An Exonuclease I-Assisted Silver-Metallized Electrochemical Aptasensor for Ochratoxin A Detection

Ochratoxin A (OTA)-a mycotoxin produced by Aspergillus and Penicillium fungi-is a carcinogen and common trace contaminant in agricultural and processed food products. As consumption is detrimental to human and animal health, regular product monitoring is vital, and highly sensitive and portable OTA sensors are necessary in many circumstances. Herein, we report an ultrasensitive, electroanalytical aptasensor for precise determination of OTA at trace levels. The sensor leverages a DNA aptamer to capture OTA and silver metallization as a signal enhancer. Exonuclease I is used to digest unbound aptamers, engendering excellent background signal suppression and sensitivity enhancements. Efficient optimization of assay conditions is achieved using central composite design (CCD), allowing rapid evaluation of both the electrode and square wave voltammetry parameter space. The sensor exhibits excellent analytical performance, with a concentration limit of detection of 0.7 pg mL^-1, a limit of quantitation of 2.48 pg mL^-1, and a linear dynamic range ( R² = 0.968) of over 6 orders of magnitude (between 1 pg mL^-1 and 0.1 μg mL^-1). Direct comparison with ultraperformance liquid chromatography (UPLC) indicates excellent analytical performance for standard solutions ( R² = 0.995) and spiked beer samples ( R² = 0.993), with almost quantitative recovery and less than 5% relative standard deviation (RSD).