Ultrasensitive photoelectrochemical aptasensor for sulfadiazine detection enhanced by taxifolin-boosted 3D porous g-C3N4.

Photoelectrochemical (PEC) sensing based on graphitic carbon nitride (g-C3N4) has promising attention due to its low background signal; however, its performance is hindered by charge carrier recombination. Herein, a high-performance PEC aptasensor was developed for ultrasensitive sulfadiazine (SDZ) detection using taxifolin-functionalized three-dimensional porous g-C3N4 (T/3DCN) nanosheet. The 3DCN substrate was first synthesized via supramolecular self-assembly using an ionic liquid as a template, followed by thermal polycondensation. Subsequently, taxifolin-rich molecules in hydroxyl groups were covalently incorporated onto the 3DCN surface through a solvothermal process. The doping of taxifolin boosted the visible-light absorption range, significantly promoting charge separation and transfer. The T/3DCN slurry was deposited onto an ITO electrode as a photoactive platform, and the SDZ-specific aptamer was immobilized. Upon SDZ binding, the aptamer-SDZ complex facilitated electron transfer on the electrode surface, generating a "signal-on" response. The sensor exhibited an excellent linear range of 0.1-150 nM, a low detection limit of 52 pM (S/N = 3), and excellent selectivity, reproducibility, and stability. It was successfully applied to detect SDZ residue in Yangtze River water and milk with a recovery of 99.7%-103.2%. This work provides a novel strategy for designing efficient metal-free photoactive materials for monitoring environmental pollutants.