Ferrocene-Decorated Covalent Organic Framework/SiO2/Multi-Walled Carbon Nanotube Nanocomposites as a Ratiometric Electrochemical Sensing Platform for Self-Calibrated Detection of Fenitrothion Residues

Accurate and sensitive identification of pesticide residues in food is essential for food safety supervision and risk control. Herein, a ratiometric electrochemical sensing platform based on a ferrocene-decorated covalent organic framework/2D-SiO 2 /MWCNTs nanocomposite (COFs/2D-SiO 2 /Fc/MWCNTs) was constructed for accurate quantification of fenitrothion (FNT). The nanocomposite was synthesized via a mild self-assembly approach, in which 2D-SiO 2 acted as a 2D scaffold to improve the dispersion of COFs and promote the stable immobilization of Fc. The crystalline porous COFs provided abundant sites for FNT enrichment, the firmly immobilized Fc served as a stable internal reference for ratiometric sensing, and the incorporated MWCNTs effectively boosted the conductivity and electrocatalytic activity of the nanocomposite. The obtained COFs/2D-SiO 2 /Fc/MWCNTs nanocomposite showed favorable electrocatalytic performance toward FNT. With the ratiometric signal I FNT /I Fc as the readout, the sensor displayed a linear response from 0.0001 to 50 μg·mL –1 . Compared with conventional single-signal sensors, this ratiometric method enables efficient self-calibration against environmental interference, enhancing the accuracy and reliability of FNT detection in food samples.