Strand displacement–triggered biocatalytic precipitation on ZIF-8/Bi2S3 photoelectrode: an aptasensing platform for sub-nanomolar kanamycin determination

Growing needs for monitoring kanamycin (KAN) residues in food require ultrasensitive, field-deployable determination platforms. Herein, we present a universal photoelectrochemical (PEC) aptasensing strategy that synergizes ZIF-8/Bi 2 S 3 heterostructure-engineered photoelectrodes with strand displacement–triggered biocatalytic signal amplification. The urchin-like ZIF-8/Bi 2 S 3 heterojunction, synthesized through in situ MOF growth on semiconductor nanoarchitectures, demonstrates exceptional photocurrent generation via facilitated carrier separation achieved by directional electron transfer from Bi 2 S 3 to ZIF-8 and hole scavenging by ascorbic acid. Capitalizing on aptamer-target recognition in homogeneous phase, KAN concentration is transduced into messenger DNA (S2) through displacement dynamics, overcoming steric limitations of conventional solid-phase biosensing. The liberated S2 hybridizes with electrode-immobilized S1 to assemble MnPP-loaded dsDNA, where the mimic enzyme catalyzes H 2 O 2 -driven precipitation of benzo-4-chlorohexadienone (4-CD). This biocatalytic insulation layer induces quantifiable photocurrent attenuation proportional to KAN levels (10–1.0 × 10 6  nmol/L), achieving a 0.1 nM detection limit superior to ELISA and HPLC. The platform demonstrates 95.7–105.4% recovery in milk matrices and cross-reactivity below 5.8% against structural analogs, validating its specificity. By integrating MOF-semiconductor interfacial engineering with homogeneous-to-heterogeneous signal translation, this work establishes a paradigm for antibiotic monitoring that bridges laboratory innovation with on-site applicability. Graphical abstract