Resonance Raman simplifies complex material study, from Hb in dinosaur fossils to one wavenumber wide enhancement in liquids

Complex materials inherently have complex spectroscopic signatures. This limits the ability to fully utilize powerful vibrational spectroscopy techniques such as Raman or infrared in these systems. Yet living systems, fossils, and many modern materials are complex systems, so a solution is needed. We present resonance Raman results in three systems to illustrate its ability to both identify the presence of a moiety, and if present, to use its resonantly enhanced Raman spectra to identify molecular modifications as usual in simpler systems. We find that the Raman enhancement is often large enough to make the Raman signal dominated by the molecules that contain the electronic absorption used to produce resonance. Comparison of on-resonance to a nearby off-resonance spectra substantiates this. The technique has been used to show that heme still attached to globin remnants still exists in soft tissue extracted from B. canadensis and T. rex, but that the heme outer ring has been damaged over time. Further, evidence of goethite growth on the Fe of the heme still attached to the globin remnants suggests possible preservation modes. Modern analogs show similar trends. In another study, we showed that methylated cytosine can be distinguished from un-methylated cytosine using resonance Raman and its sensitivity is state-of-the-art. Finally, a new class of resonant Raman on benzene produces Raman signal gain of 3500x with an excitation wavelength change of 0.01 nm. Such a combination of signal gain and narrow linewidth represents a further step in separation of chemical moieties in complex materials without sacrificing signal level (in fact increasing it w/o interferents) and still providing the information contained in the vibrational system.