FT-IR spectroscopic investigations of single cells on the subcellular level

Spatially resolved Fourier transform infrared (FT-IR) spectroscopy of single oral mucosa cells and FT-IR spectroscopy of liver cell fractions produced by sucrose density gradient centrifugation have been applied to acquire structural information of cell organelles. For the spatially resolved measurements, mapping as well as mercury cadmium telluride (MCT) focal plane array (FPA) detector techniques were utilized. Surprisingly, infrared spectra of distinct subcellular structures differed only slightly. Aside from a minor intensity increase of the symmetric and the antisymmetric PO2 bands in the spectra of the nucleus, all normalized infrared spectra exhibited a remarkably high degree of similarity. Considering the fact that more than 98% of the DNA and significant amounts of the RNA are concentrated in the nucleus which occupies in oral mucosa cells only 5% of the total cell volume, these findings may be interpreted as a proof of the hypothesis that DNA is partially ‘‘invisible’’ in infrared spectroscopy. The finding of comparably small IR spectroscopic differences between cell organelles was confirmed by measurements on cell fractions specifically enriched by sucrose density gradient centrifugation. Besides variations of the non-specific overall protein:lipid ratio, the IR spectra of the distinct pellets exhibited only slightly differing absorbance values for the PO2 bands. As found for the nuclei by spatially resolved microspectrometry, IR spectra of the nuclear pellet displayed minor increased absorbances of the PO2 band at 1083 cm 1 when compared to spectra of the mitochondrial or microsomal pellets. # 2002 Elsevier Science B.V. All rights reserved.