Résumé
Synchrotron infrared light is an ideal source for infrared microspectroscopy due to its high brightness and broadband nature. These characteristics facilitate the collection of high signal-to-noise spectra through small apertures (spatial resolution ≅ λ/2) [1], Using the advantages of the synchrotron infrared source, we are able to chemically image biological samples that are too small to examine with a conventional globar source. At Beamline U10B at the National Synchrotron Light Source, Brookhaven National Laboratory, we have imaged many components of single living cells, such as lipids (2900-2800 cm−1), proteins (Amide I, 1700-1600 cm−1; Amide II, 1574-1525 cm−1), and nucleic acids (1200-1280 cm−1). We first demonstrated the potentiality of this technique by imaging single living mouse hybridoma B cells during the process of mitosis [2]. By imaging the lipid components, we observed a high concentration of lipids in the center of the dividing cell, in the region where the contractile ring responsible for the cleavage furrow is located. In the current work, we have examined changes in living cells during the process of apoptosis, i.e. programmed cell death. Apoptosis was induced by using an anti-Fas monoclonal antibody and a Fas-positive hybridoma B cell line, which allowed us to control the kinetics of the apoptosis. At different time points after the induction of apoptosis, cells were collected and deposited between ZnS windows. Cells were mapped using 3x3 μm redundant square apertures and a 3 μm step size. As apoptosis progresses, we observe dramatic changes in the frequency of the Amide I band and also the appearance of a new band near 1740 cm−1. The feature at 1740 cm−1 was originally observed during the process of cell necrosis [2] and likely arises due to protein oxidation which occurs as a cell dies.