Electrical classification of the concentration of bioconjugated metal colloids after surface adsorption and silver enhancement

A scheme for an electrical classification of the solution concentration of bioconjugated colloidal gold particles is presented. It is based on the immobilization of the particles in the gap of microstructured electrodes, followed by a metal enhancement step and electrical measurements. The surface density of particles depends on the solution concentrations, and the metal enhancement classifies this density by yielding conductive surfaces only for densities above a threshold. Size enhancement ratios of up to 10 were observed for 30 nm particles and could be controlled by the incubation time.