Biosensor with enhanced photoelectrochemical activity based on heterogeneous Co3O4@C/TiO2 composite with efficient photogenerated carrier separation for chlorpyrifos detection

Photoactive materials with heterostructures are highly effective for photoelectrochemical (PEC) detection. In this study, a honeycombed Co3O4@C was fabricated by calcining the metal-matrix complex of Co(NO3)2/Mel (melamine). Thereafter, the photoactive TiO2 particles were coupled with Co3O4@C to obtain a heterogeneous Co3O4@C/TiO2 composite based on matching band gaps. Under visible-light illumination, the Co3O4@C/TiO2/ ITO modified electrode exhibited superior PEC response compared with Co3O4@C/ITO and TiO2/ITO electrodes. The enhanced PEC response can be attributed to the honeycombed and thin-shelled Co3O4@C, which boosted the visible-light harvesting capacity. Meanwhile, the high porosity on Co3O4@C facilitated infiltration to the elec-trolyte and increased the electronic transportation efficiency. The p-n-type heterojunction interface between the Co3O4@C and TiO2 enhanced the migration of the photo-induced e -/h +/- pair by preventing their recombination. Furthermore, acetylcholine esterase (AChE) was assembled on the chitosan (CS)/glutaraldehyde (GLD)-modified Co3O4@C/TiO2/ITO electrode surface to realize a PEC sensing platform (AChE/CS-GLD/Co3O4@C/TiO2/ITO). Acetylcholine chloride (ATCl) was hydrolyzed using AChE to produce a thiocholine biomolecule, which behaved as an electron donor and generated a photocurrent signal. However, when the bio-recognition component of AChE was suppressed by chlorpyrifos, the reduced production of thiocholine weakened the photocurrent output. Under optimal conditions, proposed sensor is effective for testing chlorpyrifos owing to its high sensitivity. The sensor has a wide linear range of 0.0001-225 mu g mL-1 and a low detection limit (2.9x10-5 mu g mL-1). The sensing platform also has high specificity, reproducibility, and stability. This study developed a photoactive material using a p-n-type heterojunction for application to the development of efficient sensors.