Mechanistic insights into graphene quantum dots-mediated regulation of single-atom nanozyme activity for homogeneous dual-mode detection of acetamiprid.

A homogeneous colorimetric/ratiometric fluorescence biosensor was developed for acetamiprid (Ace) detection based on graphene quantum dots (GQDs)-regulated Fe/Mn-N-C single-atom nanozyme (SAzyme) activity. Aptamer-functionalized SAzymes with high peroxidase-like activity were hybridized with complementary DNA-modified GQDs (CS/GQDs) emitting fluorescence at 450 nm. Without Ace, the hybridized CS/GQDs suppressed SAzyme activity, likely through proposed substrate-access blocking and hydroxyl-radical scavenging mechanisms, while retaining intrinsic fluorescence. Upon Ace addition, the CS/GQDs are released from the SAzyme, restoring SAzyme activity. The reactivated SAzyme then catalyzes oxidation of OPD by H2O2 to yellow DAP, which quenches GQDs fluorescence via inner filter effect and emits at 570 nm. This cascaded signal transduction enables robust visual colorimetric readout and ratiometric fluorescence (I570/I450). The detection limits are 10.37 ng/mL and 3.79 ng/mL, respectively. Spiked food sample recoveries ranged from 93.65% to 103.05%, comparable to LC-MS/MS. These findings demonstrate a reliable, sensitive, and straightforward platform for Ace residue monitoring.