A quadruple wavelength IR sensor system for label-free tumour screening

In this contribution, we present a novel quadruple wavelength infrared sensor system for measuring the CH₂-symmetric/CH₂-antisymmetric stretch ratio of biological cells. This ratio can be used as a marker to distinguish between healthy and carcinoma cells. Compared to common techniques our system does not require specific labelling or staining, or the use of expensive liquid nitrogen cooled IR spectrometers. Two of the four wavelengths, 3.33 and 3.57 µm, are used as reference points and the other two represent CH₂-symmetric and CH₂-antisymmetric stretch absorption (respectively at 3.51 and 3.42 µm). IR absorbance spectra recordings of healthy (MDCK) and malignant (Caki-1) epithelial kidney cells with a conventional IR spectroscope showed significant differences in the absorbance ratio 3.51 µm/3.42 µm (CH₂-symmetric/CH₂-antisymmetric stretch). The sensor has been validated by measuring the CH₂ stretch ratio of yeast samples both by IR spectroscopy and the sensor system. The methods yielded similar results. The application potential of our system is demonstrated by CH₂ stretch measurements on healthy and carcinoma epithelial kidney cells. Measurements on both cell types yielded significant differences in CH₂ stretch ratio. The sensor has the potential to be further developed into a fast, low-cost and label-free screening system for suspicious biopsy samples.