Construction of a Photonic Crystal (PC) Film Sensing Platform Based on Calcium Alginate Hydrogel for the Trichlorfon Detection

Trichlorfon, an organophosphorus pesticide widely used in agriculture and other fields, poses a severe risk to both food safety and human health. We developed a photonic crystal film sensing platform for detecting trichlorfon, a hazardous organophosphorus pesticide. The method exploits trichlorfon’s inhibition of acetylcholinesterase (AChE). Normally, AChE catalyzes acetylcholine hydrolysis to produce acetic acid, which decomposes CaCO3 to release Ca2+. This triggers calcium alginate hydrogel formation, increasing solution viscosity and trapping water. When trichlorfon inhibits AChE, hydrogel formation fails, leaving the solution in a low-viscosity sol state with abundant free water. Immersing the film in trichlorfon-containing sodium alginate solutions causes water absorption and film swelling due to free water. Higher trichlorfon concentrations reduce hydrogel formation, increase free water, and amplify film swelling, resulting in proportionally higher reflectivity. The platform demonstrates a wide linear range (1–250 ng/mL) and a low detection limit (0.4 ng/mL) for trichlorfon. Successful analysis of real samples confirms its practicality for residue detection. This label-free thin-film sensor shows significant potential for monitoring trichlorfon and other organophosphorus pesticides.