Gold nanoclusters and nanoparticles Enhanced Raman scattering properties

Abstract

We investigated the nanoparticle surface and morphology effects on SERS. We demonstrated that the nature of the surface structure and morphology of the gold nanoparticles strongly influence the Raman signal of a Raman probe. Drastic drop in Raman signal due to the disappearance of sharp edges and tips of the particles directly proved that such sharp structures can enhance the Raman signal to a large extent which is popularly known as  lightening rod effect . In addition to the individual size and geometry effects, assembled nanosystems can produce extremely large Raman signal enhancements. This effect has been employed for the detection of low concentration analytes placed among assembled nanoparticles. We used sulfur containing amino acid cysteine for linear and controlled assembly of gold nanoparticles of different shapes. Raman enhancement factor was maximal for multi-spiked gold nanoparticles followed by gold nanorod and nanospheres. Finally, we studied the enhanced chemical effects in terms of catalytic activities of gold nanoclusters and nanoparticles. We compared the catalytic effects of the gold nanosystem sizes/concentrations on the reduction reaction of o nitro aniline to 1,2 benzenediamine. Rate constant value decreased as the size of gold nanocluster increased from lt1 nm to ~7.5 nm. Smaller gold nanosystems acted as better catalysts for the reduction reaction compared to the larger ones. This demonstrates that free-standing gold nanoclusters can act as better catalysts than the nanoparticles.