A new dimension for cell identification by FTIR spectroscopy: depth profiling in attenuated total reflection.

The multiresistant phenotype is an important problem in cancer chemotherapy. It is characterized by cell resistance to multiple and structurally unrelated drugs. We have shown previously that K562 multiresistant leukemia cells could be differentiated from their sensitive counterparts (wild-type K562 cells) on the basis of their infrared spectrum. In ATR FTIR mode, the penetration depth is controlled by both the wavelength and the incident angle, allowing depth profiling of samples. In this paper we took advantage of the ATR capability to modulate the penetration depth of the infrared wave into the cell, by modulating the incident angle, to investigate the differences between K562 multiresistant cells and their sensitive counterparts (wild-type K562 cells) as a function of this penetration depth. It is shown that focusing the IR beam on the most discriminant depth allows improvement of the discrimination between multiresistant and sensitive K562 cells. It is suggested that the depth profile of the difference spectra could allow a more precise localization of the biochemical modifications arising within the multidrug resistance phenotype.