Silver Nanocubes as Electrochemical Labels for Bioassays

Here, we report on the use of 40 ± 4 nm silver nanocubes (AgNCs) as electrochemical labels in bioassays. The model metalloimmunoassay combines galvanic exchange (GE) and anodic stripping voltammetry (ASV). The results show that a lower limit of detection is achieved by simply changing the shape of the Ag label yielding improved GE with AgNCs when compared to GE with spherical silver nanoparticles (sAgNPs). Specifically, during GE between electrogenerated Au³⁺ and the Ag labels, a thin shell of Au forms on the surface of the NP. This shell is more porous when GE proceeds on AgNCs compared to sAgNPs, and therefore, more exchange occurs when using AgNCs. ASV results show that the Ag collection efficiency (AgCE%) is increased by up to ∼57% when using AgNCs. When the electrochemical system is fully optimized, the limit of detection is 0.1 pM AgNCs, which is an order of magnitude lower than that of sAgNP labels.