Optimization of the preparation of glass-coated, dye-tagged metal nanoparticles as SERS substrates

Dye-tagged metal nanoparticles are of significant interest in SERS-based sensitive detection applications. Coating these particles in glass results in an inert spectral tag that can be used in applications such as flow cytometry with significant multiplexing potential. Maximizing the SERS signal obtainable from these particles requires care in partitioning available nanoparticle surface area (binding sites) between the SERS dyes and the functionalized silanes necessary for anchoring the glass coating. In this article, we use the metal-mediated fluorescence quenching of SERS dyes to measure surface areas occupied by both dyes and silanes and thus examine SERS intensities as a function of both dye and silane loading. Notably, we find that increased surface occupation by silane increases the aggregative power of added dye but that decreasing the silane coverage allows a greater surface concentration of dye. Both effects increase the SERS intensity, but obtaining the optimum SERS intensity will require balancing aggregation against surface dye concentration.