Fluorescence lifetime of Rhodamine B in aqueous solutions of polysaccharides and proteins as a function of viscosity and temperature

Poly(styrene sulfonate-co-glycidyl methacrylate)/Rhodamine B Films with Enhanced Energy Conversion in Luminescent Solar Concentrators Triggered by Aromatic-Aromatic Interactions

Styrene sulfonate-glycidyl methacrylate copolymers have been rationally designed to furnish both insolubility in water and negatively charged aromatic functional groups that, upon undergoing aromatic-aromatic interactions with dyes, impart specific functionality to solid materials. Solid films incorporating varying amounts of the embedded fluorophore rhodamine B were obtained by solution casting of the copolymers onto glass substrates. The formed slabs were then evaluated for their potential use in energy conversion devices such as luminescent solar concentrators. The materials presented higher dye dispersion, avoiding nonfluorescent aggregates, increased fluorescence emission intensity, larger Stokes shift, lower absorption and emission overlap, reduced reabsorption, and longer fluorescence lifetime, compared with matrices made of rhodamine B/poly(methyl methacrylate). The higher dispersion, polarity, and charge transfer character in the excited state are claimed as the cause of these photophysical properties produced by the functional polymers. Tested in luminescent solar concentrator devices of 50 × 50 × 4 mm3, the device efficiency obtained reached 1.19%, whereas control devices made with rhodamine B/poly(methyl methacrylate) matrices only reached 0.33%. This aims at functional polymers containing aromatic charged residues in the solid state as potential tools to achieve improved performance in energy conversion devices based on the modulation of the photophysical response of aromatic dyes by means of aromatic-aromatic interactions.

Insights into metabolic changes during epidermal differentiation as revealed by multiphoton microscopy with fluorescence lifetime imaging

Rapid developments in the field of organotypic cultures have generated a growing need for effective and non-invasive methods for quality control during tissue development. In this study, we correlate metabolic changes with epidermal differentiation and demonstrate that multiphoton microscopy with fluorescence lifetime imaging (MPM-FLIM) can be applied to monitor epidermal differentiation of keratinocytes with respect to proliferative and differentiated states. In a 2D keratinocyte tissue culture model, increased expression of differentiation markers keratin-1 and keratin-10 was induced with calcium supplementation. An accompanying shift from glycolysis to mitochondrial respiration was detected in metabolic flux assays. Analysis of MPM-FLIM images acquired at 750 nm and 900 nm excitation revealed a decreased relative fraction of intracellular NADH and FAD after high calcium treatment, consistent with increased oxidative phosphorylation. Epidermal differentiation could be monitored over a 96 h period. Discrimination analysis based on k-means clustering generated clusters that correlated well with the duration of high Ca2+ treatment, suggesting that MPM-FLIM can provide useful parameters for monitoring keratinocyte differentiation.

Nanoengineering Spikey Surfaces: Investigation of Reversible Organizational Control of Surface-Tethered Polypeptide Brushes

Nature serves as an important source of inspiration for the innovation and development of micro- and nanostructures for advanced functional surfaces and substrates. One example used in nature is a spikey surface ranging from micrometer-sized spikes on pollen grains down to the nanometer-scale protein spikes found on viruses. This study explored the realization of such highly textured surfaces via the nanoengineering of self-assembled poly(γ-benzyl-l-glutamate) "nanospikes", exploiting solvent-induced chain organization, controlled surface chemical functionality, and enhanced stability in the form of polymer brushes. The reversible solvent-responsive behavior of these polymer chains and the aggregation behavior of the chain-ends were investigated via fluorescence characterization and studied through molecular simulations. Vapor-based solvent treatments were developed for orientation control with in situ analysis to understand film response and brush organizational behavior under different selected conditions. The effect of sub-100 nm nanopatterning on surface morphology and chain organization was examined via an integrated approach of experimental and computational studies. The methodologies established in this study present opportunities for engineering sophisticated nanoscale spikey surfaces with high customizability by means of nanolithography combined with solvent-assisted treatments.

N-octylpyridine hydrogen sulphate ionic liquid for multifunctional fluorescent response in different solvents

Ionic liquids (ILs) have attracted considerable interest in the last two decades owing to their unique fluorescent properties. Herein, N-octylpyridine hydrogen sulphate ([OP]HSO4) was synthesised and characterised using 1H NMR and infrared spectroscopies. In addition, the fluorescence spectra of [OP]HSO4 in water, methanol, ethanol and acetonitrile were studied. In a single solvent, as the concentration of the solvent (methanol, ethanol or acetonitrile) increases, the fluorescence intensity of the IL first increases and then decreases. A similar trend was observed in their mixed solvents with water. Moreover, the fluorescence intensity of [OP]HSO4 decreases with increasing temperature. A fluorescence intensity reduction of only 4.46% for [OP]HSO4 after continuous scanning for 40 cycles under the maximum excitation state was analysed. The lack of photobleaching observed in [OP]HSO4 indicates its good photobleaching resistance.

More than double the fun with two-photon excitation microscopy

For generations researchers have been observing the dynamic processes of life through the lens of a microscope. This has offered tremendous insights into biological phenomena that span multiple orders of time- and length-scales ranging from the pure magic of molecular reorganization at the membrane of immune cells, to cell migration and differentiation during development or wound healing. Standard fluorescence microscopy techniques offer glimpses at such processes in vitro, however, when applied in intact systems, they are challenged by reduced signal strengths and signal-to-noise ratios that result from deeper imaging. As a remedy, two-photon excitation (TPE) microscopy takes a special place, because it allows us to investigate processes in vivo, in their natural environment, even in a living animal. Here, we review the fundamental principles underlying TPE aimed at basic and advanced microscopy users interested in adopting TPE for intravital imaging. We focus on applications in neurobiology, present current trends towards faster, wider and deeper imaging, discuss the combination with photon counting technologies for metabolic imaging and spectroscopy, as well as highlight outstanding issues and drawbacks in development and application of these methodologies.

A Toxicogenic Interaction between Intracellular Amyloid-β and Apolipoprotein-E

Alzheimer's disease (AD) is associated with the aggregation of amyloid β (Aβ) and tau proteins. Why ApoE variants are significant genetic risk factors remains a major unsolved puzzle in understanding AD, although intracellular interactions with ApoE are suspected to play a role. Here, we show that specific changes in the fluorescence lifetime of fluorescently tagged small Aβ oligomers in rat brain cells correlate with the cellular ApoE content. An inhibitor of the Aβ-ApoE interaction suppresses these changes and concomitantly reduces Aβ toxicity in a dose-dependent manner. Single-molecule techniques show changes both in the conformation and in the stoichiometry of the oligomers. Neural stem cells derived from hiPSCs of Alzheimer's patients also exhibit these fluorescence lifetime changes. We infer that intracellular interaction with ApoE modifies the N-terminus of the Aβ oligomers, inducing changes in their stoichiometry, membrane affinity, and toxicity. These changes can be directly imaged in live cells and can potentially be used as a rapid and quantitative cellular assay for AD drug discovery.

A plasmonic fluorescent ratiometric temperature sensor for self-limiting hyperthermic applications utilizing FRET enhancement in the plasmonic field

Nanoparticle mediated photo-induced hyperthermia holds much promise as a therapeutic solution for the management of diseases like cancer. The conventional methods of temperature measurements do not measure the actual temperature generated in the vicinity of the nanoparticles during illumination. In contrast, nano temperature sensors built on hyperthermic nanoparticles can relay local temperatures around the nanoparticles during thermal induction. In this study, we present a core shell construct consisting of a plasmonic core and a silica shell encapsulating a FRET pair of organic dyes for such application. The plasmonic core imparts photo-induced hyperthermic properties to the nanoconstruct, while the fluorescent shell enables ratiometric sensing of temperature. We see that even at a low dye encapsulation concentration, the shell displays a linear ratiometric fluorescence response to temperature and high energy transfer between the dye pair. Interestingly, Monte Carlo simulations, without considering the plasmonic core, show that the energy transfer in the system should be much smaller than that observed, confirming plasmon enhancement in the FRET energy transfer. We also show the ratiometric temperature measurement using these particles during photoinduced hyperthermia. This study suggests the use of plasmonic nanoparticles in the next generation "self-limiting" photothermal therapy.

Contribution of autofluorescence from intracellular proteins in multiphoton fluorescence lifetime imaging

Multiphoton fluorescence lifetime imaging microscopy (MPM-FLIM) is extensively proposed as a non-invasive optical method to study tissue metabolism. The approach is based on recording changes in the fluorescence lifetime attributed to metabolic co-enzymes, of which nicotinamide adenine dinucleotide (NADH) is of major importance. However, intrinsic tissue fluorescence is complex. Particularly when utilizing two-photon excitation, as conventionally employed in MPM. This increases the possibility for spectral crosstalk and incorrect assignment of the origin of the FLIM signal. Here we demonstrate that in keratinocytes, proteins such as keratin may interfere with the signal usually assigned to NADH in MPM-FLIM by contributing to the lifetime component at 1.5 ns. This is supported by a change in fluorescence lifetime distribution in KRT5- and KRT14-silenced cells. Altogether, our results suggest that the MPM-FLIM data originating from cellular autofluorescence is far more complex than previously suggested and that the contribution from other tissue constituents should not be neglected-changing the paradigm for data interpretation in this context.

Fluorescence-based thermometry for precise estimation of nanoparticle laser-induced heating in cancerous cells at nanoscale

Photothermal therapy (PTT) has attracted increasing interest as a complementary method to be used alongside conventional therapies. Despite a great number of studies in this field, only a few have explored how temperatures affect the outcome of the PTT at nanoscale. In this work, we study the necrosis/apoptosis process of cancerous cells that occurs during PTT, using a combination of local laser heating and nanoscale fluorescence thermometry techniques. The temperature distribution within a whole cell was evaluated using fluorescence lifetime imaging microscopy during laser-induced hyperthermia. For this, gold nanorods were utilized as nanoheaters. The local near-infrared laser illumination produces a temperature gradient across the cells, which is precisely measured by nanoscale thermometry. This allows one to optimize the PTT conditions by varying concentration of gold nanorods associated with cells and laser power density. During the PTT procedure, such an approach enables an accurate determination of the percentages of apoptotic and necrotic cells using 2D and 3D models. According to the performed cell experiments, the influence of temperature increase during the PTT on cell death mechanisms has been verified and determined. Our investigations can improve the understanding of the PTT mechanisms and increase its therapeutic efficiency while avoiding any side effects.

Improved temporal contrast of streak camera measurements with periodic shadowing

Periodic shadowing, a concept used in spectroscopy for stray light reduction, has been implemented to improve the temporal contrast of streak camera imaging. The capabilities of this technique are first proven by imaging elastically scattered picosecond laser pulses and are further applied to fluorescence lifetime imaging, where more accurate descriptions of fluorescence decay curves were observed. This all-optical approach can be adapted to various streak camera imaging systems, resulting in a robust technique to minimize space-charge induced temporal dispersion in streak cameras while maintaining temporal coverage and spatial information.

A Dual Fluorescence-Spin Label Probe for Visualization and Quantification of Target Molecules in Tissue by Multiplexed FLIM-EPR Spectroscopy

Simultaneous visualization and concentration quantification of molecules in biological tissue is an important though challenging goal. The advantages of fluorescence lifetime imaging microscopy (FLIM) for visualization, and electron paramagnetic resonance (EPR) spectroscopy for quantification are complementary. Their combination in a multiplexed approach promises a successful but ambitious strategy because of spin label-mediated fluorescence quenching. Here, we solved this problem and present the molecular design of a dual label (DL) compound comprising a highly fluorescent dye together with an EPR spin probe, which also renders the fluorescence lifetime to be concentration sensitive. The DL can easily be coupled to the biomolecule of choice, enabling in vivo and in vitro applications. This novel approach paves the way for elegant studies ranging from fundamental biological investigations to preclinical drug research, as shown in proof-of-principle penetration experiments in human skin ex vivo.

Design of an LCST-UCST-Like Thermoresponsive Zwitterionic Copolymer

Thermoresponsive polymers that possess both UCST- and LCST-like behaviors have generally been designed using diblock copolymers that are mostly composed of an LCST-like polymer and a UCST polymer. Herein, we prepared an LCST-UCST-type polymer composed of UCST-like thermoresponsive zwitterionic sulfabetaine methacrylate and nonthermoresponsive PEG methacrylate, ZB-PEG, by reversible addition-fragmentation chain transfer (RAFT) copolymerization. By adjusting the PEG composition, ZB-PEG formed a mesoglobule, a microglobule, and the dissociated states in phosphate-buffered saline (PBS). These states were found to be reversible via temperature control. Moreover, this behavior showed high reversibility and succeeded in stabilizing horseradish peroxidase (HRP) in the dilute condition. Such thermoresponsive ZB-PEG can be applied over a wide range of applications in biotechnology and other fields.

Photothermal therapy with silver nanoplates in HeLa cells studied by in situ fluorescence microscopy

Photothermal therapy (PTT) is a noninvasive treatment for cancer relying on the incorporation of NIR-light absorbing nanomaterials into cells, which upon illumination release heat causing thermally induced cell death. We prove that irradiation of aqueous suspensions of poly(vinylpyrrolidone)-coated silver nanoplates (PVPAgNP) or PVPAgNP in HeLa cells with red or NIR lasers causes a sizeable photothermal effect, which in cells can be visualized with the temperature sensing fluorophore Rhodamine B (RhB) using spinning disk confocal fluorescence microscopy or fluorescence lifetime imaging. Upon red-light irradiation of cells that were incubated with both, RhB and PVPAgNP at concentrations with no adverse effects on cell viability, a substantial heat release is detected. Initiation of cell death by photothermal effect is observed by positive signals of fluorescent markers for early and late apoptosis. Surprisingly, a new nanomaterial-assisted cell killing mode is operating when PVPAgNP-loaded HeLa cells are excited with moderate powers of fs-pulsed NIR light. Small roundish areas are generated with bright and fast (<1 ns) decaying emission, which expand fast and destroy the whole cell in seconds. This characteristic emission is assigned to efficient optical breakdown initiation around the strongly absorbing PVPAgNP leading to plasma formation that spreads fast through the cell.

Laser-Induced Single-Molecule Extraction and Detection in Aqueous Poly(N-isopropylacrylamide)/1-Butanol Solutions

We report photothermal phase separation of aqueous poly(N-isopropylacrylamide) (PNIPAM)/1-butanol (BuOH) solutions by focused 1064 nm laser irradiation and subsequent single microparticle formation in the solution. The single microparticle [diameter = ∼10 μm and volume = ∼picoliter (pL)] produced by laser irradiation was optically trapped by the incident 1064 nm laser beam, and this enabled us in situ Raman/fluorescence microspectroscopies of the particle. Raman spectroscopy demonstrated that the particle produced by laser irradiation was composed of PNIPAM and BuOH. In the presence of rhodamine B (RhB) in the solution, RhB was distributed from the water phase to the PNIPAM/BuOH microparticle produced by laser irradiation, as confirmed by fluorescence microspectroscopy. Laser-induced distribution/extraction of RhB to a single PNIPAM/BuOH microparticle was shown to be possible at the RhB concentration as low as 10^-14 mol/dm³, where the RhB fluorescence intensity from the particle showed a step-by-step increase by every ∼3 min laser irradiation. This is the first demonstration of laser-induced simultaneous extraction and detection of single RhB molecules in solution.

How Viscous Is the Solidlike Structure at the Interface of Ionic Liquids? A Study Using Total Internal Reflection Fluorescence Spectroscopy with a Fluorescent Molecular Probe Sensitive to High Viscosity

Aiming at the evaluation of the viscosity of the interfacial solidlike structure of ionic liquids (ILs), we performed total internal reflection fluorescence (TIRF) spectroscopy for N,N-diethyl-N'-phenyl-rhodamine (Ph-DER), a fluorescent probe that is sensitive to viscosity in a high-viscosity range. TIRF spectra at the glass interface of trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide (TOMAC4C4N), a hydrophobic IL, showed that the fluorescence intensity of Ph-DER increases with the decrease of the evanescence penetration depth, suggesting that there exists a high-viscosity region at the interface. In contrast, glycerol, which is a molecular liquid with a bulk viscosity similar to that of TOMAC4C4N, did not show such a fluorescence increase, supporting that the formation of a highly viscous solidlike structure at the interface is intrinsic to ILs. A model analysis suggested that the high viscous region at the glass interface of TOMAC4C4N is at least twice thicker than the ionic multilayers at the air interface, implying that the solid substrate enhances the ordering of the interfacial structure of ILs. The viscosity at the glass interface of TOMAC4C4N was found to be at least 40 times higher than that of the liquid bulk.

Cyclodextrin Cationic Polymer-Based Nanoassemblies to Manage Inflammation by Intra-Articular Delivery Strategies

Injectable nanobioplatforms capable of locally fighting the inflammation in osteoarticular diseases, by reducing the number of administrations and prolonging the therapeutic effect is highly challenging. β-Cyclodextrin cationic polymers are promising cartilage-penetrating candidates by intra-articular injection due to the high biocompatibility and ability to entrap multiple therapeutic and diagnostic agents, thus monitoring and mitigating inflammation. In this study, nanoassemblies based on poly-β-amino-cyclodextrin (PolyCD) loaded with the non-steroidal anti-inflammatory drug diclofenac (DCF) and linked by supramolecular interactions with a fluorescent probe (adamantanyl-Rhodamine conjugate, Ada-Rhod) were developed to manage inflammation in osteoarticular diseases. PolyCD@Ada-Rhod/DCF supramolecular nanoassemblies were characterized by complementary spectroscopic techniques including UV-Vis, steady-state and time-resolved fluorescence, DLS and ζ-potential measurement. Stability and DCF release kinetics were investigated in medium mimicking the physiological conditions to ensure control over time and efficacy. Biological experiments evidenced the efficient cellular internalization of PolyCD@Ada-Rhod/DCF (within two hours) without significant cytotoxicity in primary human bone marrow-derived mesenchymal stromal cells (hMSCs). Finally, polyCD@Ada-Rhod/DCF significantly suppressed IL-1β production in hMSCs, revealing the anti-inflammatory properties of these nanoassemblies. With these premises, this study might open novel routes to exploit original CD-based nanobiomaterials for the treatment of osteoarticular diseases.

Discriminating different grades of cervical intraepithelial neoplasia based on label-free phasor fluorescence lifetime imaging microscopy

This study proposed label-free fluorescence lifetime imaging and phasor analysis methods to discriminate different grades of cervical intraepithelial neoplasia (CIN). The human cervical tissue lesions associated with cellular metabolic abnormalities were detected by the status changes of important coenzymes in cells and tissues, reduced nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) and flavin adenine dinucleotide (FAD). Fluorescence lifetime imaging microscopy (FLIM) was used to study human cervical tissues, human cervical epithelial cells, and standard samples. Phasor analysis was applied to reveal the interrelation between the metabolic changes and cancer development, which can distinguish among different stages of cervical lesions from low risk to high risk. This approach also possessed high sensitivity, especially for healthy sites of CIN3 tissues, and indicated the dominance of the glycolytic pathway over oxidative phosphorylation in high-grade cervical lesions. This highly adaptive, sensitive, and rapid diagnostic tool exhibits a great potential for cervical precancer diagnosis.

Method to improve the tunable capacity of time-resolved encoding to a xanthene dye

Conventional organic dye encoding is limited by photo-bleaching and spectral overlap, thus restricting the number of distinguishable codes that can be used in practice. The utility of a single dye for increasing additional encoding capacity has yet to be explored. To this end, we firstly report a facile, flexible and green sustainable method to maximize the time-resolved encoding capacity of the xanthene red dye, eosin. By simply adjusting the concentration, pH and viscosity of the eosin solution, eleven distinguishable populations of fluorescence lifetimes were obtained with a short lifetime range of 1.0-3.4 ns, which in turn could increase the difficulty of duplication and provide extra high-level security protection. The results provide a facile strategy to increase the temporal multiplexing capacity, and may result in the reuse of existing organic dyes as lifetime-coded polymer microspheres in the fields of information security.

Widefield multifrequency fluorescence lifetime imaging using a two-tap complementary metal-oxide semiconductor camera with lateral electric field charge modulators

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.

Dual-functional fluorescent molecular rotor for endoplasmic reticulum microviscosity imaging during reticulophagy

A dual functional fluorescent molecular rotor was developed to trigger intracellular ER autophagy and quantify the local viscosity variations by FLIM imaging.