Au nanoparticle‐catalyzed electron transfer from ammonia‐borane to Ru(NH₃)₆³⁺ for sensitive biosensing

Abstract

Metal nanoparticle (NP)‐catalyzed electron transfer (ET) from a reducing agent to a metal complex is useful for signal amplification in biosensors. For efficient ET, the metal complex must undergo rapid outer‐sphere reactions, be highly water‐soluble, and effectively penetrate bio/organic layers on metal NPs. Our study identifies Ru(NH₃)₆³⁺ as well‐suited for this purpose. Among reducing agents, ammonia‐borane (AB) enables rapid metal NP‐catalyzed ET, with Au, Pt, and Pd NPs displaying similar catalytic activities. The pseudo second‐order rate constant for 20‐nm Au NP‐catalyzed ET from AB to Ru(NH₃)₆³⁺ (1.4 × 10⁸ M⁻¹ s⁻¹) approaches the diffusion‐controlled rate constant. Despite immunoglobulin G and bovine serum albumin passively adsorbed on Au NPs, catalytic activity remains largely unaffected. Applying Au NP‐catalyzed ET to prostate‐specific antigen detection in human serum achieves a low detection limit of 10 pg/mL. These findings highlight the potential of Ru(NH₃)₆³⁺ and AB in designing biosensors based on rapid catalytic reaction.