In this paper, three vibrational spectroscopy techniques (Photothermal AFM-IR, high definition FT-IR, and Confocal Raman) were applied for subcellular chemical imaging of cholesteryl esters in PC-3 prostate cancer cells. This sample was chosen as it has a well-defined structure and heterogeneous composition. For the first time, the three techniques were applied to study the same sample and systematically compared in terms of image quality, spectral pattern, and chemical information.
The results showed that while all three techniques are useful in chemical imaging of cholesterol derivatives in cancer cells, the AFM-IR study exhibited higher spectral heterogeneity and higher spatial resolution in chemical mapping. AFM-IR spectra showed IR bands characteristic of lipids and proteins coexisting in the measurement area, and relative intensities of the IR bands vary depending on the locations and suggests diverse composition of the PC-3 prostate cancer cell. The spatial resolution of chemical mapping by AFM-IR was also found to be significantly higher (a factor of ~10 improvement for this specific sample) than high-definition FT-IR and confocal Raman. Overall, this study confirms the AFM-IR method as a powerful tool in local chemical imaging of cells at the nanoscale level.