Tuning the electrocatalytic activity of electrodeposited defect-rich Au-NPs in redox reactions with dopamine through their facet engineering

This study examines the mechanistic basis of the facet-specific response of electrodeposited (ED) defect-rich gold nanoparticles (Au-NPs) in redox interactions with dopamine (DA). During the investigations, it was revealed that simple cysteamine (CystAm) modification of ED defect-rich Au-NPs leads to thiol (Au–SH) bond formation preferentially on Au(100)- and Au(110)-like surface sites. These sites are more active in oxygen reduction reactions (ORR) and redox reactions with free dopamine (DA). Their partial passivation is accompanied by an increased relative contribution of Au(111)-like sites on the surface of defect-rich ED Au-NPs. Au(111)-like sites are relatively inert toward ORR and DA redox reactions but remain active toward quinone, the enzymatic oxidation product of DA. Reduction of electrochemical contribution of Au(100)- and Au(110)-like sites was essential to prevent their participation and electrochemical interference with biochemical DA oxidation catalyzed by the enzyme tyrosinase. The obtained insights enabled the development of a specific DA biosensor based on CystAm-modified defect-rich ED Au-NPs, the enzyme tyrosinase, and a natural chitosan film. Importantly no electrochemically induced interference arising from Au(110)- and Au(100)-like sites was observed. The resulting biosensor enabled the detection of DA in synthetic urine over an analytically relevant concentration range (1–30 µM), with recoveries of 102–117% and an error <10 %.