Optical Clearing Research Articles

ROCKETS - a novel one-for-all toolbox for light sheet microscopy in drug discovery.

Advancing novel immunotherapy strategies requires refined tools in preclinical research to thoroughly assess drug targets, biodistribution, safety, and efficacy. Light sheet fluorescence microscopy (LSFM) offers unprecedented fast volumetric ex vivo imaging of large tissue samples in high resolution. Yet, to date laborious and unstandardized tissue processing procedures have limited throughput and broader applications in immunological research. Therefore, we developed a simple and harmonized protocol for processing, clearing and imaging of all mouse organs and even entire mouse bodies. Applying this Rapid Optical Clearing Kit for Enhanced Tissue Scanning (ROCKETS) in combination with LSFM allowed us to comprehensively study the in vivo biodistribution of an antibody targeting Epithelial Cell Adhesion Molecule (EpCAM) in 3D. Quantitative high-resolution scans of whole organs did not only reveal known EpCAM expression patterns but, importantly, uncovered several new EpCAM-binding sites. We identified gustatory papillae of the tongue, choroid plexi in the brain and duodenal papillae as previously unanticipated locations of high EpCAM expression. Subsequently, we confirmed high EpCAM expression also in human tongue and duodenal specimens. Choroid plexi and duodenal papillae may be considered as particularly sensitive sites due to their importance for liquor production or as critical junctions draining bile and digestive pancreatic enzymes into the small bowel, respectively. These newly gained insights appear highly relevant for clinical translation of EpCAM-addressing immunotherapies. Thus, ROCKETS in combination with LSFM may help to set new standards for preclinical evaluation of immunotherapeutic strategies. In conclusion, we propose ROCKETS as an ideal platform for a broader application of LSFM in immunological research optimally suited for quantitative co-localization studies of immunotherapeutic drugs and defined cell populations in the microanatomical context of organs or even whole mice.

Influence of laser beam aberrations compensation and spot size on the transmittance in native and optically cleared skeletal muscles

Light propagation and penetration inside tissues highly affect the optical imaging of biological tissues. Two major factors influence that; the first is associated with the dense scattering properties of tissues. Consequently, optical clearing (OC) methods have been developed to reduce tissue scattering by matching the tissue layers’ refractive indices via different protocols. The second factor is related to the illuminating wavefront and the size of the incident light beam. The present work monitored the optical transmittance of skeletal muscles after applying different OC approaches (physical OC using 99%-glycerol immersion and photothermal OC using IR-laser irradiation). First, the optical transmittance of the samples before and after the two OC procedures were compared, revealing a transmittance increase of 300% and 20%. Then, the laser beam wavefront aberrations were compensated in real-time by utilizing an active-adaptive Shack-Hartmann wavefront sensor system to provide an ideal illumination wavefront. Finally, the transmittance of the samples was compared using uncompensated and compensated laser wavefronts providing a 35% increase in the transmittance after aberrations compensation. Moreover, the aberration-free incident laser beam’s transmittance with different spot diameters was investigated. The results revealed that the larger beam diameter provided higher transmittance, hence higher optical penetration within the tissue.

Tet-Regulated Expression and Optical Clearing for In Vivo Visualization of Genetically Encoded Chimeric dCas9/Fluorescent Protein Probes.

The catalytically inactive mutant of Cas9 (dCas9) endonuclease has multiple biomedical applications, with the most useful being the activation/repression of transcription. dCas9 family members are also emerging as potential experimental tools for gene mapping at the level of individual live cells and intact tissue. We performed initial testing on a set of tools for Cas9-mediated visualization of nuclear compartments. We investigated doxycycline (Dox)-inducible (Tet-On) intracellular distribution of constructs encoding dCas9 orthologs from St. thermophilus (St) and N. meningitides (Nm) fused with EGFP and mCherry fluorescent proteins (FP) in human A549 cells. We also studied time-dependent expression of these chimeric fluorescent constructs (dCas9-FP) after Tet-On induction in live cells and compared it with the time course of dCas9-FP expression in experimental dCas9-FP-expressing tumor xenografts using a combination of fluorescence imaging and in vivo contrast-assisted magnetic resonance imaging for assessing the extent of tumor perfusion. In vivo Dox-induction of mCherry-chimera expression occurred in tumor xenografts as early as 24 h post-induction and was visualized by using optical clearing (OC) of the skin. OC via topical application of gadobutrol enabled high-contrast imaging of FP expression in tumor xenografts due to a 1.1-1.2-fold increase in FI in both the red and green channels.

Optical Tissue Clearing Enables Three-Dimensional Morphometry in Experimental Nerve Regeneration Research.

Novel optical tissue clearing techniques enable three-dimensional imaging of entire organs at a subcellular resolution while preserving tissue architecture and fluorescence. In conjunction with computational image segmentation and automated analysis, these techniques provide fast and precise three-dimensional morphometry. Here, we present a tissue clearing protocol adapted to nerves and their motor and sensory targets in experimental rat models. Given their rapid processing times, low costs, and wide-ranging applicability, these techniques are likely to be a key technology for future nerve repair studies.

Optical Tissue Clearing to Study the Intra-Pulmonary Biodistribution of Intravenously Delivered Mesenchymal Stromal Cells and Their Interactions with Host Lung Cells.

Mesenchymal stromal cells (MSCs) injected intravenously are trapped in the capillaries of the lungs and die within the first 24 h. Studying the biodistribution and fate of labelled therapeutic cells in the 3D pulmonary context is important to understand their function in this organ and gain insights into their mechanisms of action. Optical tissue clearing enables volumetric cell tracking at single-cell resolution. Thus, we compared three optical tissue-clearing protocols (Clear, Unobstructed Brain/Body Imaging Cocktails and Computational analysis (CUBIC), modified stabilised 3D imaging of solvent-cleared organs (s-DISCO) and ethyl cinnamate (ECi)) to evaluate their potential to track the biodistribution of human umbilical cord MSCs expressing the tdTomato fluorescence reporter and investigate how they interact with host cells in the mouse lung. The results showed that although CUBIC clearing is the only method that enables direct imaging of fluorescently labelled MSCs, combining s-DISCO or ECi with immunofluorescence or dye labelling allows the interaction of MSCs with endothelial and immune cells to be studied. Overall, this comparative study offers guidance on selecting an optical tissue-clearing method for cell tracking applications.

Confocal Raman Micro-Spectroscopy for Discrimination of Glycerol Diffusivity in Ex Vivo Porcine Dura Mater.

Simple SummaryOptical clearing is a promising method to overcome limitations in optical imaging technology for in-depth investigation. In this paper, 50% glycerol diffusivity in the framework of a passive diffusion model and water migration in ex vivo porcine dura mater was studied using confocal Raman micro-spectroscopy. Results show that glycerol concentration and diffusion coefficient vary at different depths, and collagen-related Raman band intensities were significantly increased for all depths after treatment. In addition, the changes in water content during optical clearing showed that 50% glycerol induces dehydration. Furthermore, these results could be translated to other fibrous biological tissues and organs.Dura mater (DM) is a connective tissue with dense collagen, which is a protective membrane surrounding the human brain. The optical clearing (OC) method was used to make DM more transparent, thereby allowing to increase in-depth investigation by confocal Raman micro-spectroscopy and estimate the diffusivity of 50% glycerol and water migration. Glycerol concentration was obtained, and the diffusion coefficient was calculated, which ranged from 9.6 × 10−6 to 3.0 × 10−5 cm2/s. Collagen-related Raman band intensities were significantly increased for all depths from 50 to 200 µm after treatment. In addition, the changes in water content during OC showed that 50% glycerol induces tissue dehydration. Weakly and strongly bound water types were found to be most concentrated, playing a major role in the glycerol-induced water flux and OC. Results show that OC is an efficient method for controlling the DM optical properties, thereby enhancing the in-depth probing for laser therapy and diagnostics of the brain. DM is a comparable to various collagen-containing tissues and organs, such as sclera of eyes and skin dermis.

Rapid Optical Clearing for Semi-High-Throughput Analysis of Tumor Spheroids

Rapid Optical Clearing for Semi-High-Throughput Analysis of Tumor Spheroids

Rapid Optical Clearing for Semi-High-Throughput Analysis of Tumor Spheroids.

Tumor spheroids are fast becoming commonplace in basic cancer research and drug development. Obtaining data regarding protein expression within the spheroid at the cellular level is important for analysis, yet existing techniques are often expensive, laborious, use non-standard equipment, cause significant size distortion, or are limited to relatively small spheroids. This protocol presents a new method of mounting and clearing spheroids that address these issues while allowing for confocal analysis of the inner structure of spheroids. In contrast to existing approaches, this protocol provides for rapid mounting and clearing of a large number of spheroids using standard equipment and laboratory supplies. Mounting spheroids in a pH-neutral agarose-PBS gel solution before introducing a refractive-index-matched clearing solution minimizes size distortion common to other similar techniques. This allows for detailed quantitative and statistical analysis where the accuracy of size measurements is paramount. Furthermore, compared to liquid clearing solutions, the agarose gel technique keeps spheroids fixed in place, allowing for the collection of three-dimensional (3D) confocal images. The present article elaborates how the method yields high-quality two- and 3D images that provide information about inter-cell variability and inner spheroid structure.

The Effect of Different Optical Clearing Agents on the Attenuation Coefficient and Epidermal Thickness of Human Skin Assessed by Optical Coherence Tomography

Background: Optical coherence tomography (OCT) is a non-invasive imaging technique based on the interferometry of backscattered light. However, strong light scattering hinders its applicability in clinical dermatology. The strength of scattering is exemplified by the attenuation coefficient which is the rate of OCT signal decay in depth. Attenuation can be reduced by topical application of hyperosmotic liquids with a high refractive index, namely optical clearing agents (OCAs). In this study, we assessed the impact of different OCAs to enhance skin optical permeability in OCT images. In vivo tests were carried out to determine the OCT attenuation coefficient (μOCT) and epidermal thickness in the treated and untreated epidermis. Methods: Four OCAs were studied: Propylenglycol, propylenglycol combined with oleic acid in equal proportions (1:1 v/v), Vaseline, and liquid Vaseline. Percentage change of μOCT and epidermal thickness were estimated by OCT imaging of a healthy forearm skin, prior to the application of each OCA and after the application, at two time points, t1 = 5 min, and t2 = 90 min. μOCT was quantitatively obtained by fitting the OCT signal to a single scattering model. Results: The application of OCAs induced significant changes in both μOCT (decreased) and epidermal thickness (increased). The synergistic effect of the combined propylenglycol with oleic acid reduced the μOCT by 43% while propylenglycol induced the highest increase (33%) in epidermal thickness, both at t2. Conclusions: Topical administration of propylenglycol combined with oleic acid can reduce light attenuation in OCT imaging within the clinically relevant timeframe of 90 min.

Optical clearing and testing of lung tissue using inhalation aerosols: prospects for monitoring the action of viral infections.

Optical clearing of the lung tissue aims to make it more transparent to light by minimizing light scattering, thus allowing reconstruction of the three-dimensional structure of the tissue with a much better resolution. This is of great importance for monitoring of viral infection impact on the alveolar structure of the tissue and oxygen transport. Optical clearing agents (OCAs) can provide not only lesser light scattering of tissue components but also may influence the molecular transport function of the alveolar membrane. Air-filled lungs present significant challenges for optical imaging including optical coherence tomography (OCT), confocal and two-photon microscopy, and Raman spectroscopy, because of the large refractive-index mismatch between alveoli walls and the enclosed air-filled region. During OCT imaging, the light is strongly backscattered at each air–tissue interface, such that image reconstruction is typically limited to a single alveolus. At the same time, the filling of these cavities with an OCA, to which water (physiological solution) can also be attributed since its refractive index is much higher than that of air will lead to much better tissue optical transmittance. This review presents general principles and advances in the field of tissue optical clearing (TOC) technology, OCA delivery mechanisms in lung tissue, studies of the impact of microbial and viral infections on tissue response, and antimicrobial and antiviral photodynamic therapies using methylene blue (MB) and indocyanine green (ICG) dyes as photosensitizers.

Abstract 1876: ROCKETS Science: A novel processing toolbox for light sheet microscopy reveals unknown binding sites for EpCAM-targeted antibodies

Abstract Summary: We present a novel light sheet fluorescence microscopy (LSFM)-based imaging platform and corresponding set of procedures for greatly improved preclinical investigation of the biodistribution of novel drug candidates by the example of an EpCAM-targeting antibody. Methods: An anti-EpCAM antibody (G.8.8R) was applied intravenously to mice. Whole mice or individual organs were optically cleared following novel protocols, which we termed Rapid Optical Clearing Kit for Enhanced Tissue Scanning (ROCKETS). The procedures enabled processing of mouse organs and entire bodies for LSFM. For the GI tract, we developed 3D-Swiss rolls, a method that enables fixation, clearing and imaging of intestines in a compact form as a whole. The new procedures allowed us to investigate the biodistribution of G.8.8R in the entire mouse body and highly detailed in individual organs. Results: The ROCKETS concept achieved full transparency of any mouse organ, the entire GI tract and whole mouse bodies. All positive organs were easily identified in scans of whole mice, thereby providing excellent guidance for scanning of positive individual organs at higher magnifications. We detected G8.8R bound to all normal cuboidal and columnar epithelia, as well as in lymphoid organs and were able to reproducibly score binding levels. All reported EpCAM+ tissues in mice were accessed by G8.8R after intravenous application and binding was restricted to basolateral membranes of epithelia, as expected from published expression analyses. Moreover, we detected G8.8R in tissues that were reported EpCAM- or were not investigated, e.g. gustatory papillae of the tongue, choroid plexi in the brain or lingual mucous salivary glands. 3D-Swiss rolls of the GI tract revealed a highly heterogeneous binding pattern in the stomach, while the pattern along the small intestine was overall homogeneous. All binding was restricted to basolateral membranes of epithelial cells. We detected a general gradient of signals, decreasing from the bottom of the crypts to differentiated cells in all tissues, corresponding to described EpCAM downregulation with progressing differentiation. Furthermore, we first describe significantly increased signals at the common bile duct, major and minor duodenal papillae, as well as the mucosa in proximity of Peyer's patches (PP). Conclusions: The developed ROCKETS toolbox allowed for simple preparation of mouse organs and bodies for high-quality LSFM imaging. Our investigations of the highly heterogeneous biodistribution of G8.8R revealed previously unknown EpCAM binding locations, which may have far-reaching implications for EpCAM-targeting therapeutics in general, many of which failed in clinical studies due to dose limiting toxicities. In the future, the developed LSFM-imaging platform may contribute valuable data to preclinical drug development studies of any targeted therapeutic. Citation Format: Joerg P. Mueller, Nils O'Brien, Franz Osl, Frank Herting, Christian Klein, Pablo Umana, Sara Colombetti, Thomas Poeschinger, Andreas Beilhack. ROCKETS Science: A novel processing toolbox for light sheet microscopy reveals unknown binding sites for EpCAM-targeted antibodies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1876.

Immersion optical clearing of adipose tissue in rats: ex vivo and in vivo studies.

Optical clearing (OC) of adipose tissue has not been studied enough, although it can be promising in medical applications, including surgery and cosmetology, for example, to visualize blood vessels or increase the permeability of tissues to laser beams. The main objective of this work is to develop technology for OC of abdominal adipose tissue in vivo using hyperosmotic optical clearing agents (OCAs). The maximum OC effect (77%) was observed for ex vivo rat adipose tissue samples exposed to OCA on fructose basis for 90 minutes. For in vivo studies, the maximum effect of OC (65%) was observed when using OCA based on diatrizoic acid and dimethylsulfoxide for 120 minutes. Histological analysis showed that in vivo application of OCAs may induce a limited local necrosis of fat cells. The efficiency of OC correlated with local tissue damage through cell necrosis due to accompanied cell lipolysis.

Can 595-nm Pulsed Dye Laser in Conjunction With an Optical Clearing Agent Improve the Treatment of Port-Wine Stains?

Studies have demonstrated that glycerol can act as an optical clearing agent (OCA) to increase the light penetration through the skin and laser deposition to the target chromophore, thus potentially increasing the efficacy of laser treatment. To evaluate whether a pulsed dye laser (PDL) in combination with an OCA can increase the efficacy in treating port-wine stains (PWSs). Thirteen patients with untreated PWSs underwent 3 treatment sessions at 6-week intervals. Each PWS was divided into OCA + PDL sites (PDL treatment after topical use of 0.5 mL hydrous glycerol for 5 minutes), PDL sites, and untreated sites. The chromametric evaluation and visual evaluation (VAS) of the efficacy and the assessment of side effects were conducted 3 months after the final treatment. Visual evaluation was 2.69 versus 2.07 (p = .025) and 3.38 versus 3.07 (p = .04) for OCA + PDL and PDL-only sites after the first and second sessions. After the third session, the chromameter and VAS indicated no significant difference between the 2 sites. Permanent side effects were not observed. Greater efficacy was observed after the first 2 treatments on the OCA + PDL sites. Although after multiple sessions, the OCA + PDL treatment did not improve efficacy over just PDL alone.

Optical Clearing Agents for Optical Imaging Through Cartilage Tympanoplasties: A Preclinical Feasibility Study.

Optical clearing agents (OCAs) can render cartilage tympanoplasty grafts sufficiently transparent to permit visualization of middle ear structures in an operated ear using optical coherence tomography (OCT) imaging. Pieces of human tragal cartilage were treated with glycerol, a commonly used OCA. A reference reflector was imaged with OCT through the tympanoplasty as it cleared and the optical attenuation of the graft was measured. The reversibility of clearing and the dimensional changes associated with glycerol absorption were also measured. In a separate experiment, a human cadaveric temporal bone was prepared to simulate an ossiculoplasty surgery with cartilage replacement of the tympanic membrane. A partial ossicular replacement prosthesis (PORP) inserted in the ear was imaged with OCT through a 0.4mm cartilage graft optically cleared with glycerol. The optical attenuation of 0.4mm cartilage grafts decreased at 2.3+/-1.1 dB/min following treatment with glycerol, reaching a total decrease in attenuation of 13.6+/-5.9 dB after 7 minutes. The optical and dimensional effects of glycerol absorption were reversable following saline washout. In the temporal bone preparation, treatment of a cartilage graft with glycerol resulted in a 13 dB increase in signal-to-noise ratio and a 13 dB increase in contrast for visualizing the PORP through the graft with OCT. Optical clearing agents offer a potential pathway towards optical coherence tomography imaging of the middle ear in post-surgical ears with cartilage grafts.

MR and fluorescence imaging of gadobutrol-induced optical clearing of red fluorescent protein signal in an in vivo cancer model.

Multimodality registration of optical and MR images in the same tissue volume in vivo may be enabled by MR contrast agents with an optical clearing (OC) effect. The goals of this study were to (a) investigate the effects of clinical MR contrast agent gadobutrol (GB) and its combinations as a potential OC agent assisting in fluorescence intensity (FI) imaging in vivo and (b) evaluate MRI as a tool for imaging of topical or systemic application of GB for the purpose of OC. Subcutaneous tumor xenografts expressing red fluorescent marker protein were used as disease models. MRI was performed at 1 T 1 H MRI using T1 -weighted 3D gradient-echo (T1w-3D GRE) sequences to measure time-dependent MR signal intensity changes by region of interest analysis after image segmentation. Topical application of 1.0 M or 0.7 M GB-containing OC mixture with water and dimethyl sulfoxide showed similar 30-40% increases of tumor FI during the initial 15 min. Afterwards, the OC effect of GB on FI and tumor/background FI ratio showed a decrease over time in the case of 1.0 M GB, unlike the 0.7 M GB mixture, which resulted in a steady increase of FI and tumor/background ratio for 15-60 min. The use of T1w-3D GRE MR pulse sequences showed that concentrated 1.0 M GB resulted in MR signal loss of the skin due to high magnetic susceptibility and that signal loss coincided with the OC effect. Intravenous injection of 0.3 mmol GB/kg resulted in a rapid but transient 40% increase of FI of the tumors. Overall, 1 T MRI enabled tracking of GB-containing OC compositions on the skin surface and tumor tissue, supporting the observation of a time-dependent FI increase in vivo.

Optical Coherence Elastography as a Tool for Studying Deformations in Biomaterials: Spatially-Resolved Osmotic Strain Dynamics in Cartilaginous Samples.

This paper presents a recently developed variant of phase-resolved Optical Coherence Elastography (OCE) enabling non-contact visualization of transient local strains of various origins in biological tissues and other materials. In this work, we demonstrate the possibilities of this new technique for studying dynamics of osmotically-induced strains in cartilaginous tissue impregnated with optical clearing agents (OCA). For poroelastic water-containing biological tissues, application of non-isotonic OCAs, various contrast additives, as well as drug solutions administration, may excite transient spatially-inhomogeneous strain fields of high magnitude in the tissue bulk, initiating mechanical and structural alterations. The range of the strain reliably observed by OCE varied from ±10−3 to ±0.4 for diluted and pure glycerol, correspondingly. The OCE-technique used made it possible to reveal previously inaccessible details of the complex spatio-temporal evolution of alternating-sign osmotic strains at the initial stages of agent diffusion. Qualitatively different effects produced by particular hydrophilic OCAs, such as glycerol and iohexol, are discussed, as well as concentration-dependent differences. Overall, the work demonstrates the unique abilities of the new OCE-modality in providing a deeper insight in real-time kinetics of osmotically-induced strains relevant to a broad range of biomedical applications.

Optical Clearing of Plant Tissues for Fluorescence Imaging.

It is challenging to directly observe the internal structure of multi-layered and opaque plant specimens, without dissection, under a microscope. In addition, autofluorescence attributed to chlorophyll hampers the observation of fluorescent proteins in plants. For a long time, various clearing reagents have been used to make plants transparent. However, conventional clearing reagents diminish fluorescent signals; therefore, it has not been possible to observe the cellular and intracellular structures with fluorescent proteins. Reagents were developed that can clear plant tissues by removing chlorophyll while maintaining fluorescent protein stability. A detailed protocol is provided here for the optical clearing of plant tissues using clearing reagents, ClearSee (CS) or ClearSeeAlpha (CSA). The preparation of cleared plant tissues involves three steps: fixation, washing, and clearing. Fixation is a crucial step in maintaining the cellular structures and intracellular stability of fluorescent proteins. The incubation time for clearing depends on the tissue type and species. In Arabidopsis thaliana, the time required for clearing with CS was 4 days for leaves and roots, 7 days for seedlings, and 1 month for pistils. CS also required a relatively short time of 4 days to make the gametophytic leaves of Physcomitrium patens transparent. In contrast, pistils in tobacco and torenia produced brown pigment due to oxidation during CS treatment. CSA reduced the brown pigment by preventing oxidation and could make tobacco and torenia pistils transparent, although it took a relatively long time (1 or 2 months). CS and CSA were also compatible with staining using chemical dyes, such as DAPI (4',6-diamidino-2-phenylindole) and Hoechst 33342 for DNA and Calcofluor White, SR2200, and Direct Red 23 for the cell wall. This method can be useful for whole-plant imaging to reveal intact morphology, developmental processes, plant-microbe interactions, and nematode infections.

Optical Clearing of Plant Tissues for Fluorescence Imaging

It is challenging to directly observe the internal structure of multi-layered and opaque plant specimens, without dissection, under a microscope. In addition, autofluorescence attributed to chlorophyll hampers the observation of fluorescent proteins in plants. For a long time, various clearing reagents have been used to make plants transparent. However, conventional clearing reagents diminish fluorescent signals; therefore, it has not been possible to observe the cellular and intracellular structures with fluorescent proteins. Reagents were developed that can clear plant tissues by removing chlorophyll while maintaining fluorescent protein stability. A detailed protocol is provided here for the optical clearing of plant tissues using clearing reagents, ClearSee (CS) or ClearSeeAlpha (CSA). The preparation of cleared plant tissues involves three steps: fixation, washing, and clearing. Fixation is a crucial step in maintaining the cellular structures and intracellular stability of fluorescent proteins. The incubation time for clearing depends on the tissue type and species. In Arabidopsis thaliana, the time required for clearing with CS was 4 days for leaves and roots, 7 days for seedlings, and 1 month for pistils. CS also required a relatively short time of 4 days to make the gametophytic leaves of Physcomitrium patens transparent. In contrast, pistils in tobacco and torenia produced brown pigment due to oxidation during CS treatment. CSA reduced the brown pigment by preventing oxidation and could make tobacco and torenia pistils transparent, although it took a relatively long time (1 or 2 months). CS and CSA were also compatible with staining using chemical dyes, such as DAPI (4',6-diamidino-2-phenylindole) and Hoechst 33342 for DNA and Calcofluor White, SR2200, and Direct Red 23 for the cell wall. This method can be useful for whole-plant imaging to reveal intact morphology, developmental processes, plant-microbe interactions, and nematode infections.

3D Image Analysis for Nuclear Morphology in Osteocytic Spheroids with Optical Clearing Technique

3D Image Analysis for Nuclear Morphology in Osteocytic Spheroids with Optical Clearing Technique

Impact of optical clearing on ex vivo human skin optical properties characterized by spatially resolved multimodal spectroscopy.

A spatially resolved multimodal spectroscopic device was used on a two-layered "hybrid" model made of ex vivo skin and fluorescent gel to investigate the effect of skin optical clearing on the depth sensitivity of optical spectroscopy. Time kinetics of fluorescence and diffuse reflectance spectra were acquired in four experimental conditions: with optical clearing agent (OCA) 1 made of polyethylene glycol 400 (PEG-400), propylene glycol and sucrose; with OCA 2 made of PEG-400 and dimethyl sulfoxide (DMSO); with saline solution as control and a "dry" condition. An increase in the gel fluorescence back reflected intensity was measured after optical clearing. Effect of OCA 2 turned out to be stronger than that of OCA 1, possibly due to DMSO impact on the stratum corneum keratin conformation. Complementary experimental results showed increased light transmittance through the skin and confirmed that the improvement in the depth sensitivity of the multimodal spectroscopic approach is related not only to the dehydration and refractive indices matching due to optical clearing, but also to the mechanical compression of tissues caused by the application of the spectroscopic probe.