CuO-ZnO heterojunction-engineered V-gCN nanosheets coupled with multi-footed DNAzyme walker for highly catalytic, ultrasensitive and label-free electrochemical aptamer ertapenem assay.

Ertapenem (ER), a clinically important carbapenem antibiotic, is increasingly recognized as a residue contaminant that may accelerate the dissemination of antimicrobial resistance through environmental and food-chain exposure. Here, we report a label-free electrochemical aptasensor for ultrasensitive ER detection by coupling a heterojunction-engineered catalytic interface with multivalent DNA nanomachine amplification. The sensing interface was constructed from gold nanoparticle (AuNP)-decorated CuO-ZnO heterojunctions grown on vanadium-doped graphitic carbon nitride (V-gCN) nanosheets. In this architecture, V-gCN provides a conductive and high-surface-area scaffold, CuO-ZnO heterojunctions promote interfacial charge transfer and electrocatalytic activity, and AuNPs facilitate probe immobilization and biocompatible signal transduction. Target recognition by the ER aptamer releases an initiator strand that triggers catalytic hairpin assembly (CHA) circuit, generating abundant multi-footed DNAzyme walkers. In the presence of Mg2+, the walkers cleave electrode-confined hairpin substrates and liberate G-quadruplex strands that subsequently complex with hemin to form electroactive G-quadruplex/hemin. The resulting H2O2-mediated catalytic reduction of hemin is further amplified by the AuNPs/CuO-ZnO/V-gCN interface. Under optimized conditions, the aptasensor achieved linear range of 0.1 to 100 ng mL-1 with 58.99 pg mL-1 detection limit. The sensor also showed high selectivity against interferents of penicillin (PEN), meropenem (MR), imipenem (IMI), and biapenem (BIA) and satisfactory performance in spiked milk samples with recovery rate from 97.3% to 108.4%, demonstrating its potential for the establishment of various robust aptamer-based electrochemical biosensor for sensitive antibiotic-residue analysis.