Papain-capped gold nanoflowers: dual functionality as peroxidase mimic and 4-nitrophenol reduction catalysts

A bifunctional ensemble of papain-capped gold nanoparticles (AuNFs) exhibits dual functionality, manifesting peroxidaselike and 4-nitrophenol reduction activities. The AuNFs, possessing an average size of approximately 82.27 ± 1.95 nm, are synthesized under ambient conditions through the mediation of papain, wherein the reduction of HAuCl4 by ascorbic acid is facilitated. These nanoflowers are capable of catalyzing H₂O₂ to oxidize the target 3,3,5,5-tetramethylbenzidine, resulting in the production of a visual color of blue. Therefore, a simple method providing a sensitivity of 0.44 µM (signal/noise ratio = 2) and a linearity within the range of 0 to 40 µM is available to detect H₂O₂ by colorimetry. Subsequently, the chemical activity associated with the 4-NP (4-nitrophenol) reduction was studied, and it was found to exhibit a catalysis rate of 0.29 min^-1 , surpassing that of alternative gold catalysts. These findings underscore the potential utility of our AuNFs in catalytic and biosensing applications.