Unveiling the role of ATP in amplification of intrinsic peroxidase-like activity of gold nanoparticles.

Peroxidase enzyme-like activity of gold nanoparticles (AuNPs) is currently being investigated for the potential application in the several realms of biomedicines. However, little is explored about the peroxidase activity of AuNPs decorated with different surface charges. It is well-documented that the catalytic activity and the interaction with mammalian cells are significantly different among AuNPs carrying different surface charges. We have recently reported that ATP enhances the peroxidase-like activity of AuNPs and iron oxide nanoparticles. However, a comprehensive and systematic study to reveal the role of surface charge on nanoparticles peroxidase-like activity has not been studied. In this work, we have shown that AuNPs coated with PEG (PEG AuNPs), citrate (citrate AuNPs) or CTAB (CTAB AuNPs) exhibit varying peroxidase-like activity and the boosting effect imparted by ATP was also different. We found that the peroxidase-like activity of PEG AuNPs and citrate AuNPs is dependent on hydroxyl radical formation, whereas CTAB AuNPs did not show any significant activity under the same experimental conditions. We also studied the boosting effect of ATP on the peroxidase-like activity of PEG and citrate AuNPs. Although the use of ATP resulted in enhanced peroxidase-like activity; however, contrary to the expectation, it did not facilitate the enhanced production of hydroxyl radical. In further studies, we found that the likely mechanism of boosting effect by ATP is the stabilization of oxidized TMB after peroxidase reaction. ATP imparts stabilization to the oxidized TMB produced due to PEG AuNPs, citrate AuNPs as well as HRP.