Ultrasensitive detection of tetracycline by the g-C₃N₄/Ag/UiO-66-NH₂ Z-type heterojunction-binding enzyme biosensor

Tetracycline (TC) is a persistent broad-spectrum antibiotic that poses significant threats to human health and the environment. Herein, we developed an ultrasensitive photoelectrochemical (PEC) biosensor for rapid TC detection. The sensor utilizes a flexible Si-doped carbon fiber membrane derived from polyacrylonitrile and dimethyldiethoxysilane as a conductive substrate. After coating with poly (3,4-ethylenedioxythiophene) and polystyrene sulfonate (PEDOT: PSS), a ternary UiO-66-NH₂/Ag/g-C₃N₄ Z-scheme heterojunction is assembled as the photoactive core, followed by electrostatic immobilization of laccase to achieve specific TC recognition. Electrochemical characterization confirmed that laccase improved both the biocatalytic activity and electron-transfer efficiency of the electrode. Combined with transient photocurrent measurements and molecular dynamics simulations, the sensing mechanism was shown to be dominated by steric hindrance arising from TC occupation of the laccase active site, followed by oxygen consumption, yielding a detection limit of 0.012 μM over 0-30 μM TC (R² = 0.993). UV diffuse reflectance spectra (UV-DRs), Mott-Schottky analysis (M-S), and electron paramagnetic resonance (EPR) measurements further verified that the Ag-mediated Z-scheme pathway significantly enhanced carrier separation. With excellent stability and anti-interference performance in real river water and complex matrices, this work provides an effective strategy for antibiotic detection by integrating flexible carbon-based substrates with advanced Z-scheme photocatalytic systems.