A AuNPs modified Cu-g-C3N4 nanozyme: Improved peroxidase-like activity for amaranth dual-mode fluorescence-SERS sensors

Abstract

In numerous studies, the stability of gold nanoparticles (AuNPs) has been predominantly centered on the selection of reducing agents. Thus, a comprehensive understanding of the catalytic stability of AuNPs is of critical importance for their practical applications. Herein, a composite nanozyme (Cu-g-C3N4/AuNPs) consisting of copper-doped graphitic carbon nitride (Cu-g-C3N4) and AuNPs was synthesized via a facile self-assembly approach. Within this system, Cu-g-C3N4 serves as both a stabilizer and an adsorbent for AuNPs. The results demonstrate that the as-prepared Cu-g-C3N4/AuNPs nanozyme exhibits superior peroxidase- (POD-) like activity and exceptional stability compared to the Cu-doped carbon dots/AuNPs (Cu-CDs/AuNPs) system. In the presence of H2O2, Cu-g-C3N4/AuNPs can efficiently catalyze the oxidation of amaranth (AT) to yield highly fluorescent oxidation products (ox-AT), accompanied by distinct alterations in surface-enhanced Raman scattering (SERS) signals. Based on this dual-signal response characteristic, a dual-mode fluorescence-SERS (FL-SERS) sensor for the detection of AT was developed. Characterization and comprehensive experimental results confirm that Cu-g-C3N4 facilitates more reactive oxygen species (ROS) generation than Cu-CDs/AuNPs, thereby endowing the nanozyme with higher catalytic activity. Stability tests indicate that, in contrast to Cu-CDs/AuNPs not assembled with g-C3N4, the Cu-g-C3N4/AuNPs nanozyme retains its activity for at least 7 days, with its long-term stability potentially extendable further.