A stable surface-enhanced Raman scattering (SERS) substrate is developed through immobilization of gold sols onto aminated silica beads. The plasmon resonance is established by spacing of gold sols on the bead surface and remains stable over extended periods of time due to the large number of amine groups that provide stable anchoring of gold to the surface. Unlike planar supports, this substrate can be dispersed in a sample, providing high surface area for detection and efficient transport of analytes to its surface. This substrate can be used to detect the binding of a molecule to ligands on the silica surface, which avoids the stability limitations of thiol-bound ligands on gold. Chemical modification of the amine groups on the silica surface with benzoic anhydride could be readily detected in Raman scattering enhanced by the neighboring gold sols, with nearly the same sensitivity as benzylthiol bound directly to the gold surfaces. This result suggests future work involving the immobilization of other ligands through the residual amine groups to the silica, which could be used to selectively attract target analytes to the SERS-active surface.

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