The adsorption of ligands on the surfaces of colloidal Ag nanocubes was studied using <i>in-situ</i> surface enhanced Raman spectroscopy (SERS). In a typical experiment, time-resolved solution-phase SERS data were collected from a sample of Ag nanocubes dispersed in an ethanol-based ligand solution at different concentrations, from which we could evaluate the binding of the ligand to the Ag nanocubes. We found that 4-nitrothiophenol (4-NTP) would rapidly bind to the Ag surface due to the favorable thiol-Ag interactions. The red-shift of SERS peaks at lower concentrations suggests a different molecular orientation, consistent to what is described in the self-assembled monolayer (SAM) theory. We also found that 4-aminothiophenol (4-ATP) would also rapidly bind to Ag, but with significantly weaker SERS intensity due to the electron-donating amine group of 4-ATP. In addition, we evaluated the binding of 1,4-phenylene diisocyanide (1,4-PDI), which interacts with Ag weaker that thiols, and found that they would readily bind to the Ag nanocube surface. As the concentration of 1,4-PDI increased, we found that more molecules were oriented perpendicular to the surface. Finally, we evaluated the competitive adsorption of the thiol and isocyanide groups to Ag by introducing them simultaneously to Ag nanocubes. The signals for 1,4-PDI were not visible when the same amount of 4-NTP (4-ATP) as the 1,4-PDI was introduced simultaneously, and they were weakly visible only when their amount was increased relatively by 100 times. This suggests that thiols selectively bind to the Ag surface over isocyanides, inhibiting the adsorption of isocyanides to the Ag surface.

Evaluating the binding of ligands on silver nanocubes by <i>in situ</i> surface-enhanced Raman spectroscopy

2019 Fall National Meeting

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Evaluating the binding of ligands on silver nanocubes by in situ surface-enhanced Raman spectroscopy