Uncovering strong π-metal interactions on Ag and Au nanosurfaces under ambient conditions via in-situ surface-enhanced Raman spectroscopy

The interactions between aromatic molecules and metal nanoparticles are ubiquitous in nanotechnology. Currently, π-metal interactions under ambient conditions are well appreciated for VIIIB but not for IB metals. Here, we demonstrate the direct probing of π-metal interactions under ambient conditions with molecular specificity using surface-enhanced Raman spectroscopy (SERS), which reveals that aromatic hydrocarbons adsorb strongly from solution onto the surfaces of Ag and Au nanoparticles, provided there is no surface oxidation. Theoretical modeling shows that this adsorption is driven by dispersive π-metal interactions and that the aromatic molecules co-adsorb alongside surface ligands that are present initially on the nanosurface. Finding direct evidence for this long-neglected interaction has significant implications for various applications. This is demonstrated with SERS sensing of an aromatic drug molecule whose structure would typically suggest it to be weakly adsorbing, and indeed it is not detected on conventional Ag colloids due to surface oxidation, but it is found to adsorb strongly onto Au particles.