Optical Photothermal Infrared Microspectroscopy Discriminates for the First Time Different Types of Lung Cells on Histopathology Glass Slides

The debate of whether a glass substrate can be used in Fourier transform infrared spectroscopy is strongly linked to its potential clinical application. Histopathology glass slides of 1 mm thickness absorb the mid-IR spectrum in the rich fingerprint spectral region. Thus, it is important to assess whether emerging IR techniques can be employed to study biological samples placed on glass substrates. For this purpose, we used optical photothermal infrared (O-PTIR) spectroscopy to study for the first time malignant and non-malignant lung cells with the purpose of identifying IR spectral differences between these cells placed on standard pathology glass slides. The data in this feasibility study showed that O-PTIR can be used to obtain good-quality IR spectra from cells from both the lipid region (3000–2700 cm–1) and the fingerprint region between 1770 and 950 cm–1 but with glass contributions from 1350 to 950 cm–1. A new single-unit dual-range (C–H/FP) quantum cascade laser (QCL) IR pump source was applied for the first time, delivering a clear synergistic benefit to the classification results. Furthermore, O-PTIR is able to distinguish between lung cancer cells and non-malignant lung cells both in the lipid and fingerprint regions. However, when these two spectral ranges are combined, classification accuracies are enhanced with Random Forest modeling classification accuracy results ranging from 96 to 99% across all three studied cell lines. The methodology described here for the first time with a single-unit dual-range QCL for O-PTIR on glass is another step toward its clinical application in pathology.