Direct Silica Encapsulation of Self-Assembled-Monolayer-Based Surface-Enhanced Raman Scattering Labels with Complete Surface Coverage of Raman Reporters by Noncovalently Bound Silane Precursors

Silica-coated surface-enhanced Raman scattering (SERS) labels with a self-assembled monolayer (SAM) on the entire surface of the metal colloid combine high chemical and mechanical stability with bright and reproducible Raman signals due to the complete surface coverage and uniform molecular orientation within the SAM. Currently available chemical syntheses are either based on the direct encapsulation of covalently bound silane precursors or comprise several steps, such as the sequential addition of noncovalently bound polyelectrolytes to render the surface vitreophilic. Here, a generic approach for the direct and fast silica encapsulation of commercially available Raman reporter molecules with polar head groups by noncovalently bound silane precursors is reported. The formation of highly SERS-active silica-coated clusters during silica encapsulation is determined by several parameters, in particular the type of Raman reporter molecule, the solvent, and the type and amount of the silane precursor.