Multispectral Imaging Autofluorescence Microscopy for the Analysis of Lymph-Node Tissues

Multispectral imaging for characterizing autofluorescent tissues

Selective Plane Illumination Microscopy (SPIM) has become an emerging technology since its first application for 3D in-vivo imaging of the development of a living organism. An extensive number of works have been published, improving both the speed of acquisition and the resolution of the systems. Furthermore, multispectral imaging allows the effective separation of overlapping signals associated with different fluorophores from the spectrum over the whole field-of-view of the analyzed sample. To eliminate the need of using fluorescent dyes, this technique can also be applied to autofluorescence imaging. However, the effective separation of the overlapped spectra in autofluorescence imaging necessitates the use of mathematical tools. In this work, we explore the application of a method based on Principal Component Analysis (PCA) that enables tissue characterization upon spectral autofluorescence data without the use of fluorophores. Thus, enabling the separation of different tissue types in fixed and living samples with no need of staining techniques. Two procedures are described for acquiring spectral data, including a single excitation based method and a multi-excitation scanning approach. In both cases, we demonstrate the effective separation of various tissue types based on their unique autofluorescence spectra.

Pericellular Matrix Formation and Atomic Force Microscopy of Single Primary Human Chondrocytes Cultured in Alginate Microgels

One of the main components of articular cartilage is the chondrocyte's pericellular matrix (PCM), which is critical for regulating mechanotransduction, biochemical cues, and healthy cartilage development. Here, individual primary human chondrocytes (PHC) are encapsulated and cultured in 50 µm diameter alginate microgels using drop-based microfluidics. This unique culturing method enables PCM formation and manipulation of individual cells. Over ten days, matrix formation is observed using autofluorescence imaging, and the elastic moduli of isolated cells are measured using AFM. Matrix production and elastic modulus increase are observed for the chondrons cultured in microgels. Furthermore, the elastic modulus of cells grown in microgels increases ≈ten-fold over ten days, nearly reaching the elastic modulus of in vivo PCM. The AFM data is further analyzed using a Gaussian mixture model and shows that the population of PHCs grown in microgels exhibit two distinct populations with elastic moduli averaging 9.0 and 38.0 kPa. Overall, this work shows that microgels provide an excellent culture platform for the growth and isolation of PHCs, enabling PCM formation that is mechanically similar to native PCM. The microgel culture platform presented here has the potential to revolutionize cartilage regeneration procedures through the inclusion of in vitro developed PCM.

Autofluorescence of blood and its application in biomedical and clinical research

Autofluorescence of blood has been explored as a label free approach for detection of cell types, as well as for diagnosis and detection of infection, cancer, and other diseases. Although blood autofluorescence is used to indicate the presence of several physiological abnormalities with high sensitivity, it often lacks disease specificity due to use of a limited number of fluorophores in the detection of several abnormal conditions. In addition, the measurement of autofluorescence is sensitive to the type of sample, sample preparation, and spectroscopy method used for the measurement. Therefore, while current blood autofluorescence detection approaches may not be suitable for primary clinical diagnosis, it certainly has tremendous potential in developing methods for large scale screening that can identify high risk groups for further diagnosis using highly specific diagnostic tests. This review discusses the source of blood autofluorescence, the role of spectroscopy methods, and various applications that have used autofluorescence of blood, to explore the potential of blood autofluorescence in biomedical research and clinical applications.

Autofluorescence Spectroscopy for Monitoring Metabolism in Animal Cells and Tissues

Excitation of biological substrates with light at a suitable wavelength can give rise to a light emission in the ultraviolet (UV)-visible, near-infrared (IR) spectral range, called autofluorescence (AF). This is a widespread phenomenon, ascribable to the general presence of biomolecules acting as endogenous fluorophores (EFs) in the organisms of the whole life kingdom. In cytochemistry and histochemistry, AF is often an unwanted signal enhancing the background and affecting in particular the detection of low signals or rare positive labeling spots of exogenous markers. Conversely, AF is increasingly considered as a powerful diagnostic tool because of its role as an intrinsic biomarker directly dependent on the nature, amount, and microenvironment of the EFs, in a strict relationship with metabolic processes and structural organization of cells and tissues. As a consequence, AF carries multiple information that can be decrypted by a proper analysis of the overall emission signal, allowing the characterization and monitoring of cell metabolism in situ, in real time and in the absence of perturbation from exogenous markers. In the animal kingdom, AF studies at the cellular level take advantage of the essential presence of NAD(P)H and flavins, primarily acting as coenzymes at multiple steps of common metabolic pathways for energy production, reductive biosynthesis and antioxidant defense. Additional EFs such as vitamin A, porphyrins, lipofuscins, proteins, and neuromediators can be detected in different kinds of cells and bulk tissues, and can be exploited as photophysical biomarkers of specific normal or altered morphofunctional properties, from the retinoid storage in the liver to aging processes, metabolic disorders or cell transformation processes. The AF phenomenon involves all living system, and literature reports numerous investigations and diagnostic applications of AF, taking advantage of continuously developing self-assembled or commercial instrumentation and measuring procedures, making almost impossible to provide their comprehensive description. Therefore a brief summary of the history of AF observations and of the development of measuring systems is provided, along with a description of the most common EFs and their metabolic significance. From our direct experience, examples of AF imaging and microspectrofluorometric procedures performed under a single excitation in the near-UV range for cell and tissue metabolism studies are then reported.