Generation of simplified protein Raman spectra using three-color picosecond coherent anti-stokes Raman spectroscopy

The well-known and prominent marker bands of aromatic amino acids in Raman spectra of protein and peptide films are revisited in the frequency and time domains using three-color picosecond coherent anti-Stokes Raman spectroscopy (CARS). We show here that control of the probe delay allows the narrow width/long lifetime states to be observed free not only from nonresonant background and fluorescence contamination but also free from the spectral congestion that arises from the complex background of spectrally broader (shorter lifetime) vibrational modes. The reasonable limits of detection obtained indicate that such CARS methods may be useful for quantitative analysis of protein composition.