Enzyme-Induced Signal Cycling Amplification on a FET-Based POCT Biosensor for Ultrasensitive Tetracycline Detection in Food and Environmental Samples

Tetracycline (TC), a widely used broad-spectrum antibiotic, poses severe risks to human health through environmental leakage (soil and water) and food chain transmission. However, the low concentration of TC in environmental samples and the complexity of sample matrices pose significant challenges for its rapid, sensitive, and on-site detection. Here, we present a portable point-of-care testing (POCT) device for on-site determination of TC, based on a DNA-functionalized field-effect transistor (FET) biosensor. By implementing an Exonuclease III (Exo III)-assisted cycling amplification strategy on the FET surface, the biosensor efficiently recognizes trace TC and amplifies the signal through consecutive release of reporter probes during nicking reactions. Under optimal conditions, the FET biosensor achieves a wide linear range from 1 pM to 1 μM, a low detection limit of 0.3 pM and completes ultrasensitive detection within 70 min. A rapid microfluidic channel is also designed to transport water samples efficiently and provide reaction zones for recognition and signal amplification. When connected to a printed circuit board and a mobile application via Bluetooth, the proposed system can rapidly report TC levels on-site, demonstrating good accuracy and reliability in river water, milk, and honey samples. This work paves the way for integrated, ultrasensitive detection of antibiotic pollutants, offering a powerful and portable POCT device for early warning and source tracing of pollutant leakage.