Catalytic Reactions on the Surface of Ag Nanoparticles: A Photochemical Effect and/or Molecule Property?

Abstract

Using time-dependent surface-enhanced Raman scattering (TDSERS), we demonstrate the surface-catalyzed oxidation of 3-hydroxy anthranilic acid (HAA) to its azo derivatives. No external source either in the form of laser excitation or heat was required for the surface-catalyzed reaction, which clearly established that thermal energy alone was sufficient. But the possibility of enhanced reaction rate due to the surface plasmon resonance could not be ignored. To mimic in vivo conditions that prevail in healthy and unhealthy cells, SERS measurements were recorded under different environmental conditions. It is shown that the surface-catalyzed azo formation and its isomerization were strongly dependent on the external conditions, namely, temperature, pH, and environment. A plausible mechanism based on electron transfer to the adsorbed O2 is proposed for the trans–cis isomerization. This study can lead toward a new strategy of surface-catalyzed reactions not only for the synthesis of azo dyes but also to distinguish between the normal and abnormal cells.