Abstract
Micro-absorption spectroscopy provides a label-free nondestructive probe of biomolecules and their interaction at the single cell level. Our setup employs a confocal detection system to probe and spectrally resolve the attenuation of a white light beam in the axial direction. The method can be used to study cells in their native environment with a spatial resolution of two micron. We present measurements in the UV spectral range (220 - 350 nm) where aromatic amino acids and bases in nucleic acid absorb. To establish the accuracy of the method, we have measured the concentration dependence of the optical absorption of tryptophan, phenylalanine and DNA bases in a microcapillary with 50 micron pathlength and a volume of a few hundred nanoliters. The absorption in the micro setup is found to vary linearly with concentration. We explore applications to protein and DNA solution in nanoliter quantities and single cells.
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