 East University Blvd., Tucson, AZ 85721,
USA
| | - Yu Li
- College of Optical Sciences, the University of Arizona, 1630 East University Blvd., Tucson, AZ 85721,
USA
| | - Leilei Peng
- College of Optical Sciences, the University of Arizona, 1630 East University Blvd., Tucson, AZ 85721,
USA
- Molecular and Cellular Biology, the University of Arizona, 1007 E. Lowell St., Tucson, AZ 85721,
USA
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Cicchi R, Vogler N, Kapsokalyvas D, Dietzek B, Popp J, Pavone FS. From molecular structure to tissue architecture: collagen organization probed by SHG microscopy. JOURNAL OF BIOPHOTONICS 2013; 6:129-42. [PMID: 22791562 DOI: 10.1002/jbio.201200092] [Citation(s) in RCA: 119] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/18/2012] [Revised: 06/15/2012] [Accepted: 06/15/2012] [Indexed: 05/11/2023]
Abstract
Second-harmonic generation (SHG) microscopy is a fantastic tool for imaging collagen and probing its hierarchical organization from molecular scale up to tissue architectural level. In fact, SHG combines the advantages of a non-linear microscopy approach with a coherent modality able to probe molecular organization. In this manuscript we review the physical concepts describing SHG from collagen, highlighting how this optical process allows to probe structures ranging from molecular sizes to tissue architecture, through image pattern analysis and scoring methods. Starting from the description of the most relevant approaches employing SHG polarization anisotropy and forward - backward SHG detection, we then focus on the most relevant methods for imaging and characterizing collagen organization in tissues through image pattern analysis methods, highlighting advantages and limitations of the methods applied to tissue imaging and to potential clinical applications.
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Affiliation(s)
- Riccardo Cicchi
- European Laboratory for Non-linear Spectroscopy LENS, Via Nello Carrara 1, 50019 Sesto Fiorentino, Italy.
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15
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Chen H, Gratton E. A practical implementation of multifrequency widefield frequency-domain fluorescence lifetime imaging microscopy. Microsc Res Tech 2013; 76:282-9. [PMID: 23296945 DOI: 10.1002/jemt.22165] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2012] [Accepted: 11/26/2012] [Indexed: 11/10/2022]
Abstract
Widefield frequency-domain fluorescence lifetime imaging microscopy (FD-FLIM) is a fast and accurate method to measure the fluorescence lifetime, especially in kinetic studies in biomedical researches. However, the small range of modulation frequencies available in commercial instruments makes this technique limited in its applications. Herein, we describe a practical implementation of multifrequency widefield FD-FLIM using a pulsed supercontinuum laser and a direct digital synthesizer. In this instrument we use a pulse to modulate the image intensifier rather than the more conventional sine-wave modulation. This allows parallel multifrequency FLIM measurement using the Fast Fourier Transform and the cross-correlation technique, which permits precise and simultaneous isolation of individual frequencies. In addition, the pulse modulation at the cathode of image intensifier restores the loss of optical resolution caused by the defocusing effect when the cathode is sinusoidally modulated. Furthermore, in our implementation of this technique, data can be graphically analyzed by the phasor method while data are acquired, which allows easy fit-free lifetime analysis of FLIM images. Here, our measurements of standard fluorescent samples and a Föster resonance energy transfer pair demonstrate that the widefield multifrequency FLIM system is a valuable and simple tool in fluorescence imaging studies.
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Affiliation(s)
- Hongtao Chen
- Laboratory for Fluorescence Dynamics, Department of Biomedical Engineering, University of California, Irvine, California, USA
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From FRET Imaging to Practical Methodology for Kinase Activity Sensing in Living Cells. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2013; 113:145-216. [DOI: 10.1016/b978-0-12-386932-6.00005-3] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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17
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Gidon A, Bardin S, Cinquin B, Boulanger J, Waharte F, Heliot L, Salle H, Hanau D, Kervrann C, Goud B, Salamero J. A Rab11A/Myosin Vb/Rab11-FIP2 Complex Frames Two Late Recycling Steps of Langerin from the ERC to the Plasma Membrane. Traffic 2012; 13:815-33. [DOI: 10.1111/j.1600-0854.2012.01354.x] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2011] [Revised: 03/13/2012] [Accepted: 03/15/2012] [Indexed: 01/29/2023]
Affiliation(s)
- Alexandre Gidon
- UMR 144, Molecular Mechanisms of Intracellular Transport Laboratory; CNRS-Institut Curie; 26 rue d'Ulm; 75248; Paris cedex 05; France
| | - Sabine Bardin
- UMR 144, Molecular Mechanisms of Intracellular Transport Laboratory; CNRS-Institut Curie; 26 rue d'Ulm; 75248; Paris cedex 05; France
| | | | - Jerome Boulanger
- Cell and Tissue Imaging Facility, PICT-IBiSA & Nikon Imaging Center; UMR 144 CNRS-Institut Curie; 26 rue d'Ulm; 75248; Paris cedex 05; France
| | - François Waharte
- Cell and Tissue Imaging Facility, PICT-IBiSA & Nikon Imaging Center; UMR 144 CNRS-Institut Curie; 26 rue d'Ulm; 75248; Paris cedex 05; France
| | - Laurent Heliot
- Interdisciplinary Research Institute, Molecular Dynamics and Interaction in Living Cell; 59658; Villeneuve d'Ascq; France
| | - Henri Salle
- INSERM U 725, Biology of Human Dendritic Cells; Strasbourg; France
| | - Daniel Hanau
- INSERM U 725, Biology of Human Dendritic Cells; Strasbourg; France
| | - Charles Kervrann
- INRIA Rennes - Bretagne Atlantique. Team SERPICO; Campus de Beaulieu; 35042; Rennes cedex; France
| | - Bruno Goud
- UMR 144, Molecular Mechanisms of Intracellular Transport Laboratory; CNRS-Institut Curie; 26 rue d'Ulm; 75248; Paris cedex 05; France
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Whole-object fluorescence lifetime setup for efficient non-imaging quantitative intracellular fluorophore measurements. J Fluoresc 2012; 22:875-82. [PMID: 22258423 DOI: 10.1007/s10895-011-1025-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2011] [Accepted: 11/21/2011] [Indexed: 10/14/2022]
Abstract
In the present study we introduce a Whole-Object Fluorescence Life Time (wo-FLT) measurement approach for ease and a relatively inexpensive method of tracing alterations in intracellular fluorophore distribution and in the physical-chemical features of the microenvironments hosting the fluorophore. Two common fluorophores, Rhodamine 123 and Acridine Orange, were used to stain U937 cells which were incubated, with and without either Carbonyl cyanide 3-chlorphenylhydrazon or the apoptosis inducer H(2)O(2). The wo-FLT, which is a non-imaging quantitative measurement, was able to detect several fluorescence decay components and corresponding weights in a single cell resolution. Following cell treatment, both decay time and weight were altered. Results suggest that the prominent factor responsible for these alterations and in some cases to a shift in emission spectrum as well, is the intracellular fluorophore local concentration. In this study it was demonstrated that the proposed wo-FLT method is superior to color fluorescence based imaging in cases where the emission spectrum of a fluorophore remains unchanged during the investigated process. The proposed wo-FLT approach may be of particular importance when direct imaging is impossible.
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Zhao Q, Young IT, de Jong JGS. Photon budget analysis for fluorescence lifetime imaging microscopy. JOURNAL OF BIOMEDICAL OPTICS 2011; 16:086007. [PMID: 21895319 DOI: 10.1117/1.3608997] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We have constructed a mathematical model to analyze the photon efficiency of frequency-domain fluorescence lifetime imaging microscopy (FLIM). The power of the light source needed for illumination in a FLIM system and the signal-to-noise ratio of the detector have led us to a photon "budget." These measures are relevant to many fluorescence microscope users and the results are not restricted to FLIM but applicable to widefield fluorescence microscopy in general. Limitations in photon numbers, however, are more of an issue with FLIM compared to other less quantitative types of imaging. By modeling a typical experimental configuration, examples are given for fluorophores whose absorption peaks span the visible spectrum from Fura-2 to Cy5. We have performed experiments to validate the assumptions and parameters used in our mathematical model. The influence of fluorophore concentration on the intensity of the fluorescence emission light and the Poisson distribution assumption of the detected fluorescence emission light have been validated. The experimental results agree well with the mathematical model. This photon budget is important in order to characterize the constraints involved in current fluorescent microscope systems that are used for lifetime as well as intensity measurements and to design and fabricate new systems.
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Affiliation(s)
- Qiaole Zhao
- Delft University of Technology, Department of Imaging Science and Technology, The Netherlands
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20
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Ganguly S, Clayton AHA, Chattopadhyay A. Fixation alters fluorescence lifetime and anisotropy of cells expressing EYFP-tagged serotonin1A receptor. Biochem Biophys Res Commun 2011; 405:234-7. [PMID: 21219865 DOI: 10.1016/j.bbrc.2011.01.016] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2010] [Accepted: 01/05/2011] [Indexed: 11/15/2022]
Abstract
Fluorescence microscopic approaches represent powerful techniques to monitor molecular interactions in the cellular milieu. Measurements of fluorescence lifetime and anisotropy enjoy considerable popularity in this context. These measurements are often performed on live as well as fixed cells. We report here that formaldehyde-induced cell fixation introduces heterogeneities in the fluorescence emission of serotonin(1A) receptors tagged to enhanced yellow fluorescent protein, and alters fluorescence lifetime and anisotropy significantly. To the best of our knowledge, our results constitute the first report on the effect of formaldehyde fixation on fluorescence parameters of cellular proteins. We conclude that fluorescence parameters derived from fixed cells should be interpreted with caution.
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Affiliation(s)
- Sourav Ganguly
- Centre for Cellular and Molecular Biology, Council of Scientific and Industrial Research, Uppal Road, Hyderabad 500 007, India
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21
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Elder AD, Kaminski CF, Frank JH. phi2FLIM: a technique for alias-free frequency domain fluorescence lifetime imaging. OPTICS EXPRESS 2009; 17:23181-23203. [PMID: 20052246 DOI: 10.1364/oe.17.023181] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
A new approach to alias-free wide-field fluorescence lifetime imaging in the frequency domain is demonstrated using a supercontinuum source for fluorescence excitation and a phase-modulated image intensifier for detection. This technique is referred to as phi-squared fluorescence lifetime imaging (phi(2)FLIM). The phase modulation and square-wave gating of the image intensifier eliminate aliasing by the effective suppression of higher harmonics. The ability to use picosecond excitation pulses without aliasing expands the range of excitation sources available for frequency-domain fluorescence lifetime imaging (fd-FLIM) and improves the modulation depth of conventional homodyne fd-FLIM measurements, which use sinusoidal intensity modulation of the excitation source. The phi(2)FLIM results are analyzed using AB-plots, which facilitate the identification of mono-exponential and multi-exponential fluorescence decays and provide measurements of the fluorophore fractions in two component mixtures. The rapid acquisition speed of the technique enables lifetime measurements in dynamic systems, such as temporally evolving samples and samples that are sensitive to photo-bleaching. Rapid phi(2)FLIM measurements are demonstrated by imaging the dynamic mixing of two different dye solutions at 5.5 Hz. The tunability of supercontinuum radiation enables excitation wavelength resolved FLIM measurements, which facilitates analysis of samples containing multiple fluorophores with different absorption spectra.
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Affiliation(s)
- Alan D Elder
- Department of Chemical Engineering, University of Cambridge, Cambridge, CB2 3RA, UK
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22
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Janes PW, Wimmer-Kleikamp SH, Frangakis AS, Treble K, Griesshaber B, Sabet O, Grabenbauer M, Ting AY, Saftig P, Bastiaens PI, Lackmann M. Cytoplasmic relaxation of active Eph controls ephrin shedding by ADAM10. PLoS Biol 2009; 7:e1000215. [PMID: 19823572 PMCID: PMC2753297 DOI: 10.1371/journal.pbio.1000215] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2009] [Accepted: 09/01/2009] [Indexed: 11/18/2022] Open
Abstract
Novel imaging strategies reveal a conformational shift in a receptor tyrosine kinase domain that controls ligand shedding by an ADAM metalloprotease. Release of cell surface-bound ligands by A-Disintegrin-And-Metalloprotease (ADAM) transmembrane metalloproteases is essential for signalling by cytokine, cell adhesion, and tyrosine kinase receptors. For Eph receptor ligands, it provides the switch between cell-cell adhesion and repulsion. Ligand shedding is tightly controlled by intrinsic tyrosine kinase activity, which for Eph receptors relies on the release of an inhibitory interaction of the cytoplasmic juxtamembrane segment with the kinase domain. However, a mechanism linking kinase and sheddase activities had remained elusive. We demonstrate that it is a membrane-proximal localisation of the latent kinase domain that prevents ephrin ligand shedding in trans. Fluorescence lifetime imaging microscopy and electron tomography reveal that activation extends the Eph receptor tyrosine kinase intracellular domain away from the cell membrane into a conformation that facilitates productive association with ADAM10. Accordingly, EphA3 mutants with constitutively-released kinase domains efficiently support shedding, even when their kinase is disabled. Our data suggest that this phosphorylation-activated conformational switch of EphA3 directly controls ADAM-mediated shedding. The Eph transmembrane receptors are part of the receptor tyrosine kinase family and play important roles in communication between neighbouring cells. An Eph receptor binds to its ligand, membrane-tethered ephrin, on a neighbouring cell so as to form a stable complex and activate downstream signalling events. One such event is regulation of ADAM10, a transmembrane protease of the ADAM metalloprotease family, which provides a feedback mechanism to Eph signalling. ADAM10 is located on Eph-expressing cells and cleaves ephrin from its membrane tether on the opposite cell (through its so-called sheddase activity), thereby separating the cell-cell connection and allowing the signalling complex to internalise. In other biological contexts, activity of the ADAM metalloprotease family underlies signalling mechanisms such as oncogenic EGF-receptor transactivation, adhesion molecule shedding and cytokine/chemokine release. In general, ADAM function is enhanced when receptor tyrosine signalling is active and repressed when tyrosine kinase signalling is inhibited. However, the mechanism through which receptor tyrosine kinase signalling regulates ADAM10, have remained elusive. By combining fluorescence lifetime imaging microscopy (FLIM) and electron microscopic tomography of EphA3, we have demonstrated in live cells at molecular resolution that tyrosine phosphorylation of activated EphA3 triggers a measurable movement of the kinase domain away from the plasma membrane. Only this conformation of the EphA3 kinase domain away from the plasma membrane permits ADAM10 to come close enough to EphA3 so that it can reach its tightly EphA3-bound substrate, ephrin-A5. Our findings delineate a new regulatory concept in cell-cell communication, whereby control over proteolytic sheddase activity is provided by an activation-induced switch in the conformation of the cytoplasmic domain of a receptor tyrosine kinase, rather than by a cytosolic signalling pathway.
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Affiliation(s)
- Peter W. Janes
- Department of Biochemistry and Molecular Biology, Monash University, Victoria, Australia
| | - Sabine H. Wimmer-Kleikamp
- Department of Biochemistry and Molecular Biology, Monash University, Victoria, Australia
- European Molecular Biology Laboratory, Heidelberg, Germany
- Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | | | - Kane Treble
- Department of Biochemistry and Molecular Biology, Monash University, Victoria, Australia
| | - Bettina Griesshaber
- Department of Biochemistry and Molecular Biology, Monash University, Victoria, Australia
| | - Ola Sabet
- Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | - Markus Grabenbauer
- Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | - Alice Y. Ting
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States of America
| | - Paul Saftig
- Biochemical Institute, Christian-Albrecht-University, Kiel, Germany
| | - Philippe I. Bastiaens
- European Molecular Biology Laboratory, Heidelberg, Germany
- Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
- * E-mail: (PIB); (ML)
| | - Martin Lackmann
- Department of Biochemistry and Molecular Biology, Monash University, Victoria, Australia
- * E-mail: (PIB); (ML)
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Kee HL, Diers JR, Ptaszek M, Muthiah C, Fan D, Lindsey JS, Bocian DF, Holten D. Chlorin-bacteriochlorin energy-transfer dyads as prototypes for near-infrared molecular imaging probes: controlling charge-transfer and fluorescence properties in polar media. Photochem Photobiol 2009; 85:909-20. [PMID: 19222800 DOI: 10.1111/j.1751-1097.2008.00532.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The photophysical properties of two energy-transfer dyads that are potential candidates for near-infrared (NIR) imaging probes are investigated as a function of solvent polarity. The dyads (FbC-FbB and ZnC-FbB) contain either a free base (Fb) or zinc (Zn) chlorin (C) as the energy donor and a free base bacteriochlorin (B) as the energy acceptor. The dyads were studied in toluene, chlorobenzene, 1,2-dichlorobenzene, acetone, acetonitrile and dimethylsulfoxide (DMSO). In both dyads, energy transfer from the chlorin to bacteriochlorin occurs with a rate constant of approximately (5-10 ps)(-1) and a yield of >99% in nonpolar and polar media. In toluene, the fluorescence yields (Phif=0.19) and singlet excited-state lifetimes (tau approximately 5.5 ns) are comparable to those of the benchmark bacteriochlorin. The fluorescence yield and excited-state lifetime decrease as the solvent polarity increases, with quenching by intramolecular electron (or hole) transfer being greater for FbC-FbB than for ZnC-FbB in a given solvent. For example, the Phif and tau values for FbC-FbB in acetone are 0.055 and 1.5 ns and in DMSO are 0.019 and 0.28 ns, whereas those for ZnC-FbB in acetone are 0.12 and 4.5 ns and in DMSO are 0.072 and 2.4 ns. The difference in fluorescence properties of the two dyads in a given polar solvent is due to the relative energies of the lowest energy charge-transfer states, as assessed by ground-state redox potentials and supported by molecular-orbital energies derived from density functional theory calculations. Controlling the extent of excited-state quenching in polar media will allow the favorable photophysical properties of the chlorin-bacteriochlorin dyads to be exploited in vivo. These properties include very large Stokes shifts (85 nm for FbC-FbB, 110 nm for ZnC-FbB) between the red-region absorption of the chlorin and the NIR fluorescence of the bacteriochlorin (lambdaf=760 nm), long bacteriochlorin excited-state lifetime (approximately 5.5 ns), and narrow (<or=20 nm) absorption and fluorescence bands. The latter will facilitate selective excitation/detection and multiprobe applications using both intensity- and lifetime-imaging techniques.
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Affiliation(s)
- Hooi Ling Kee
- Department of Chemistry, Washington University, St. Louis, MO, USA
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24
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Hanley QS. Spectrally resolved fluorescent lifetime imaging. J R Soc Interface 2009; 6. [PMCID: PMC2706466 DOI: 10.1098/rsif.2008.0393.focus] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2008] [Accepted: 11/13/2008] [Indexed: 01/03/2024] Open
Abstract
Placing an imaging spectrograph or related components capable of generating a spectrum between a microscope and the image intensifier of a conventional fluorescence lifetime imaging (FLIM) system creates a spectrally resolved FLIM (SFLIM). This arrangement provides a number of opportunities not readily available to conventional systems using bandpass filters. The examples include: simultaneous viewing of multiple fluorophores; tracking of both the donor and acceptor; and observation of a range of spectroscopic changes invisible to the conventional FLIM systems. In the frequency-domain implementation of the method, variation in the fractional contributions from different fluorophores along the wavelength dimension can behave as a surrogate for a frequency sweep or spatial variations while analysing fluorophore mixtures. This paper reviews the development of the SFLIM method, provides a theoretical and practical overview of frequency-domain SFLIM including: presentation of the data; manifestations of energy transfer; observation of multiple fluorophores; and the limits of single frequency methods.
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Affiliation(s)
- Quentin S Hanley
- School of Science and Technology, Nottingham Trent UniversityClifton Lane, Nottingham NG11 8NS, UK
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25
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Schlachter S, Elder AD, Esposito A, Kaminski GS, Frank JH, van Geest LK, Kaminski CF. mhFLIM: resolution of heterogeneous fluorescence decays in widefield lifetime microscopy. OPTICS EXPRESS 2009; 17:1557-70. [PMID: 19188985 DOI: 10.1364/oe.17.001557] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Frequency-domain fluorescence lifetime imaging microscopy (FD-FLIM) is a fast and accurate way of measuring fluorescence lifetimes in widefield microscopy. However, the resolution of multiple exponential fluorescence decays has remained beyond the reach of most practical FD-FLIM systems. In this paper we describe the implementation of FD-FLIM using a 40 MHz pulse train derived from a supercontinuum source for excitation. The technique, which we term multi-harmonic FLIM (mhFLIM), makes it possible to accurately resolve biexponential decays of fluorophores without any a priori information. The system's performance is demonstrated using a mixture of spectrally similar dyes of known composition and also on a multiply-labeled biological sample. The results are compared to those obtained from time correlated single photon counting (TCSPC) microscopy and a good level of agreement is achieved. We also demonstrate the first practical application of an algorithm derived by G. Weber [1] for analysing mhFLIM data. Because it does not require nonlinear minimisation, it offers potential for realtime analysis during acquisition.
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Affiliation(s)
- S Schlachter
- Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, UK.
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26
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Verveer PJ, Hanley QS. Chapter 2 Frequency domain FLIM theory, instrumentation, and data analysis. FRET AND FLIM TECHNIQUES 2009. [DOI: 10.1016/s0075-7535(08)00002-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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Esposito A, Schlachter S, Schierle GSK, Elder AD, Diaspro A, Wouters FS, Kaminski CF, Iliev AI. Quantitative fluorescence microscopy techniques. Methods Mol Biol 2009; 586:117-42. [PMID: 19768427 DOI: 10.1007/978-1-60761-376-3_6] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Fluorescence microscopy is a non-invasive technique that allows high resolution imaging of cytoskeletal structures. Advances in the field of fluorescent labelling (e.g., fluorescent proteins, quantum dots, tetracystein domains) and optics (e.g., super-resolution techniques and quantitative methods) not only provide better images of the cytoskeleton, but also offer an opportunity to quantify the complex of molecular events that populate this highly organised, yet dynamic, structure.For instance, fluorescence lifetime imaging microscopy and Förster resonance energy transfer imaging allow mapping of protein-protein interactions; furthermore, techniques based on the measurement of photobleaching kinetics (e.g., fluorescence recovery after photobleaching, fluorescence loss in photobleaching, and fluorescence localisation after photobleaching) permit the characterisation of axonal transport and, more generally, diffusion of relevant biomolecules.Quantitative fluorescence microscopy techniques offer powerful tools for understanding the physiological and pathological roles of molecular machineries in the living cell.
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Affiliation(s)
- Alessandro Esposito
- Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, UK
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Selective detection of NADPH oxidase in polymorphonuclear cells by means of NAD(P)H-based fluorescence lifetime imaging. JOURNAL OF BIOPHYSICS 2008; 2008:602639. [PMID: 20107577 PMCID: PMC2809359 DOI: 10.1155/2008/602639] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/28/2008] [Accepted: 09/02/2008] [Indexed: 11/18/2022]
Abstract
NADPH oxidase (NOX2) is a multisubunit membrane-bound enzyme complex that, upon assembly in activated cells,
catalyses the reduction of free oxygen to its superoxide anion, which further leads to reactive oxygen species (ROS) that are
toxic to invading pathogens, for example, the fungus Aspergillus fumigatus. Polymorphonuclear cells (PMNs) employ both
nonoxidative and oxidative mechanisms to clear this fungus from the lung. The oxidative mechanisms mainly depend on the
proper assembly and function of NOX2. We identified for the first time the NAD(P)H-dependent enzymes involved in such
oxidative mechanisms by means of biexponential NAD(P)H-fluorescence lifetime imaging (FLIM). A specific fluorescence
lifetime of 3670±140 picoseconds as compared to 1870 picoseconds for NAD(P)H bound to mitochondrial enzymes could be
associated with NADPH bound to oxidative enzymes in activated PMNs. Due to its predominance in PMNs and due to the
use of selective activators and inhibitors, we strongly believe that this specific lifetime mainly originates from NOX2. Our
experiments also revealed the high site specificity of the NOX2 assembly and, thus, of the ROS production as well as the
dynamic nature of these phenomena. On the example of NADPH oxidase, we demonstrate the potential of NAD(P)H-based
FLIM in selectively investigating enzymes during their cellular function.
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29
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Kee HL, Nothdurft R, Muthiah C, Diers JR, Fan D, Ptaszek M, Bocian DF, Lindsey JS, Culver JP, Holten D. Examination of Chlorin-Bacteriochlorin Energy-transfer Dyads as Prototypes for Near-infrared Molecular Imaging Probes†. Photochem Photobiol 2008; 84:1061-72. [DOI: 10.1111/j.1751-1097.2008.00409.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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30
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Hille C, Berg M, Bressel L, Munzke D, Primus P, Löhmannsröben HG, Dosche C. Time-domain fluorescence lifetime imaging for intracellular pH sensing in living tissues. Anal Bioanal Chem 2008; 391:1871-9. [DOI: 10.1007/s00216-008-2147-0] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2008] [Accepted: 04/16/2008] [Indexed: 10/22/2022]
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31
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Niesner RA, Andresen V, Gunzer M. Intravital two-photon microscopy: focus on speed and time resolved imaging modalities. Immunol Rev 2008; 221:7-25. [PMID: 18275472 DOI: 10.1111/j.1600-065x.2008.00582.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Initially used mainly in the neurosciences, two-photon microscopy has become a powerful tool for the analysis of immunological processes. Here, we describe currently available two-photon microscopy techniques with a focus on novel approaches that allow very high image acquisition rates compared with state-of-the-art systems. This improvement is achieved through a parallelization of the excitation process: multiple beams scan the sample simultaneously, and the fluorescence is collected with sensitive charge-coupled device (CCD)-based line or field detectors. The new technique's performance is compared with conventional single beam laser-scanning systems that detect signals by means of photomultipliers. We also discuss the use of time- and polarization-resolved fluorescence detection, especially fluorescence lifetime imaging (FLIM), which goes beyond simple detection of cells and tissue structures and allows insight into cellular physiology. We focus on the analysis of endogenous fluorophores such as NAD(P)H as a way to analyze the redox status in cells with subcellular resolution. Here, high-speed imaging setups in combination with novel ways of data analysis allow the generation of FLIM data sets almost in real time. The implications of this technology for the analysis of immune reactions and other cellular processes are discussed.
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Affiliation(s)
- Raluca A Niesner
- Junior Research Group Immunodynamics, Helmholtz Centre for Infection Research, Braunschweig, Germany
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32
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Quantitative lifetime unmixing of multiexponentially decaying fluorophores using single-frequency fluorescence lifetime imaging microscopy. Biophys J 2008; 95:378-89. [PMID: 18359789 DOI: 10.1529/biophysj.107.125229] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Fluorescence lifetime imaging microscopy (FLIM) is a quantitative microscopy technique for imaging nanosecond decay times of fluorophores. In the case of frequency-domain FLIM, several methods have been described to resolve the relative abundance of two fluorescent species with different fluorescence decay times. Thus far, single-frequency FLIM methods generally have been limited to quantifying two species with monoexponential decay. However, multiexponential decays are the norm rather than the exception, especially for fluorescent proteins and biological samples. Here, we describe a novel method for determining the fractional contribution in each pixel of an image of a sample containing two (multiexponentially) decaying species using single-frequency FLIM. We demonstrate that this technique allows the unmixing of binary mixtures of two spectrally identical cyan or green fluorescent proteins, each with multiexponential decay. Furthermore, because of their spectral identity, quantitative images of the relative molecular abundance of these fluorescent proteins can be generated that are independent of the microscope light path. The method is rigorously tested using samples of known composition and applied to live cell microscopy using cells expressing multiple (multiexponentially decaying) fluorescent proteins.
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Müller-Taubenberger A, Anderson KI. Recent advances using green and red fluorescent protein variants. Appl Microbiol Biotechnol 2007; 77:1-12. [PMID: 17704916 DOI: 10.1007/s00253-007-1131-5] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2007] [Revised: 07/12/2007] [Accepted: 07/14/2007] [Indexed: 11/28/2022]
Abstract
Fluorescent proteins have proven to be excellent tools for live-cell imaging. In addition to green fluorescent protein (GFP) and its variants, recent progress has led to the development of monomeric red fluorescent proteins (mRFPs) that show improved properties with respect to maturation, brightness, and the monomeric state. This review considers green and red spectral variants, their paired use for live-cell imaging in vivo, in vitro, and in fluorescence resonance energy transfer (FRET) studies, in addition to other recent "two-color" advances including photoswitching and bimolecular fluorescence complementation (BiFC). It will be seen that green and red fluorescent proteins now exist with nearly ideal properties for dual-color microscopy and FRET.
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Affiliation(s)
- Annette Müller-Taubenberger
- Institut für Zellbiologie (ABI), Ludwig-Maximilians-Universität München, Schillerstrasse 42, Munich, Germany.
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35
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Smith TA, Bird DK, Nuske JW. Phase-locked 10 MHz reference signal for frequency domain time-resolved fluorescence measurements. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2007; 78:053715. [PMID: 17552833 DOI: 10.1063/1.2740475] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
A complete electronic system that is suitable for use in megahertz frequency domain time-resolved fluorescence instruments based on mode-locked lasers is described. The circuit produces a 10 MHz signal, phase locked to the mode-locked laser pulse frequency, which is required by many commercial frequency synthesizers as the external reference signal. This device is particularly useful in conjunction with ultrafast gated intensified charge coupled device cameras capable of being frequency modulated for time-resolved fluorescence imaging.
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Affiliation(s)
- Trevor A Smith
- Ultrafast and Microspectroscopy Laboratories, School of Chemistry, The University of Melbourne, Victoria 3010, Australia.
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36
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Spriet C, Trinel D, Waharte F, Deslee D, Vandenbunder B, Barbillat J, Héliot L. Correlated fluorescence lifetime and spectral measurements in living cells. Microsc Res Tech 2007; 70:85-94. [PMID: 17152071 DOI: 10.1002/jemt.20385] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Studies of proteins' interaction in cells by FRET can take benefit from two important photo-physical properties describing fluorescent proteins: fluorescence emission spectrum and fluorescence lifetime. These properties provide specific and complementary information about the tagged proteins and their environment. However, none of them taken individually can completely quantify the involved fluorophore characteristics due to their multiparametric dependency with molecular environment, experimental conditions, and interpretation complexity. A solution to get a better understanding of the biological process implied at the cellular level is to combine the spectral and temporal fluorescence data acquired simultaneously at every cell region under investigation. We present the SLiM-SPRC160, an original temporal/spectral acquisition system for simultaneous lifetime measurements in 16 spectral channels directly attached to the descanned port of a confocal microscope with two-photon excitation. It features improved light throughput, enabling low-level excitation and minimum invasivity in living cells studies. To guarantee a fairly good level of accuracy and reproducibility in the measurements of fluorescence lifetime and spectra on living cells, we propose a rigorous protocol for running experiments with this new equipment that preserves cell viability. The usefulness of SLiM approach for the precise determination of overlapping fluorophores is illustrated with the study of known solutions of rhodamine. Then, we describe reliable FRET experiments in imaging mode realized in living cells using this protocol. We also demonstrate the benefit of localized fluorescence spectrum-lifetime acquisitions for the dynamic study of fluorescent proteins. proteins.
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Affiliation(s)
- Corentin Spriet
- Biophotonique Cellulaire Fonctionnelle, FRE 2963, Institut de Recherche Interdisciplinaire, 59021 Lille Cedex, France
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37
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Festy F, Ameer-Beg SM, Ng T, Suhling K. Imaging proteins in vivo using fluorescence lifetime microscopy. MOLECULAR BIOSYSTEMS 2007; 3:381-91. [PMID: 17533451 DOI: 10.1039/b617204k] [Citation(s) in RCA: 103] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Fluorescence lifetime imaging (FLIM) represents a key optical technique for imaging proteins and protein interaction in vivo. We review the principles and recent advances in the application of the technique, instrumentation and molecular probe development.
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Affiliation(s)
- Frederic Festy
- Randall Division of Cell and Molecular Biophysics, King's College London, London, UK SE1 1UL
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Elder AD, Frank JH, Swartling J, Dai X, Kaminski CF. Calibration of a wide-field frequency-domain fluorescence lifetime microscopy system using light emitting diodes as light sources. J Microsc 2006; 224:166-80. [PMID: 17204064 DOI: 10.1111/j.1365-2818.2006.01689.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
High brightness light emitting diodes are an inexpensive and versatile light source for wide-field frequency-domain fluorescence lifetime imaging microscopy. In this paper a full calibration of an LED based fluorescence lifetime imaging microscopy system is presented for the first time. A radio-frequency generator was used for simultaneous modulation of light emitting diode (LED) intensity and the gain of an intensified charge coupled device (CCD) camera. A homodyne detection scheme was employed to measure the demodulation and phase shift of the emitted fluorescence, from which phase and modulation lifetimes were determined at each image pixel. The system was characterized both in terms of its sensitivity to measure short lifetimes (500 ps to 4 ns), and its capability to distinguish image features with small lifetime differences. Calibration measurements were performed in quenched solutions containing Rhodamine 6G dye and the results compared to several independent measurements performed with other measurement methodologies, including time correlated single photon counting, time gated detection, and acousto optical modulator (AOM) based modulation of excitation sources. Results are presented from measurements and simulations. The effects of limited signal-to-noise ratios, baseline drifts and calibration errors are discussed in detail. The implications of limited modulation bandwidth of high brightness, large area LED devices ( approximately 40 MHz for devices used here) are presented. The results show that phase lifetime measurements are robust down to sub ns levels, whereas modulation lifetimes are prone to errors even at large signal-to-noise ratios. Strategies for optimizing measurement fidelity are discussed. Application of the fluorescence lifetime imaging microscopy system is illustrated with examples from studies of molecular mixing in microfluidic devices and targeted drug delivery research.
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Affiliation(s)
- A D Elder
- Department of Chemical Engineering, University of Cambridge, Pembroke Street, Cambridge, UK
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Yasuda R. Imaging spatiotemporal dynamics of neuronal signaling using fluorescence resonance energy transfer and fluorescence lifetime imaging microscopy. Curr Opin Neurobiol 2006; 16:551-61. [PMID: 16971112 DOI: 10.1016/j.conb.2006.08.012] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2006] [Accepted: 08/30/2006] [Indexed: 11/26/2022]
Abstract
The spatiotemporal localization of neuronal signaling is important for triggering neuronal responses in specific locations at precise times. Fluorescence resonance energy transfer imaging enables measurement of spatiotemporal dynamics of signaling activity in live neurons. Although the usefulness of fluorescence resonance energy transfer is well recognized, there are many difficulties in applying it, particularly when imaging in neuronal micro-compartments in light-scattering brain tissue. Fluorescence resonance energy transfer has been imaged using several techniques including intensity-based methods, fluorescence lifetime imaging and fluorescence anisotropy imaging. These methods have different advantages and disadvantages, and thus are suitable in different applications.
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Affiliation(s)
- Ryohei Yasuda
- Neurobiology Department, Duke University Medical Center, Research Drive, Durham, NC 27710 USA.
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Abstract
We present a method to document ciliary beat frequency with the linescan function of a scanning confocal microscope, using ciliated tracheal cells and free-swimming rotifers as examples. Depending on the clarity of the original data, the ciliary beat frequency can be determined from the confocal linescan directly or from an intensity linescan analysis of the original data. Fast Fourier transform treatment of the data can be used to verify the derived ciliary beat frequency. The linescan approach allows analysis of simple ciliary movements displayed by the ciliated tracheal cells, as well as complex movements performed by free-swimming rotifers while feeding.
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Affiliation(s)
- R T Doyle
- Department of Genetics, Development and Cell Biology, Roy J. Carver Laboratory of Ultrahigh Resolution Biological Microscopy, Institute for Combinatorial Discovery, Iowa State University, Ames, IA 50011, USA.
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Kremers GJ, Goedhart J, van Munster EB, Gadella TWJ. Cyan and yellow super fluorescent proteins with improved brightness, protein folding, and FRET Förster radius. Biochemistry 2006; 45:6570-80. [PMID: 16716067 DOI: 10.1021/bi0516273] [Citation(s) in RCA: 342] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Enhanced cyan and yellow fluorescent proteins are widely used for dual color imaging and protein-protein interaction studies based on fluorescence resonance energy transfer. Use of these fluorescent proteins can be limited by their thermosensitivity, dim fluorescence, and tendency for aggregation. Here we report the results of a site-directed mutagenesis approach to improve these fluorescent proteins. We created monomeric optimized variants of ECFP and EYFP, which fold faster and more efficiently at 37 degrees C and have superior solubility and brightness. Bacteria expressing SCFP3A were 9-fold brighter than those expressing ECFP and 1.2-fold brighter than bacteria expressing Cerulean. SCFP3A has an increased quantum yield (0.56) and fluorescence lifetime. Bacteria expressing SYFP2 were 12 times brighter than those expressing EYFP(Q69K) and almost 2-fold brighter than bacteria expressing Venus. In HeLa cells, the improvements were less pronounced; nonetheless, cells expressing SCFP3A and SYFP2 were both 1.5-fold brighter than cells expressing ECFP and EYFP(Q69K), respectively. The enhancements of SCFP3A and SYFP2 are most probably due to an increased intrinsic brightness (1.7-fold and 1.3-fold for purified recombinant proteins, compared to ECFP & EYFP(Q69K), respectively) and due to enhanced protein folding and maturation. The latter enhancements most significantly contribute to the increased fluorescent yield in bacteria whereas they appear less significant for mammalian cell systems. SCFP3A and SYFP2 make a superior donor-acceptor pair for fluorescence resonance energy transfer, because of the high quantum yield and increased lifetime of SCFP3A and the high extinction coefficient of SYFP2. Furthermore, SCFP1, a CFP variant with a short fluorescence lifetime but identical spectra compared to ECFP and SCFP3A, was characterized. Using the large lifetime difference between SCFP1 and SCFP3A enabled us to perform for the first time dual-lifetime imaging of spectrally identical fluorescent species in living cells.
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Affiliation(s)
- Gert-Jan Kremers
- Section Molecular Cytology and Centre for Advanced Microscopy, Swammerdam Institute for Life Sciences, University of Amsterdam, Kruislaan 316, 1098 SM, Amsterdam, The Netherlands
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Abstract
The brain is complex and dynamic. The spatial scales of interest to the neurobiologist range from individual synapses (approximately 1 microm) to neural circuits (centimeters); the timescales range from the flickering of channels (less than a millisecond) to long-term memory (years). Remarkably, fluorescence microscopy has the potential to revolutionize research on all of these spatial and temporal scales. Two-photon excitation (2PE) laser scanning microscopy allows high-resolution and high-sensitivity fluorescence microscopy in intact neural tissue, which is hostile to traditional forms of microscopy. Over the last 10 years, applications of 2PE, including microscopy and photostimulation, have contributed to our understanding of a broad array of neurobiological phenomena, including the dynamics of single channels in individual synapses and the functional organization of cortical maps. Here we review the principles of 2PE microscopy, highlight recent applications, discuss its limitations, and point to areas for future research and development.
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Affiliation(s)
- Karel Svoboda
- HHMI, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA.
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Elson DS, Galletly N, Talbot C, Requejo-Isidro J, McGinty J, Dunsby C, Lanigan PMP, Munro I, Benninger RKP, de Beule P, Auksorius E, Hegyi L, Sandison A, Wallace A, Soutter P, Neil MAA, Lever J, Stamp GW, French PMW. Multidimensional Fluorescence Imaging Applied to Biological Tissue. REVIEWS IN FLUORESCENCE 2006 2006. [DOI: 10.1007/0-387-33016-x_22] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
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Becker W, Bergmann A, Haustein E, Petrasek Z, Schwille P, Biskup C, Kelbauskas L, Benndorf K, Klöcker N, Anhut T, Riemann I, König K. Fluorescence lifetime images and correlation spectra obtained by multidimensional time-correlated single photon counting. Microsc Res Tech 2006; 69:186-95. [PMID: 16538624 DOI: 10.1002/jemt.20251] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Multidimensional time-correlated single photon counting (TCSPC) is based on the excitation of the sample by a high-repetition rate laser and the detection of single photons of the fluorescence signal in several detection channels. Each photon is characterized by its arrival time in the laser period, its detection channel number, and several additional variables such as the coordinates of an image area, or the time from the start of the experiment. Combined with a confocal or two-photon laser scanning microscope and a pulsed laser, multidimensional TCSPC makes a fluorescence lifetime technique with multiwavelength capability, near-ideal counting efficiency, and the capability to resolve multiexponential decay functions. We show that the same technique and the same hardware can be used for precision fluorescence decay analysis and fluorescence correlation spectroscopy (FCS) in selected spots of a sample.
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Affiliation(s)
- W Becker
- Becker & Hickl GmbH, 12277 Berlin, Germany.
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Redford GI, Clegg RM. Polar Plot Representation for Frequency-Domain Analysis of Fluorescence Lifetimes. J Fluoresc 2005; 15:805-15. [PMID: 16341800 DOI: 10.1007/s10895-005-2990-8] [Citation(s) in RCA: 204] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2005] [Accepted: 07/19/2005] [Indexed: 10/25/2022]
Abstract
We present applications of polar plots for analyzing fluorescence lifetime data acquired in the frequency domain. This graphical, analytical method is especially useful for rapid FLIM measurements. The usual method for sorting out and determining the underlying lifetime components from a complex fluorescence signal is to carry out the measurement at multiple frequencies. When it is not possible to measure at more than one frequency, such as rapid lifetime imaging, specific features of the polar plot analysis yield valuable information, and provide a diagnostic visualization of the participating fluorescent species underlying a complex lifetime distributions. Data are presented where this polar plot presentation is useful to derive valuable, unique information about the underlying component distributions. We also discuss artifacts of photolysis and how this method can also be applied to samples where each fluorescence species shows a continuous distribution of lifetimes. Polar plots of frequency-domain data are commonly used for analysis of dielectric relaxation experiments (Cole-Cole plots), which have proved to be exceptionally useful in that field for decades. We compare this analytical tool that is well developed and extensively used in dielectric relaxation and chemical kinetics to fluorescence measurements.
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Affiliation(s)
- Glen I Redford
- Physics Department, University of Illinois, Urbana-Champaign, Illinois, USA
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Peyker A, Rocks O, Bastiaens PIH. Imaging activation of two Ras isoforms simultaneously in a single cell. Chembiochem 2005; 6:78-85. [PMID: 15637661 DOI: 10.1002/cbic.200400280] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Fluorescence resonance energy transfer (FRET) microscopy approaches have been used to study protein interactions in living cells. Up to now, due to the spectral requirements for FRET detection, this has been limited to the measurement of single protein interactions. Here we present a novel time-resolved fluorescence imaging method for simultaneously monitoring the activation state of two proteins in a single cell. A Ras sensor, consisting of fluorescently labelled Ras and a fluorescently labelled Ras binding domain (RBD) of Raf, which reads out Ras activation by its interaction with RBD as a FRET signal, has been adapted for this purpose. By using yellow (YFP) and cyan (CFP) versions of the green fluorescent protein from Aquorea victoria as donors and a tandem construct of Heteractis crispa Red (tHcRed) as acceptor for both donors, two independent FRET signals can be measured at the same time. Measuring the YFP and CFP donor lifetimes by fluorescence-lifetime imaging microscopy (FLIM) allows us to distinguish the two different FRET signals in a single cell. Using this approach, we show that different Ras isoforms and mutants that localize to the plasma membrane, to the Golgi or to both compartments display distinct activation profiles upon growth-factor stimulation; this indicates that there is a differential regulation in cellular compartments. The method presented here is especially useful when studying spatiotemporal aspects of protein regulation as part of larger cellular signalling networks.
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Affiliation(s)
- Anna Peyker
- European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany
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Niesner R, Peker B, Schlüsche P, Gericke KH, Hoffmann C, Hahne D, Müller-Goymann C. 3D-resolved investigation of the pH gradient in artificial skin constructs by means of fluorescence lifetime imaging. Pharm Res 2005; 22:1079-87. [PMID: 16028008 DOI: 10.1007/s11095-005-5304-6] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2005] [Accepted: 04/14/2005] [Indexed: 10/25/2022]
Abstract
PURPOSE The development of substitutes for the human skin, e.g., artificial skin constructs (ASCs), is of particular importance for pharmaceutical and dermatologic research because they represent economical test samples for the validation of new drugs. In this regard, it is essential for the skin substitutes to be reliable models of the genuine skin, i.e., to have similar morphology and functionality. Particularly important is the barrier function, i.e., the selective permeability of the skin, which is strongly related to the epidermal pH gradient. Because the pH significantly influences the permeation profile of ionizable drugs such as nonsteroidal anti-inflammatory drugs, it is of major importance to quantitatively measure the epidermal pH gradient of the ASC and compare it to that of genuine skin. METHODS Using three-dimensional fluorescence lifetime imaging combined with two-photon scanning microscopy, we measured with submicron resolution the three-dimensional pH gradient in the epidermis of ASCs stained with 2',7'-bis-(2-carboxyethyl)-5/6-carboxyfluorescein. RESULTS Similar to genuine skin, the surface of the artificial epidermis has an acidic character (pH 5.9), whereas in the deeper layers the pH increases up to 7.0. Moreover, the pH gradient differs in the cell interior (maximally 7.2) and in the intercellular matrix (maximally 6.6). Apart from the similitude of the pH distribution, the genuine and the artificial skin prove to have similar morphologies and to be characterized by similar distributions of the refractive index. CONCLUSIONS Artificial skin is a reliable model of genuine human skin, e.g., in permeability studies, because it is characterized by a similar pH gradient, a similar morphology, and a similar distribution of the refractive index to that of genuine skin.
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Affiliation(s)
- Raluca Niesner
- Institute for Physical and Theoretical Chemistry, Technical University, Braunschweig, Germany.
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CHEN YE, PERIASAMY AMMMASI. Time-Correlated Single-Photon Counting Fluorescence Lifetime Imaging–FRET Microscopy for Protein Localization. Mol Imaging 2005. [DOI: 10.1016/b978-019517720-6.50022-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
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van Munster EB, Gadella TWJ. Suppression of photobleaching-induced artifacts in frequency-domain FLIM by permutation of the recording order. Cytometry A 2004; 58:185-94. [PMID: 15057972 DOI: 10.1002/cyto.a.20013] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
BACKGROUND Photobleaching can lead to significant errors in frequency-domain fluorescence lifetime imaging microscopy (FLIM). Existing correction methods for photobleaching require additional recordings and processing time and can result in additional noise. A method is introduced that suppresses the effects of photobleaching without the need for extra recordings or processing. METHODS Existing bleach correction methods and the method introduced in this report whereby the recording order of the phases is permuted were compared using numerical simulations. RESULTS Certain orders were found to make measurements virtually insensitive to photobleaching. At 12 recordings, errors in measured phase and modulation depth decreased by a factor 512 and 393, respectively, compared to recordings using sequential recording order. The optimal order is independent of modulation depth, phase, and extent of photobleaching. Thus, the same order can be used for practically all situations. Application of the method in FLIM measurements of EYFP-transfected HeLa cells was found effectively to suppress photobleaching induced artifacts. CONCLUSIONS In view of the ease of implementation, its inherent robustness, and the possibility to still apply existing correction methods afterward, there is no good reason not to use the permuted recording order presented in this report instead of a sequential order.
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Affiliation(s)
- Erik B van Munster
- Molecular Cytology Section, Swammerdam Institute for Life Sciences, University of Amsterdam, Amsterdam, The Netherlands.
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