Fundamental properties of metal nanoparticle assemblies

Colloidal Au and Ag particles are extremely valuable in their diversity and are easily self-assembled in two-dimensional array on organosilane derivatized oxide covered surfaces. Ag colloidal particles are strongly enhancing for surface enhanced Raman spectroscopy (SERS) but lack a reproducibility in size and shape and have been shown to denature some proteins. Au colloidal particles can be reproducibly made from 5 to 60 nm in diameter with standard deviation of 1 nm in large scale and are protein friendly but lack the strong enhancement for SERS. The effect of colloidal Au particle aggregation and colloidal particle size on SERS spectra were probed by SERS filtration experiments. In this approach, SERS and optical spectra were recorded for trans-1,2-bis(4-pyridyl)-ethylene (BPE)-aggregated solutions of colloidal Au filtered through straight-channel membranes with successively smaller diameters. The chemical and mechanical stability of 12 nm-diameter Au colloid particles affixed to surface-confined, mercapto-(SH) and amine-...