Optical photothermal infrared (O-PTIR) micro-spectroscopic characterisation of breast cancer cell lines: a comparative molecular profile of MCF7, MDA-MB-231, and SKBR3 cells.

Understanding the biochemical diversity among breast cancer subtypes is essential for developing more precise diagnostic and treatment strategies. In this study, we use optical photothermal infrared (O-PTIR) micro-spectroscopy to characterise three human breast cancer cell lines-MCF7, MDA-MB-231, and SKBR3-without the need for dyes or labels. Unlike conventional FTIR, which is limited by a spatial resolution of ∼5 µm due to the IR wavelength dependent diffraction limits, O-PTIR achieves sub-micron resolution, allowing biochemical analysis at near-single organelle levels. By analysing the spectral data, we identified variations in key biomolecules such as nucleic acids, proteins, and lipids that correlate with the distinct biological characteristics of each cell type. Our approach also included peak deconvolution and ratiometric analysis, which provided further insight into the biochemical variations. Principal component analysis (PCA) was used to assess these differences and when coupled with and linear discriminant analysis (LDA) showed clear separation between the cell lines. These results highlight the potential of O-PTIR as a powerful tool for label-free cancer cell characterisation, overcoming FTIR limitations by using a pulsed mid-IR laser for absorption and a visible probe laser for detection, enabling reflection-mode detection that bypasses water interference and achieves submicron resolution.