Fourier transform multipixel spectroscopy for quantitative cytology

A Fourier transform multipixel spectroscopy system was set up and applied to fluorescence microscopy of single living cells. Continuous fluorescence spectra for all pixels of the cell image were recorded simultaneously by the system. Multiple frames of data were first acquired and stored as a set of interferograms for each pixel of the image; they were then Fourier transformed and used as a spatially organized set of fluorescence spectra. Practical spectral resolution of 5 nm was achieved, typically, for 10⁴ pixels in a single cell. The net result was I ( x y ,λ), the fluorescence intensity ( I ) for each pixel of the image ( x y ), as function of wavelength (λ). The present study demonstrates that multipixel spectroscopy can reveal dynamic processes of the food-digestive cycle in the unicellular Paramecium vulgaris fed with algae. Spectral variability of fluorescence intensity at different cytoplasmic sites pinpointed the location of cellular deposits of chlorophyll (630 nm) and of pheophytin (695 nm), a digestive product of the chlorophyll. Localization of compartmental spectral changes was achieved using a 'similarity mapping' algorithm, followed by enhanced image construction. Similarity mapping based on the fluorescence spectrum of native chlorophyll revealed a highlighted image of the cell cytopharynx structure where algae were ingested. Phagolysosomes, migrating vacuoles and the cytoproct, each containing different ratios of pheophytin, were similarly imaged.