Spectral Fingerprinting of Individual Cells Visualized by Cavity-Reflection-Enhanced Light-Absorption Microscopy

Abstract

The absorption spectrum of light is known to be a “molecular fingerprint” that enables analysis of the molecular type and its amount. It would be useful to measure the absorption spectrum in single cell in order to investigate the cellular status. However, cells are too thin for their absorption spectrum to be measured. In this study, we developed an optical-cavity-enhanced absorption spectroscopic microscopy method for two-dimensional absorption imaging. The light absorption is enhanced by an optical cavity system, which allows the detection of the absorption spectrum with samples having an optical path length as small as 10 μm, at a subcellular spatial resolution. Principal component analysis of various types of cultured mammalian cells indicates absorption-based cellular diversity. Interestingly, this diversity is observed among not only different species but also identical cell types. Furthermore, this microscopy technique allows us to observe frozen sections of tissue samples without any staining and is capable of label-free biopsy. Thus, our microscopy method opens the door for imaging the absorption spectra of biological samples and thereby detecting the individuality of cells.

Cell structure imaging with bright and homogeneous nanometric light source

“…The CL is absorbed or scattered by the specimen on the luminescent thin film and detected by an optical microscope (Olympus, BXFM) and a photomultiplier tube (PMT, Hamamatsu Photonics K. K., H10721‐20). Because the image contrast arises from absorption or scattering of the CL light source by the nanostructure of the specimen , the biological specimens can be observed by the EXA microscope without any labeling process. The advantage of our technique is label‐free imaging with high spatial resolution, and our technique has a limitation of the imaging depth.…”

Cavity-Enhanced Spectroscopy in Condensed Phases: Recent Literature and Remaining Challenges

“…Another recent innovation is the work of Arai et al [24] who used a confocal mirror cavity to image absorption within thin slices of tissue samples and cells. The beam waist of the fundamental Gaussian mode of a mirror resonator can be quite small (micrometer size range), and rastering of the spot across a 2D surface can allow spatial mapping.…”

Dynamic nano-imaging of label-free living cells using electron beam excitation-assisted optical microscope

“…In the EXA microscope, the image contrast is given by the scattering or absorption of the CL by the microstructure in the biological specimen. Since the light absorption of cell differs depending on the cell type and cell structure 26 , the EXA microscope has potential to separate the microstructure in the cells by using refractive or absorption coefficient difference of each structure from spectroscopic imaging. The EXA microscope only observes at near the surface of thin film with high resolution.…”