Metal Nanozyme with Ester Hydrolysis Activity in the Presence of Ammonia‐Borane and Its Use in a Sensitive Immunosensor

Metal nanoparticle surfaces are used for peroxidase‐ and oxidase‐like nanozymes but not for esterase‐like nanozymes. It is challenging to obtain rapid catalytic hydrolysis on a metal surface and even more so without a catalytically labile substrate. Here, we report that metal nanoparticle surfaces rapidly catalyze non‐redox ester hydrolysis in the presence of redox H3N−BH3 (AB). Metal hydrides are readily generated on a Pt nanoparticle (PtNP) from AB, and as a result the PtNP becomes electron‐rich, which might assist nucleophilic attack of H2O on the carbonyl group of an ester. The nanozyme system based on PtNP, AB, and 4‐aminonaphthalene‐1‐yl acetate provides an electrochemical signal‐to‐background ratio much higher than natural enzymes, due to the rapid ester hydrolysis and redox cycling involving the hydrolysis product. The nanozyme system is applied in a sensitive electrochemical immunosensor for thyroid‐stimulating hormone detection. The calculated detection limit is approximately 0.3 pg mL−1, which indicates the high sensitivity of the immunosensor using the PtNP nanozyme. Metal nanoparticle surfaces rapidly catalyze non‐redox ester hydrolysis in the presence of redox H3N−BH3. Metal hydrides on a Pt nanoparticle might assist nucleophilic attack of H2O on the carbonyl group of an ester. The ester hydrolysis is applied in a sensitive electrochemical immunosensor for thyroid‐stimulating hormone detection.