Raman spectrum of PCh (line a); typical Raman spectra collected from the cytoplasm of ATII cells (line b), A549 cells (line c), ATI cells (line d) and TT1 cells (line e). Spectra have been corrected for instrument response, EMSC normalized, baseline-corrected, wavenumber alignment, and vector normalized. Light microscope pictures indicate the region probed by each scan. Spectra are offset for clarity. Scale bar = 10 μm. Correlation coefficients between the PCh spectrum and ATII, A549, ATI, and TT1 cytoplasm spectra shown are R = 0.970, 0.889, 0.859, and 0.817, respectively.