Discrimination of human stem cells by photothermal microspectroscopy

Stem cells have great potential in clinical medicine. Sensitive methods for stem cell identification are a requirement for the development of medical interventions involving these cells. To date, a definitive stem cell marker has not been discovered. We are exploring the use of photothermal microspectroscopy (PTMS) for the purpose of stem cell characterisation and identification in human corneal epithelium. PTMS measures heat fluctuations associated with infrared radiation absorption. The technique is advantageous over existing Fourier transform infrared (FTIR) spectroscopy methods in having a spatial resolution which is not diffraction limited, thus allowing examination at a sub-cellular scale. PTMS measurements are unaffected by IR opacity of the sample, giving the method a further edge in comparison to FTIR spectroscopy. We show that PTMS spectra can be used for the characterisation of stem cells and differentiated cells in the human corneal stem cell model. We demonstrate for the first time that PTMS spectra derived from these cell types segregate into separate data clusters after principal component analysis. The predominant wavenumbers responsible for this separation appear to be associated with nucleic acid structure and function. PTMS offers great promise as a technique for stem cell identification in tissue samples where spatial resolution at the cellular scale or better is required.