Discrimination of human stem cells by photothermal microspectroscopy

Abstract

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 subcellular 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.

Vibrational spectroscopic mapping and imaging of tissues and cells

“…Such a technique could ultimately lead to spatial resolutions of 20-30 nm, and the measurements are unaffected by IR opacity of the sample, which can be an important issue for other FTIR microscopies. The technique has now been applied to a variety of important biological problems, such as discrimination of human stem cells (Grude et al 2007(Grude et al , 2009), monitoring of cell cycles (Hammiche et al 2005) and the differentiation of exfoliative cervical cytology ).…”

Mid-infrared spectroscopy beyond the diffraction limit via direct measurement of the photothermal effect

“…The atomic force microscope (AFM) 7 is a widely used characterization platform because in addition to providing high resolution images of the sample topography, advanced AFM techniques can also provide local mechanical, 8 electrical, 9 thermal, [10][11][12] etc. 15 PTMS has been applied to characterize polymers, 15,16 stem cells, 17 and cervical cancer cells. For example, scanning thermal microscopy (SThM) 10,11,13,14 relies on probe tips with either a thermocouple or an electrically resistive element to obtain high resolution maps of the sample's thermal conductivity.…”

“…The photo-thermal signal is measured using a Wheatstone bridge (where the probe makes up one leg of the resistor bridge) and Fourier transformed to yield IR spectra with wavelength-independent resolution. 15 PTMS has been applied to characterize polymers, 15,16 stem cells, 17 and cervical cancer cells. 18 However, to the best of our knowledge no chemical maps have been reported using this method.…”

Syrian hamster embryo (SHE) assay (pH 6.7) coupled with infrared spectroscopy and chemometrics towards toxicological assessment

“…2,3 Recent applications of IR spectroscopy include characterization of cell cycle events, 4 disease progression, 5 adenocarcinoma, 6 cancer type, 7,8 and stem cells. [9][10][11][12][13][14][15] Although the great majority of studies are preliminary or investigative, efforts are concentrated towards rendering spectroscopy a reliable technique in screening and diagnosis. 8,16 The application of chemometric tools plays a major role in extracting information from IR-spectroscopy datasets.…”