Detection of potential osteoarthritis biomarkers using surface enhanced Raman spectroscopy in the near-infrared

A novel application of surface-enhanced Raman spectroscopy (SERS) for in-vitro osteoarthritis (OA) biomarker detection is described. Hyaluronic acid (HA) is a potential OA biomarker and synovial fluid levels of HA have been correlated with progression of joint space narrowing. However, current immunoassay and chromatographic methods that identify HA in synovial fluid are cumbersome and often require sophisticated instrumentation. Raman spectroscopy may be an alternative to these analytical methods, providing rapid identification of HA using characteristic Raman bands. Yet, previous reports of un-enhanced Raman spectroscopy for hyaluronic acid are in aqueous solutions exceeding 1000X in-vivo concentrations because HA is a weakly scattering polysaccharide. Surface-enhanced Raman spectroscopy can improve detection limits by 100-1000 times and we present, to our best knowledge, the first surface-enhanced Raman spectra of hyaluronic acid. Moreover, the recent commercial availability of stable SERS gold substrates has enabled rapid SERS detection of this biomarker at concentrations diluted by more than an order of magnitude, compared to previous literature reports. Preliminary results of easily and rapidly observing hyaluronic acid at low concentrations in aqueous solutions supported further studies in synthetic models of biofluids, such as artificial synovial fluid, that contain HA at low concentrations. These complex fluids contain proteins that compete for the SERS-active sites on the substrate, and the resulting spectra are dominated by protein Raman bands. We apply a simple and validated protein precipitation protocol to artificial synovial fluid prior to deposition onto the SERS substrate. We find that HA is easily detected in these fluids after protein removal treatment.