A dramatic visible light photoelectrochemical sensing platform for the detection of pesticide molecules at zero potential (versus saturated calomel electrode) was first constructed using poly(3-hexylthiophene)-functionalized TiO(2) nanoparticles. Poly(3-hexylthiophene) (P3HT) was synthesized via chemical oxidative polymerization with anhydrous FeCl(3) as the oxidant, 3-hexylthiophene as the monomer, and chloroform as the solvent, and the functional TiO(2) nanoparticles were facilely prepared by blending TiO(2) nanoparticles and P3HT in chloroform solution. The resulting photoelectrocatalysts were characterized by scanning electron microscopy, Raman spectroscopy, and X-ray diffractometry. Under visible light irradiation, P3HT generated the transition from the valence band to the conduction band, delivering the excited electrons into the conduction band of TiO(2) and then to the glassy carbon electrode. Simultaneously, a positive charged hole (h(+)) of TiO(2) may form and migrate to the valence band of P3HT, which can react with H(2)O to generate (•)OH, and then it converted chlopyrifos into chlopyrifos(•) that promoted the amplifying photocurrent response. On the basis of the proposed photoelectrochemical mechanism, a methodology for sensitive photoelectrochemical sensing for chlopyrifos at zero potential was thus developed. Under optimal conditions, the proposed photoelectrochemical method could detect chlopyrifos ranging from 0.2 to 16 μmol L(-1) with a detection limit of 0.01 μmol L(-1) at a signal-to-noise ratio of 3. The photoelectrochemical sensor had an excellent specificity against the other pesticides and could be successfully applied to the detection of reduced chlopyrifos in green vegetables, showing a promising application in photoelectrochemical sensing.