Magnetic–enzymatic synergy driven photoelectrochemical aptasensor on a microfluidic chip for sub-pM kanamycin detection†

The escalating global concern over antibiotic contamination in food chains and aquatic ecosystems demands innovative solutions for rapid, on-site monitoring of residual drugs. This study presents an autonomous microfluidic photoelectrochemical (PEC) biosensing platform that synergizes magnetic purification, enzymatic amplification, and nanohybrid-enhanced signal transduction for field-deployable, ultrasensitive kanamycin (KAN) detection. The system integrates three functional layers: aptamer-functionalized magnetic beads (MBs) for selective KAN isolation, alkaline phosphatase (ALP)-catalyzed hydrolysis of L-ascorbic acid 2-phosphate (AAP) to generate electron-donating ascorbic acid (AA), and a TiO₂/Nb₂C/carbon nitride (CN) photoanode with a type-II heterojunction architecture for an amplified photocurrent response. This cascaded mechanism achieves a 0.00142 nM detection limit (S/N = 3). Crucially, the polydimethylsiloxane (PDMS)-based microfluidic chip automates critical workflows—including target–probe mixing, dsDNA displacement, MB separation, and ALP–Apt transfer through serpentine channels and pressure-driven flow control, eliminating manual intervention. A wireless PEC module coupled with smartphone-based signal processing enables real-time parameter optimization and data transmission via Bluetooth, removing reliance on external instrumentation. The modular design permits rapid adaptation to diverse targets through interchangeable aptamers, validated via spike-recovery tests in real samples. By unifying enzymatic catalysis, magnetic microfluidics, and nanomaterial-engineered photoelectrochemistry, this work establishes a paradigm for decentralized biosensing that bridges laboratory-grade sensitivity with point-of-need practicality, addressing critical gaps in antibiotic monitoring for food safety and environmental surveillance.