Surface Enhanced Raman Optical Activity on Biomolecules in Local Optical Fields of Silver Nanoparticles

Abstract

Raman optical activity (ROA) results in small differences in the Raman spectra of chiral molecules depending on whether left-or right circularly polarized light has been used. Due to its origin in higher order effects ROA is an extremely weak phenomenon, usually 3-5 orders of magnitude smaller than Raman scattering. Here we combine Raman optical activity (ROA) and surface enhanced Raman scattering (SERS) and report ROA experiments performed on biologically relevant molecules on silver nanoparticles, such as adenosine and cytosine. Our studies show that adsorption and local optical field gradients may modify the ROA signature of a molecule: In the vicinity of plasmonic silver nanoparticles, adenosine and cytosine show a strong SEROA effect exhibiting circular induced differences (CIDs) on the order of ∼10-2 compared to 10-4 - 10-3 typically observed in ROA. The increase in CID in SEROA and the overall enhanced Raman signal allows improved experimental parameters in SEROA compared to ROA, such as dramatically shorter data acquisition times, reduced excitation power, and lower concentration of the target molecule. Keywords: Raman, Chirality, Silver nanoparticles, Raman optical activity.