Super-resolution optical imaging: A comparison

A detailed review of genetically encodable RFPs and far-RFPs and their applications in advanced super-resolution imaging techniques

The red fluorescent proteins (RFPs) and far-red fluorescent proteins (far-RFPs) that are encoded genetically can emit fluorescence within the spectral ranges of 580-680 nm when exposed to the light of appropriate wavelengths. Unlike many RFPs derived from coral species, numerous far-RFPs are optimized synthetic constructs engineered from different orange or red-emitting progenitors. Various categories have been established for the available RFPs and far-red fluorescent proteins based on their photo-chemical profile, fluorescence mechanism, and switching kinetics. Fluorescent probes (FPs) derived from these classes are extensively utilized for labelling and visualizing in vivo and in vitro specimens. Traditional optical microscopy methods generate diffraction-limited, indistinct images owing to the restricted resolution capability of light ranging from 200 to 300 nm. Since 2005, super-resolution microscopy has been a topic of great interest due to its ability to achieve imaging at spatial resolutions of less than 100 nm. The 2014 Nobel Prize in Chemistry was awarded to Eric Betzig, Stefan Hell, and William E. Moerner for their contributions to demonstrating the effectiveness of genetically encodable fluorescent proteins in visualizing biological systems through super-resolution fluorescence microscopy. This review provides a concise overview of RFPs and far-RFPs, including the involvement of surrounding residues in chromophore intactness, stability, autocatalytic maturation and switching kinetics. All the chemical pathways proposed for photoactivation, photoconversion and photoswitching mechanisms are concisely reviewed. Subsequently, a comprehensive summary was provided regarding the various types of super-resolution techniques that are commonly employed, elucidating their underlying principles of operation, as well as the potential future applications of RFPs/far-RFPs in the field of biological imaging.

Split-Aperture Xolography - Linear Volumetric Photoactivation with Short Axial Dimension and Low out of Focus Excitation

Spatially confined photo-excitation with the lowest possible activation of the remaining volume is of central importance for high-resolution high-density optical data storage, fluorescence microscopy, 3D-lithography, and 3D-printing. Two-photon absorption (2PA) enables such applications yet leads to slow processing speed due to the underlying non-linear absorption process. Here, Split-Aperture Xolography (SAX), is introduced which uses stepwise excitation of dual-color responsive molecules to initiate a linear volumetric photo-reaction process that is up to several orders of magnitude more efficient than 2PA. The capabilities of SAX are investigated in a scenario study for focusing systems with high numerical aperture (NA) using a Python implementation of vectorial diffraction theory. The intersecting half-cones generated by the split illuminated entrance aperture of the objective reduce the axial focal spot size of the activation distribution by up to a factor of two compared to 2PA targeting the same electronic transition. A steep average decline of the activation probability with the fifth power away from focus is found for a wide range of directions. This is significantly better in comparison to 2PA and prevents that undesired out-of-focus excitation events sum-up with subsequent irradiations. This approach is expected to be advantageous for volumetric methods at the nanoscale.

Super-resolution algorithms for imaging FCS enhancement: A comparative study

Understanding the structure and dynamics of biological systems is often limited by the trade-off between spatial and temporal resolution. Imaging fluorescence correlation spectroscopy (ImFCS) is a powerful technique for capturing molecular dynamics with high temporal precision but remains diffraction limited. This constraint poses challenges for quantifying dynamics of subcellular structures like membrane-proximal cortical actin fibers. Computational super-resolution microscopy (CSRM) presents an accessible strategy for enhancing spatial resolution without specialized instrumentation, enabling compatibility with ImFCS. In this study, we evaluated various CSRM techniques, including super-resolution radial fluctuations, mean-shift super-resolution, and multiple signal classification imaging, using total internal reflection fluorescence datasets of actin fibers labeled with F-tractin-mApple. By combining structural masks from total internal reflection fluorescence and CSRM, we distinguished off-fiber, mixed, and on-fiber regions for region-specific diffusion analyses. Although all CSRM algorithms improve ImFCS data analysis, super-resolution radial fluctuations demonstrated superior performance in identifying cortical actin fibers, showing minimal variance in on-fiber diffusion coefficients. These findings establish a framework for integrating CSRM with ImFCS to achieve high-resolution spatial and dynamic characterization of subcellular structures from single measurements.

The Potential of Optical Technologies in Early Virus Detection; Prospects in Addressing Future Viral Outbreaks

The urgent need for sensitive, rapid, and reliable diagnostic methodologies to control and prevent life-threatening pandemic infectious disease, such as COVID-19, remains a critical priority. Timely and on-site detection of viral pathogens is essential for effective disease management and mitigation of societal disruptions. Recent advancements in optical diagnostic methods have positioned them at the forefront of healthcare diagnostics, offering high sensitivity and specificity as viable alternatives to conventional techniques such as the Polymerase Chain Reaction (PCR), which often suffer from time delays and limited accessibility in resource-constrained environments. This review elucidates the potential of various optical diagnostic techniques, highlighting their advantages over traditional methods. It encompasses a range of optical modalities, including fluorescence-based approaches, Raman spectroscopy (RS), Plasmonic techniques (e.g., surface plasmon resonance (SPR), localized SPR, (LSPR), surface-enhanced Raman spectroscopy (SERS), and surface-enhanced fluorescence (SEF)), super resolution microscopies (SRMs), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), and integrated platforms such as waveguides and molecularly imprinted polymer (MIP)-based biosensors. Additionally, the evolution of novel biosensors, particularly 5th and 6th generation biosensors, in healthcare and the challenges related to these technologies were discussed. This studies reviewed aims to advance the development of portable, sensitive, specific, and cost-effective point-of-care (POC) diagnostic devices for the rapid detection of viral pathogens.

Expansion microscopy reveals thylakoid organisation alterations due to genetic mutations and far-red light acclimation

The thylakoid membrane is the site of the light-dependent reactions of photosynthesis. It is a continuous membrane, folded into grana stacks and the interconnecting stroma lamellae. The CURVATURE THYLAKOID1 (CURT1) protein family is involved in the folding of the membrane into the grana stacks. The thylakoid membrane remodels its architecture in response to light conditions, but its 3D organisation and dynamics remain incompletely understood. To resolve these details, an imaging technique is needed that provides high-resolution 3D images in a high-throughput manner. Recently, we have used expansion microscopy, a technique that meets these criteria, to visualise the thylakoid membrane isolated from spinach. Here, we show that this protocol can also be used to visualise enveloped spinach chloroplasts. Additionally, we present an improved protocol for resolving the thylakoid structure of Arabidopsis thaliana. Using this protocol, we show the changes in thylakoid architecture in response to long-term far-red light acclimation and due to knocking out CURT1A. We show that far-red light acclimation results in higher grana stacks that are packed closer together. In addition, the distance between stroma lamellae, which are wrapped around the grana, decreases. In the curt1a mutant, grana have an increased diameter and height, and the distance between grana is increased. Interestingly, in this mutant, the stroma lamellae occasionally approach the grana stacks from the top. These observations show the potential of expansion microscopy to study the thylakoid membrane architecture.

Non-Invasive Laser Surgery With Deep Operating Depth Using Multibeam Interference

Purpose

Laser surgery can use photo-chemical, photo-thermal, photo-ablative, and photo-mechanical effects to treat various tissues in the human body, and has unique advantages of extremely high precision, non-invasive penetration, and fast operation speed. However, at present, the effective penetration depth of directly illuminating light in the body is only several millimeters. Therefore, increasing the safe operating depth for non-invasive laser surgery will have important, widespread, and irreplaceable applications in the future.

Methods

The method is based on improving a recently emerged technique. Its principle involves using a negative dispersion device to broaden the width of the short light pulse first. Then, after the pulse enters the body, as its peak intensity is reduced, the skin and healthy tissues in the laser propagation path cannot be injured. Meanwhile, since body tissues have positive dispersion, the broadened width of the laser pulse will be shortened back. When the broadened pulse is completely shortened, a thin inner light layer with high intensity will be formed in the body and used as a scalpel to treat target tissue.

Results

The theoretical calculation results have shown that the designed apparatus has excellent performance. Its safe non-invasive operating depth can be more than 70 millimeters with the possibility of up to 130 millimeters. Surgery precisions are around 1 micron transversely and about 1 millimeter longitudinally in theory.

Conclusion

An improved method of non-invasive laser surgery with deep operation depth has been investigated theoretically. The calculations show that the designed apparatus has excellent performance. The proposed method depends on two well-known physical phenomena: light pulse broadening and shortening caused by optical negative and positive dispersions, and thus has solid basis. The developed method will have important, widespread and irreplaceable applications in the medical surgery field.

Fluorescence super-resolution microscopy via fluctuation-based multi-route synergy

Fluorescence fluctuation-based super-resolution microscopy (FF-SRM) is an economical and widely applicable technique that significantly enhances the spatial resolution of fluorescence imaging by capitalizing on fluorescence intermittency. However, each variant of FF-SRM imaging has inherent limitations. This study proposes a super-resolution reconstruction strategy (synSRM) by synergizing multiple variants of the FF-SRM approach to address the limitations and achieve high-quality and high-resolution imaging. The simulation and experimental results demonstrate that, compared to images reconstructed using single FF-SRM algorithms, by selecting suitable synSRM routes according to various imaging conditions, further improvements of the spatial resolution and image reconstruction quality can be obtained for super-resolution fluorescence imaging.

Deep SBP+ 2.0: a physics-driven generation capability enhanced framework to reconstruct a space-bandwidth product expanded image from two image shots

The space-bandwidth product (SBP) limitation makes it difficult to obtain an image with both a high spatial resolution and a large field of view (FoV) through commonly used optical imaging systems. Although FoV and spectrum stitch provide solutions for SBP expansion, they rely on spatial and spectral scanning, which lead to massive image captures and a low processing speed. To solve the problem, we previously reported a physics-driven deep SBP-expanded framework (Deep SBP+) [J. Opt. Soc. Am. A40, 833 (2023)JOAOD60740-323210.1364/JOSAA.480920]. Deep SBP+ can reconstruct an image with both high spatial resolution and a large FoV from a low-spatial-resolution image in a large FoV and several high-spatial-resolution images in sub-FoVs. In physics, Deep SBP+ reconstructs the convolution kernel between the low- and high-spatial-resolution images and improves the spatial resolution through deconvolution. But Deep SBP+ needs multiple high-spatial-resolution images in different sub-FoVs, inevitably complicating the operations. To further reduce the image captures, we report an updated version of Deep SBP+ 2.0, which can reconstruct an SBP expanded image from a low-spatial-resolution image in a large FoV and another high-spatial-resolution image in a sub-FoV. Different from Deep SBP+, the assumption that the convolution kernel is a Gaussian distribution is added to Deep SBP+ 2.0 to make the kernel calculation simple and in line with physics. Moreover, improved deep neural networks have been developed to enhance the generation capability. Proven by simulations and experiments, the receptive field is analyzed to prove that a high-spatial-resolution image in the sub-FoV can also guide the generation of the entire FoV. Furthermore, we also discuss the requirement of the sub-FoV image to obtain an SBP-expanded image of high quality. Considering its SBP expansion capability and convenient operation, the updated Deep SBP+ 2.0 can be a useful tool to pursue images with both high spatial resolution and a large FoV.

Converting evanescent waves into propagating waves by hyper-hemi-microsphere

Hyper-hemi-microspheres (HHMS) have shown promise in enhancing super-resolution imaging when combined with conventional optical microscopy. To offer actionable guidance for optimizing HHMS and hold broad applicability in the field of super-resolution imaging, the mechanism underpinning the enhanced imaging facilitated by HHMS is revealed by deriving the conversion and transmission conditions for evanescent waves. This is achieved by elucidating the intricate interplay between evanescent wave conversion and factors including refractive index, thickness, and surroundings of HHMS. Using the finite-difference time-domain (FDTD) method, influences of various HHMS properties on the conversion and transmission process are analyzed in detail. To fully harness the potential of HHMS in super-resolution imaging, the immersion conditions are elucidated.

Proteus mirabilis biofilm expansion microscopy yields over 4-fold magnification for super-resolution of biofilm structure and subcellular DNA organization

Bacterial biofilms form when bacteria attach to surfaces and generate an extracellular matrix that embeds and stabilizes a growing community. Detailed visualization and quantitative analysis of biofilm architecture by optical microscopy are limited by the law of diffraction. Expansion Microscopy (ExM) is a novel Super-Resolution technique where specimens are physically enlarged by a factor of ∼4, prior to observation by conventional fluorescence microscopy. ExM requires homogenization of rigid constituents of biological components by enzymatic digestion. We developed an ExM approach capable of expanding 48-h old Proteus mirabilis biofilms 4.3-fold (termed PmbExM), close to the theoretic maximum expansion factor without gross shape distortions. Our protocol, based on lytic and glycoside-hydrolase enzymatic treatments, degrades rigid components in bacteria and extracellular matrix. Our results prove PmbExM to be a versatile and easy-to-use Super-Resolution approach for enabling studies of P. mirabilis biofilm architecture, assembly, and even intracellular features, such as DNA organization.

Laser Beam Self-Focusing in Silicon at an Absorbed Wavelength by a Vortex Beam in the Same Wavelength

In this research, we present a novel approach to achieving super-resolution in silicon using the plasma dispersion effect (PDE) that temporarily controls the complex refractive index of matter. By employing a laser vortex pump beam, which is absorbed in the silicon, we can shape the complex refractive index as a gradient index (GRIN) lens, enabling the focusing of a laser probe beam within the material. Our study introduces a single beam at a wavelength of 775 nm for both the pump and the probe beams, offering tunable focusing capabilities and the potential to attain higher spatial resolution. These findings hold significant promise for applications in nanoelectronics and integrated circuit failure analysis, paving the way for advanced semiconductor imaging and analysis techniques.

An mTurq2-Col4a1 mouse model allows for live visualization of mammalian basement membrane development

Basement membranes (BMs) are specialized sheets of extracellular matrix that underlie epithelial and endothelial tissues. BMs regulate the traffic of cells and molecules between compartments, and participate in signaling, cell migration, and organogenesis. The dynamics of mammalian BMs, however, are poorly understood, largely due to a lack of models in which core BM components are endogenously labeled. Here, we describe the mTurquoise2-Col4a1 mouse in which we fluorescently tag collagen IV, the main component of BMs. Using an innovative planar-sagittal live imaging technique to visualize the BM of developing skin, we directly observe BM deformation during hair follicle budding and basal progenitor cell divisions. The BM's inherent pliability enables dividing cells to remain attached to and deform the BM, rather than lose adhesion as generally thought. Using FRAP, we show BM collagen IV is extremely stable, even during periods of rapid epidermal growth. These findings demonstrate the utility of the mTurq2-Col4a1 mouse to shed new light on mammalian BM developmental dynamics.

Enhancing axial localization with wavefront control

Enhancing the ability to resolve axial details is crucial in three-dimensional optical imaging. We provide experimental evidence showcasing the ultimate precision achievable in axial localization using vortex beams. For Laguerre-Gauss (LG) beams, this remarkable limit can be attained with just a single intensity scan. This proof-of-principle demonstrates that microscopy techniques based on LG vortex beams can potentially benefit from the introduced quantum-inspired superresolution protocol.

A Window into Mammalian Basement Membrane Development: Insights from the mTurq2-Col4a1 Mouse Model

Basement membranes (BMs) are specialized sheets of extracellular matrix that underlie epithelial and endothelial tissues. BMs regulate traffic of cells and molecules between compartments, and participate in signaling, cell migration and organogenesis. The dynamics of mammalian BMs, however, are poorly understood, largely due to a lack of models in which core BM components are endogenously labelled. Here, we describe the mTurquoise2-Col4a1 mouse, in which we fluorescently tag collagen IV, the main component of BMs. Using an innovative Planar-Sagittal live imaging technique to visualize the BM of developing skin, we directly observe BM deformation during hair follicle budding and basal progenitor cell divisions. The BM's inherent pliability enables dividing cells to remain attached to and deform the BM, rather than lose adhesion as generally thought. Using FRAP, we show BM collagen IV is extremely stable, even during periods of rapid epidermal growth. These findings demonstrate the utility of the mTurq2-Col4a1 mouse to shed new light on mammalian BM developmental dynamics.

Microlens-Assisted Light-Scattering Imaging of Plasmonic Nanoparticles at the Single Particle Level

We present a microlens-assisted imaging approach to record the scattering light of plasmonic nanoparticles at the single particle level. The microlens can significantly enhance the backscattering of visible light from individual plasmonic nanoparticles by several dozen folds, and single gold nanoparticles with a diameter as low as 60 nm can be imaged under a conventional optical microscope. This can benefit from a significant increase in the scattering intensity afforded by the microlens, meaning that the imaging of gold nanoparticles at a high temporal resolution (up to 5000 Hz) can be achieved, which is fast enough to record single particle adhesion events on the substrate. This research presents a fast and efficient means of acquiring scattering light from plasmonic nanoparticles, which has great potential to develop plasmonic nanoparticle-based biosensors and investigate a wide range of plasmonic nanoparticle-based fast interaction processes.

Phase-only steerable photonic nanojets

We demonstrate numerically the feasibility of axial and angular control of the position of a photonic nanojet (PNJ) by lossless phase-only modulation of a fixed Gaussian beam illuminating a fixed 2D circular homogeneous dielectric micro-lens. We furthermore demonstrate that our phase-only modality can be used to calibrate and improve the confinement of PNJ generation.

Deep SBP+: breaking through the space-bandwidth product limit based on a physical-driven cycle constraint framework

To obtain an image with both high spatial resolution and a large field of view (FoV), we designed a deep space-bandwidth product (SBP)-expanded framework (Deep SBP+). Combining a single-captured low-spatial-resolution image with a large FoV and a few captured high-spatial-resolution images in sub-FoVs, an image with both high spatial resolution and a large FoV can be reconstructed via Deep SBP+. The physical model-driven Deep SBP+ reconstructs the convolution kernel as well as up-samples the low-spatial resolution image in a large FoV without relying on any external datasets. Compared to conventional methods relying on spatial and spectral scanning with complicated operations and systems, the proposed Deep SBP+ can reconstruct high-spatial-resolution and large-FoV images with much simpler operations and systems as well as faster speed. Since the designed Deep SBP+ breaks through the trade-off of high spatial resolution and large FoV, it is a promising tool for photography and microscopy.

A computational two-photon fluorescence approach for revealing label-free the 3D image of viruses and bacteria

Current solutions for bacteria and viruses identification are based on time-consuming technics with complex preparation procedures. In the present work, we revealed label-free the presence of free viral particles and bacteria with a computational two-photon fluorescence (C-TPF) strategy. Six bacteria were tested: Escherichia coli, Staphylococcus epidermidis, Proteus vulgaris, Pseudomonas fluorescens, Bacillus subtilis, and Clostridium perfringens. The two families of viral particles were the herpes virus with the cytomegalovirus (CMV, 300 nm of diameter) and the coronavirus with the SARS-CoV-2 (100 nm of diameter). The instrumental and computational pipeline FAMOUS optimized the produced 3D images. The origin of the fluorescence emission was discussed for bacteria regarding to their two-photon excitation spectra and attributed to the metabolic indicators (FAD and NADH). The optical and computational strategy constitute a new approach for imaging label-free viral particles and bacteria and paves the way to a new understanding of viral or bacterial ways of infection.

Steerable photonic jet for super-resolution microscopy

A promising technique in optical super-resolution microscopy is the illumination of the sample by a highly localized beam, a photonic jet (also called photonic nanojet). We propose a method of computation of incident field amplitude and phase profiles that produce photonic jets at desired locations in the near field after interaction with a fixed micro-scale dielectric lens. We also describe a practical way of obtaining the incident field profiles using spatial light modulators. We expect our photonic jet design method to work for a wide range of lens shapes, and we demonstrate its application numerically using two-dimensional micro-lenses of circular and square cross-sections. We furthermore offer a theoretical analysis of the resolution of photonic jet design, predicting among other that a larger lens can produce a narrower photonic jet. Finally, we give both theoretical and numerical evidence that the waist width of the achieved designed jets is increasing linearly and slowly over a large interval of radial distances. With uniform plane wave illumination, the circular two-dimensional micro-lens produces a similar-sized jet at a fixed radial distance, while the square lens does not form a jet at all. We expect our steerable optical photonic jet probe to enable highly localized adaptive real-time measurements and drive advances in super-resolution optical microscopy and scatterometry, as well as fluorescence and Raman microscopy. Our relatively weak peak jet intensity allows application in biology and health sciences, which require high resolution imaging without damaging the sample bio-molecules.

Microlens-assisted microscopy for biology and medicine

The addition of dielectric transparent microlens in the optical scheme is an effective and at the same time simple and inexpensive way to increase the resolution of a light microscope. For these purposes, spherical and cylindrical microlenses with a diameter of 1-100 μm are usually used. The microlens focuses the light into a narrow beam called a photonic nanojet. An enlarged virtual image is formed, which is captured by the objective of the light microscope. In addition to microscopy, the microlenses are successfully applied to amplify optical signals, increase the trapping force of optical tweezers and are used in microsurgery. This review considers the design and principle of microlens-assisted microscopes. Taking into account the advantages of the super-resolution optical methods for research in life science, the examples of the use of the microlenses in biomedical practice are discussed in detail.

Inverse propagation method for evaluation of super-resolution granted by dielectric microparticles

In this work we report a theoretical study of the lateral resolution granted by a simple glass microcylinder. In this 2D study, we had in mind the 3D analogue-a microsphere whose ability to form a deeply subwavelength and strongly magnified image of submicrometer objects has been known since 2011. Conventionally, the microscope in which such an image is observed is tuned to see the areas behind the microsphere. This corresponds to the location of the virtual source formed by the microsphere at a distance longer than the distance of the real source to the miscroscope. Recently, we theoretically found a new scenario of super-resolution, when the virtual source is formed in the wave beam transmitted through the microsphere. However, in this work we concentrated on the case when the super-resolution is achieved in the impractical imaging system, in which the microscope objective lens is replaced by a microlens located at a distance smaller than the Rayleigh range. The present paper theoretically answers an important question: Which scenario of far-field nanoimaging by a microsphere grants the finest spatial resolution at very large distances? We found that the novel scenario (corresponding to higher refractive indices) promises further enhancement of the resolution.

Finding Needles in a Haystack with Light: Resolving the Microcircuitry of the Brain with Fluorescence Microscopy

To understand the microcircuitry of the brain, the anatomical and functional connectivity among neurons must be resolved. One of the technical hurdles to achieving this goal is that the anatomical connections, or synapses, are often smaller than the diffraction limit of light and thus are difficult to resolve by conventional microscopy, while the microcircuitry of the brain is on the scale of 1 mm or larger. To date, the gold standard method for microcircuit reconstruction has been electron microscopy (EM). However, despite its rapid development, EM has clear shortcomings as a method for microcircuit reconstruction. The greatest weakness of this method is arguably its incompatibility with functional and molecular analysis. Fluorescence microscopy, on the other hand, is readily compatible with numerous physiological and molecular analyses. We believe that recent advances in various fluorescence microscopy techniques offer a new possibility for reliable synapse detection in large volumes of neural circuits. In this minireview, we summarize recent advances in fluorescence-based microcircuit reconstruction. In the same vein as these studies, we introduce our recent efforts to analyze the long-range connectivity among brain areas and the subcellular distribution of synapses of interest in relatively large volumes of cortical tissue with array tomography and superresolution microscopy.

Development of Planar Illumination Strategies for Solving Mysteries in the Sub-Cellular Realm

Optical microscopy has vastly expanded the frontiers of structural and functional biology, due to the non-invasive probing of dynamic volumes in vivo. However, traditional widefield microscopy illuminating the entire field of view (FOV) is adversely affected by out-of-focus light scatter. Consequently, standard upright or inverted microscopes are inept in sampling diffraction-limited volumes smaller than the optical system's point spread function (PSF). Over the last few decades, several planar and structured (sinusoidal) illumination modalities have offered unprecedented access to sub-cellular organelles and 4D (3D + time) image acquisition. Furthermore, these optical sectioning systems remain unaffected by the size of biological samples, providing high signal-to-noise (SNR) ratios for objective lenses (OLs) with long working distances (WDs). This review aims to guide biologists regarding planar illumination strategies, capable of harnessing sub-micron spatial resolution with a millimeter depth of penetration.

Design, Analysis and Experiment of a Bridge-Type Piezoelectric Actuator for Infrared Image Stabilization

Piezoelectric actuators are widely used in the optical field due to their high precision, compact structure, flexible design, and fast response. This paper presents a novel piezoelectric actuator with a bridge-type mechanism, which can be used to stabilize the images of an infrared imaging system. The bridge amplification mechanism is used to amplify the actuation displacement, and its structural parameters are optimized by the response surface method. The control strategy of the image stabilization system is formulated, and the overall structure of the infrared image stabilization system is designed according to the principle of image stabilization and the control strategy. The prototype was fabricated and verified by a series of experiments. In the test, the laminated piezoelectric ceramics are used as the driving element, and its maximum output displacement was about 17 μm under a voltage of 100 V. Firstly, the performance of the piezoelectric amplification mechanism was tested, and the maximum displacement of the piezoelectric micro-motion mechanism was 115 μm. The displacement amplification ratio of the mechanism was 5.7. Then, the step distance and response time of the micro-displacement mechanism were measured by inputting the stepping signal. When the input voltage increased to 3 V, 5 V, and 7 V, the stepping displacements of the mechanism were 2.4 μm, 4.1 μm, and 5.8 μm. Finally, the image stabilization effect of the designed mechanism was verified by imaging timing control and feedback signal processing.

Super-Resolution Fluorescence Microscopy Methods for Assessing Mouse Biology

Super-resolution (diffraction unlimited) microscopy was developed 15 years ago; the developers were awarded the Nobel Prize in Chemistry in recognition of their work in 2014. Super-resolution microscopy is increasingly being applied to diverse scientific fields, from single molecules to cell organelles, viruses, bacteria, plants, and animals, especially the mammalian model organism Mus musculus. In this review, we explain how super-resolution microscopy, along with fluorescence microscopy from which it grew, has aided the renaissance of the light microscope. We cover experiment planning and specimen preparation and explain structured illumination microscopy, super-resolution radial fluctuations, stimulated emission depletion microscopy, single-molecule localization microscopy, and super-resolution imaging by pixel reassignment. The final section of this review discusses the strengths and weaknesses of each super-resolution technique and how to choose the best approach for your research. © 2021 The Authors. Current Protocols published by Wiley Periodicals LLC.

Differential Polarization Imaging of Plant Cells. Mapping the Anisotropy of Cell Walls and Chloroplasts

Modern light microscopy imaging techniques have substantially advanced our knowledge about the ultrastructure of plant cells and their organelles. Laser-scanning microscopy and digital light microscopy imaging techniques, in general—in addition to their high sensitivity, fast data acquisition, and great versatility of 2D–4D image analyses—also opened the technical possibilities to combine microscopy imaging with spectroscopic measurements. In this review, we focus our attention on differential polarization (DP) imaging techniques and on their applications on plant cell walls and chloroplasts, and show how these techniques provided unique and quantitative information on the anisotropic molecular organization of plant cell constituents: (i) We briefly describe how laser-scanning microscopes (LSMs) and the enhanced-resolution Re-scan Confocal Microscope (RCM of Confocal.nl Ltd. Amsterdam, Netherlands) can be equipped with DP attachments—making them capable of measuring different polarization spectroscopy parameters, parallel with the ‘conventional’ intensity imaging. (ii) We show examples of different faces of the strong anisotropic molecular organization of chloroplast thylakoid membranes. (iii) We illustrate the use of DP imaging of cell walls from a variety of wood samples and demonstrate the use of quantitative analysis. (iv) Finally, we outline the perspectives of further technical developments of micro-spectropolarimetry imaging and its use in plant cell studies.

Prediction of Neural Diameter From Morphology to Enable Accurate Simulation

Accurate neuron morphologies are paramount for computational model simulations of realistic neural responses. Over the last decade, the online repository NeuroMorpho.Org has collected over 140,000 available neuron morphologies to understand brain function and promote interaction between experimental and computational research. Neuron morphologies describe spatial aspects of neural structure; however, many of the available morphologies do not contain accurate diameters that are essential for computational simulations of electrical activity. To best utilize available neuron morphologies, we present a set of equations that predict dendritic diameter from other morphological features. To derive the equations, we used a set of NeuroMorpho.org archives with realistic neuron diameters, representing hippocampal pyramidal, cerebellar Purkinje, and striatal spiny projection neurons. Each morphology is separated into initial, branching children, and continuing nodes. Our analysis reveals that the diameter of preceding nodes, Parent Diameter, is correlated to diameter of subsequent nodes for all cell types. Branching children and initial nodes each required additional morphological features to predict diameter, such as path length to soma, total dendritic length, and longest path to terminal end. Model simulations reveal that membrane potential response with predicted diameters is similar to the original response for several tested morphologies. We provide our open source software to extend the utility of available NeuroMorpho.org morphologies, and suggest predictive equations may supplement morphologies that lack dendritic diameter and improve model simulations with realistic dendritic diameter.

Towards a Quantitative Single Particle Characterization by Super Resolution Microscopy: From Virus Structures to Antivirals Design

In the last year the COVID19 pandemic clearly illustrated the potential threat that viruses pose to our society. The characterization of viral structures and the identification of key proteins involved in each step of the cycle of infection are crucial to develop treatments. However, the small size of viruses, invisible under conventional fluorescence microscopy, make it difficult to study the organization of protein clusters within the viral particle. The applications of super-resolution microscopy have skyrocketed in the last years, converting this group into one of the leading techniques to characterize viruses and study the viral infection in cells, breaking the diffraction limit by achieving resolutions up to 10 nm using conventional probes such as fluorescent dyes and proteins. There are several super-resolution methods available and the selection of the right one it is crucial to study in detail all the steps involved in the viral infection, quantifying and creating models of infection for relevant viruses such as HIV-1, Influenza, herpesvirus or SARS-CoV-1. Here we review the use of super-resolution microscopy (SRM) to study all steps involved in the viral infection and antiviral design. In light of the threat of new viruses, these studies could inspire future assays to unveil the viral mechanism of emerging viruses and further develop successful antivirals against them.

Wetting of electrospun nylon-11 fibers and mats

Wetting of electrospun mats plays a huge role in tissue engineering and filtration applications. However, it is challenging to trace the interrelation between the wetting of individual nano-sized fibers and the macroscopic electrospun mat. Here we measured the wetting of different nylon-11 samples – solution-cast films, electrospun fibers deposited onto a substrate, and free-standing mats. With electrospun nylon-11 on aluminium foil, we traced the dependence of the wetting contact angle on the fibers' surface density (substrate coverage). When the coverage was low, the contact angle increased almost linearly with it. At ∼17–20% coverage, the contact angle achieved its maximum of 124 ± 7°, which matched the contact angle of a non-woven electrospun mat, 126 ± 2°. Our results highlight the importance of the outermost layer of fibers for the wetting of electrospun mats.

When the surface density of electrospun nylon-11 fibers on aluminium increases, it causes a two-stage change in the wetting behaviour.

Optical and magnetic resonance imaging approaches for investigating the tumour microenvironment: state-of-the-art review and future trends

The tumour microenvironment (TME) strongly influences tumorigenesis and metastasis. Two of the most characterized properties of the TME are acidosis and hypoxia, both of which are considered hallmarks of tumours as well as critical factors in response to anticancer treatments. Currently, various imaging approaches exist to measure acidosis and hypoxia in the TME, including magnetic resonance imaging (MRI), positron emission tomography and optical imaging. In this review, we will focus on the latest fluorescent-based methods for optical sensing of cell metabolism and MRI as diagnostic imaging tools applied both in vitro and in vivo. The primary emphasis will be on describing the current and future uses of systems that can measure intra- and extra-cellular pH and oxygen changes at high spatial and temporal resolution. In addition, the suitability of these approaches for mapping tumour heterogeneity, and assessing response or failure to therapeutics will also be covered.

Large Stokes-shift bioorthogonal probes for STED, 2P-STED and multi-color STED nanoscopy

Synthesis and multiple STED imaging applications of four, red-emitting (610-670 nm), tetrazine-functionalized fluorescent probes (CBRD = Chemical Biology Research group Dye 1-4) with large Stokes-shift is presented. Present studies revealed the super-resolution microscopy applicability of the probes as demonstrated through bioorthogonal labeling scheme of cytoskeletal proteins actin and keratin-19, and mitochondrial protein TOMM20. Furthermore, super-resolved images of insulin receptors in live-cell bioorthogonal labeling schemes through a genetically encoded cyclooctynylated non-canonical amino acid are also presented. The large Stokes-shifts and the wide spectral bands of the probes enabled the use of two common depletion lasers (660 nm and 775 nm). The probes were also found suitable for super-resolution microscopy in combination with two-photon excitation (2P-STED) resulting in improved spatial resolution. One of the dyes was also used together with two commercial dyes in the three-color STED imaging of intracellular structures.

Preparation, Scanning and Analysis of Duckweed Using X-Ray Computed Microtomography

Quantification of anatomical and compositional features underpins both fundamental and applied studies of plant structure and function. Relatively few non-invasive techniques are available for aquatic plants. Traditional methods such as sectioning are low-throughput and provide 2-dimensional information. X-ray Computed Microtomography (μCT) offers a non-destructive method of three dimensional (3D) imaging in planta, but has not been widely used for aquatic species, due to the difficulties in sample preparation and handling. We present a novel sample handling protocol for aquatic plant material developed for μCT imaging, using duckweed plants and turions as exemplars, and compare the method against existing approaches. This technique allows for previously unseen 3D volume analysis of gaseous filled spaces, cell material, and sub-cellular features. The described embedding method, utilizing petrolatum gel for sample mounting, was shown to preserve sample quality during scanning, and to display sufficiently different X-ray attenuation to the plant material to be easily differentiated by image analysis pipelines. We present this technique as an improved method for anatomical structural analysis that provides novel cellular and developmental information.

Unraveling the Nanoscopic Organization and Function of Central Mammalian Presynapses With Super-Resolution Microscopy

The complex, nanoscopic scale of neuronal function, taking place at dendritic spines, axon terminals, and other minuscule structures, cannot be adequately resolved using standard, diffraction-limited imaging techniques. The last couple of decades saw a rapid evolution of imaging methods that overcome the diffraction limit imposed by Abbe's principle. These techniques, including structured illumination microscopy (SIM), stimulated emission depletion (STED), photo-activated localization microscopy (PALM), and stochastic optical reconstruction microscopy (STORM), among others, have revolutionized our understanding of synapse biology. By exploiting the stochastic nature of fluorophore light/dark states or non-linearities in the interaction of fluorophores with light, by using modified illumination strategies that limit the excitation area, these methods can achieve spatial resolutions down to just a few tens of nm or less. Here, we review how these advanced imaging techniques have contributed to unprecedented insight into the nanoscopic organization and function of mammalian neuronal presynapses, revealing new organizational principles or lending support to existing views, while raising many important new questions. We further discuss recent technical refinements and newly developed tools that will continue to expand our ability to delve deeper into how synaptic function is orchestrated at the nanoscopic level.

Super-Resolution without Imaging: Library-Based Approaches Using Near-to-Far-Field Transduction by a Nanophotonic Structure

Super-resolution imaging is often viewed in terms of engineering narrow point spread functions, but nanoscale optical metrology can be performed without real-space imaging altogether. In this paper, we investigate how partial knowledge of scattering nanostructures enables extraction of nanoscale spatial information from far-field radiation patterns. We use principal component analysis to find patterns in calibration data and use these patterns to retrieve the position of a point source of light. In an experimental realization using angle-resolved cathodoluminescence, we retrieve the light source position with an average error below λ/100. The patterns found by principal component analysis reflect the underlying scattering physics and reveal the role the scattering nanostructure plays in localization success. The technique described here is highly general and can be applied to gain insight into and perform subdiffractive parameter retrieval in various applications.

100th Anniversary of Macromolecular Science Viewpoint: Enabling Advances in Fluorescence Microscopy Techniques

In the past few decades there has been a revolution in the field of optical microscopy with emerging capabilities such as super-resolution and single-molecule fluorescence techniques. Combined with the classical advantages of fluorescence imaging, such as chemical labeling specificity, and noninvasive sample preparation and imaging, these methods have enabled significant advances in our polymer community. This Viewpoint discusses several of these capabilities and how they can uniquely offer information where other characterization techniques are limited. Several examples are highlighted that demonstrate the ability of fluorescence microscopy to understand key questions in polymer science such as single-molecule diffusion and orientation, 3D nanostructural morphology, and interfacial and multicomponent dynamics. Finally, we briefly discuss opportunities for further advances in techniques that may allow them to make an even greater contribution in polymer science.

Intensity-Based Axial Localization at the Quantum Limit

We derive fundamental precision bounds for single-point axial localization. For Gaussian beams, this ultimate limit can be achieved with a single intensity scan, provided the camera is placed at one of two optimal transverse detection planes. Hence, for axial localization there is no need of more complicated detection schemes. The theory is verified with an experimental demonstration of axial resolution 3 orders of magnitude below the classical depth of focus.