Dithiocarbamate-Coated SERS Substrates: Sensitivity Gain by Partial Surface Passivation

The surface-enhanced Raman scattering (SERS) activity of nanoporous gold (NPG) can be boosted by controlled surface passivation. The SERS activities of unfunctionalized NPG were first optimized by etching substrates with NaI/I2 (triiodide) and using 2-mercaptopyridine (2-MP) as the probing analyte. Gains in analyte sensitivity were then achieved by passivating the superficial regions of the NPG substrates with dimethyldithiocarbamate (Me2DTC) while leaving the more recessed “hot spots” available for SERS detection. Partial surface passivation with DTCs increased the substrate sensitivity to chemisorptive analytes such as 2-MP by an order of magnitude, whereas surface saturation lowered the sensitivity by an order of magnitude. The partially passivated NPG films can also be functionalized with supramolecular receptors for chemoselective SERS. Installation of a DTC-anchored terpyridine enabled the detection of divalent metal ions at trace levels, as determined by the complexation-induced shift of a characteristic Raman peak of the metal ion receptor.