2019 conference paper
Resonance Raman techniques for complex biological systems
Ultrafast Nonlinear Imaging and Spectroscopy VII, 11122, 111220N.
Resonance Raman offers a significant increase in Raman signal levels. We show how this can be used to select a specific molecule within a complex biosystem to study, in our case to determine if hemoglobin survives in ancient fossils. Key to this ability is the fact that the vibration must be on the same molecule as the absorption. Further, we show that the Raman fingerprint, or changes to it, can provide further selectivity or identify changes in that molecule based upon the particular sample. In our case, we find that the iron in the hemoglobin has oxidized into FeOOH, but still attached to both its porphyrin-like heme group and the protein network that gives the hemoglobin absorption. Very narrow Raman resonances are found in molecules with symmetry-forbidden, phonon-allowed absorptions. We show several in biologically relevant materials including that methylated-DNA (m-DNA) can be distinguished from non-methylated (n-DNA) with nano-bowtie- and resonance-enhanced Raman spectra. These efiects are retained when plasmon resonances are used to enhance a local region of the sample, but find that the overall signal from a uniformly distributed specimen is not increased significantly by the enhancement of a small region, so is not recommended unless the sample can be concentrated into that region.