Detection of hyaluronic acid on a functionalized surface enhanced raman scattering substrate

Hyaluronic acid (HA) is a high molecular weight glycosaminoglycan found in the extracellular matrix and joints in the body. Elevated levels in the serum are associated with liver disease so detection at concentrations in the microgram per liter range is useful for monitoring cirrhosis progression. Conventional methods can measure HA in this range but they take several days and require multiple preparation steps. Surface-enhanced Raman scattering (SERS) could be an alternative as it yields specific signatures stemming from molecular vibrations and has been shown to provide large enhancement factors. However, due to its intrinsic negative charge HA does not readily adsorb on metallic surfaces. To overcome this, a functionalized SERS substrate was developed to immobilize HA. A cysteamine self-assembling monolayer in the trans conformation allows the HA carboxyl group to attach to the ligand´s amine group. The SERS signal can be used to monitor the concentration of cysteamine trans conformers in order to optimize HA attachment. In addition, SERS analysis shows an increase in HA Raman band intensity when immobilized to the substrate as compared to free HA on the substrate. Correlations between HA concentration and Raman band intensity are also discussed.