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Fourier transform infrared spectra of a single cell in transflection geometry are seen to vary significantly with position on the cell, showing a distorted derivative-like lineshape in the region of the optically dense nucleus. A similar behaviour is observable in a model system of the protein albumin doped in a potassium bromide disk. It is demonstrated that the spectrum at any point is a weighted sum of the sample reflection and transmission and that the dominance of the reflection spectrum in optically dense regions can account for some of the spectral distortions previously attributed to dispersion artefacts. Rather than being an artefact, the reflection contribution is ever present in transflection spectra and it is further demonstrated that the reflection characteristics can be used for cellular mapping.
Bassan, P., Byrne, H., Lee, J., Bonnier, F., Clarke, C., Dumas, P., Gazi, E., Brown, M., Clarke, N., Gardiner, P.: Reflection contributions to the dispersion artefact in FTIR spectra of single biological cells. Analyst, 134, 1171-1175. 2009.