Generated Mercury(I) as a Peroxidase-like Activity Modulator via Stimulating the Expression of Active Sites of Silver Nanoparticles for Environmental Hg²⁺ Detection

Developing a peroxidase-like activity modulator to accurately regulate peroxidase-like activity has always been the primary challenge to be addressed. External stimulation can effectively modulate the electronic structure of metal-centered active sites, which optimizes the chemical reaction path and changes the peroxidase-like activity. Herein, in a weak acidic environment (pH = 6.0), we found that the electron transfer may occur between silver nanoparticles (Ag NPs) anchored on the surface of reduced graphene oxide/poly(ethylene glycol) (rGO/PEG) nanosheets and added mercury(II) (Hg2+), which can induce the formation of mercurous ions (Hg(I), Hg22+). Hg(I) with regulatory catalytic performance can stimulate the expression of the active sites of Ag NPs via optimizing the electronic structure so that the adsorbed H2O2 molecules can efficiently produce reactive oxygen intermediates (•OH and •O2–) and be stabilized on the surface of Ag NPs. Meanwhile, density functional theory (DFT) calculations showed that the generated Hg(I) significantly reduced the Gibbs free energy of the chemical reaction and provided a pathway for electron transfer, which effectively enhanced the peroxidase-like activity. Based on this finding, a visual colorimetric sensor was constructed to detect Hg2+ with a detection limit of 19.7 nM in the range of 0.02–5.0 μM. Finally, we confirmed that the developed rGO/PEG/Ag nanohybrids can quantitatively detect Hg2+ in the environment. This method is reliable and has potential advantages in the environmental application field.