An "on-off-on" photoelectrochemical aptasensor using CoO as a signal label for T-2 toxin detection.

T-2 toxin, a mycotoxin commonly found in food, is recognized as one of the most harmful contaminants. Herein, a sensitive photoelectrochemical (PEC) aptasensor based on an "on-off-on" signal response strategy was developed for T-2 detection using WO3/CdIn2S4 as a photoanode. The sensitization of WO3 with CdIn2S4 significantly enhanced the photocurrent, leading to the initial "signal-on" state. As a signal label of probe DNA (pDNA), CoO significantly inhibited the photocurrent response of WO3/CdIn2S4 ("signal-off" state), enhancing the signal recovery space and improving the detection sensitivity. T-2 toxin is preferentially bound to aDNA, releasing the CoO-pDNA complex from the electrode, realizing the "signal-on" state again. This signal switching mechanism enabled a broad detection range from 1 fg mL-1 to 1 μg mL-1 with an ultralow detection limit of 0.434 fg mL-1 (S/N = 3), while the sensor exhibited excellent reproducibility, stability and selectivity. This platform not only provided a robust analytical tool for T-2 toxin detection in food safety but also established a generalizable sensing paradigm adaptable to other mycotoxins by replacing the recognition element.