Abstract

Biomolecules display specific vibrational signatures in the infrared (IR) range, and organelles that concentrate these biomolecules can be identified by these IR signatures. Subcellular identification and location of cell organelles using IR signatures is attractive as it does not require the use of any specific trackers and is thus non-invasive and non-destructive. We show here that endogenous IR absorptions are relevant to detecting and imaging the nucleus, the cytoplasm, and the Golgi apparatus/endoplasmic reticulum in MCF-7 breast cancer cells, and we compare these results with our previous work on the HeLa cell line. We correlate maps of fixed and dried cells obtained by synchrotron radiation Fourier transform infrared (SR FT-IR) spectromicroscopy with epifluorescence images using fluorescent trackers for Golgi apparatus and nucleus, namely BODIPY TR C<sub>5</sub>-ceramide complexed to BSA and DAPI, respectively. Interestingly, the ratios of the IR bands CH<sub>2</sub> : CH<sub>3</sub> (both asymmetric and symmetric) and CO<sup>(ester)</sup>:amide I were shown to be reliable gauges of the lipidic character of a cellular compartment, the -CH<sub>2</sub> and the CO<sup>(ester)</sup> absorptions increasing with the presence of inner membranes like in the Golgi apparatus.

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