Label-Free Electrochemical Sensor for Ochratoxin A Using a Microfabricated Electrode with Immobilized Aptamer

Ochratoxin A (OTA) is one of the most abundant food-contaminating mycotoxins that is also a potential carcinogen and responsible for many diseases affecting humans. Consequently, a sensitive, portable device for the detection of OTA is highly desirable. In this study, a miniaturized electrochemical aptamer-based sensor was developed for the label-free, sensitive detection of OTA. For the construction of the sensor, a gold thin-film three-electrode system was fabricated using standard microfabrication techniques on a polystyrene substrate (25 mm × 25 mm). Subsequently, the thiol-modified linker, 6-mercaptohexanol, DNA aptamer, and methylene blue (MB) were sequentially applied to the working electrode to construct a sensing layer. MB served as a redox indicator that interacted with the aptamer via the guanine bases and phosphate backbone to form complexes. The addition of OTA to the sensor induced the folding of the aptamer, which was accompanied by the release of the aptamer–MB–OTA complex from the sensor. Thus, the amount of MB decreased with increasing concentration of OTA. Differential pulse voltammetry was used for monitoring the highly sensitive detection. The standard curve for OTA exhibited a wide linearity ranging from 0.1 to 300 ng mL–1 with a detection limit of 78.3 pg mL–1 (S/N = 3). The selectivity test confirmed that the aptamer had high affinity only for the target. The OTA recoveries with the proposed sensor in commercial samples of coffee and beer were 86.4–107%