Field-Deployable Photoelectrochemical Biosensor Using Atomically Defect-Engineered Heterojunction for Ultrasensitive Microcystin-LR Monitoring via Aptamer-Mediated Fe-S Conduction.

Effective monitoring of microcystin (MC)-LR toxin produced by blue-green algae is of great importance for water pollution and human health. Herein, a field-deployable (FiDe) photoelectrochemical (PEC) biosensor based on nitrogen vacancy-engineered Fe2O3@g-C3N4-6Nv was proposed for the sensitive and reliable detection of MC-LR. A critical insight was elucidated on atomic-level altered Fe-O/N coordination for an oriented built-in electric field in the composite, which thereby established a Z-scheme charge transfer for enhanced PEC responses. A thiolated aptamer, stably immobilized via Fe-S bonding, enabled specific MC-LR recognition with exceptional resilience. Synergistic integration of a defect-tailored Fe-N heterojunction and Fe-S aptamer immobilization precisely controlled interfacial charge dynamics through concentration-dependent target recognition, where MC-LR binding inhibited Fe-S/Fe-N electron transport to weaken PEC signals. Coupled with an in-house developed FiDe PEC device, the platform exhibited a log-linear detection range from 0.1 to 10000 ng·L-1 with a detection limit of 0.034 ng·L-1, significantly below the WHO safety threshold (1 μg·L-1). It demonstrated exceptional robustness, pH tolerance, storage stability, and selectivity against MC-YR/RR/LA. Field validation across six representative sites along a small watershed of the Yangtze River Basin was conducted in complex matrices, with Bland-Altman analysis confirming statistical equivalence to HPLC. This work not only pioneers a defect-aptamer coengineering strategy to reconfigure Z-scheme charge dynamics but also develops a FiDe PEC device enabling on-site accurate quantification of MC-LR, ultimately empowering proactive water quality management and public health protection.