Background: Pesticide residues can cause chronic toxicity to the human body and lead to a series of diseases that damage the liver. Therefore, developing a highly sensitive, selective, and low-cost pesticide residues detection method is of great significance for protecting human health and safety. Nowadays, commonly used methods for pesticide residue detection include gas chromatography, high-performance liquid chromatography, and fluorescence sensing. These methods have some typical shortcomings, such as long sample pretreatment time, expensive instruments, and poor controllability. It was thought that a sensing platform based on electrochemical analysis method and functional DNA molecules can eliminate the above drawbacks. Results: Herein, this study developed a simple and label-free electrochemical aptasensor based on a triple- stranded DNA molecular switch. Acetamiprid (ACE) was served as the analytical model, and its binding with the aptamer opened the triple-stranded DNA molecular switch, resulting in the in-situ formation of G-quadruplex/hemin complexes on the electrode surface, obtaining a significantly enhanced electrochemical signal and achieving high specificity and label-free detection of ACE, with a detection limit as low as 4.67 x 10-3 nM (S/N = 3). In addition, due to the specific recognition between the aptamer and the target, the aptasensor effectively avoided the interference of other pesticides and exhibited good specificity. Moreover, benefiting from the pH switchable of the triple-stranded DNA molecular switch and the programmability of DNA molecules, OR logic gate and OR-INHIBIT cascade logic circuit were successfully implemented. Significance: The proposed electrochemical aptasensor exhibited good accuracy and sensitivity in detecting acetamiprid in vegetable soil sample, indicating its practicality in the detection of pesticide residues in actual samples. Furthermore, the sensing system was reasonably programmed and successfully operated an OR logic gate and an OR-INHIBIT cascade logic circuit, demonstrating its potential application in intelligent sensing.

Background: As a broad-spectrum tetracycline antibiotic, Oxytetracycline (OTC) was widely used in a variety of applications. But, the overuse of OTC had led to the detection of it in food, water and soil, which could present significance risk to human health and cause damage to ecosystem. It was of great significance to develop sensitive detection methods for OTC. Herein, an environmentally friendly photoelectrochemical (PEC) aptasensor was constructed for the sensitive detection of OTC based on CuO-induced BiOBr/Ag 2 S/PDA (Polydopamine) photocurrent polarity reversal. Results: BiOBr/Ag 2 S/PDA composites modified electrode not only produced stable initial anodic photocurrent but also provided attachment sites for the aptamer S1 of OTC by the strong adhesion of PDA. On the other hand, CuO loaded OTC aptamer S2 (Cu -S2) was got through Cu -S bonds. After the target OTC was identified on the electrode surface, CuO was introduced to the surface of ITO/BiOBr/Ag 2 S/PDA through the specific binding of OTC to S2. This identification process formed dual Z -type heterojunctions and resulted in a remarkable reversal of photocurrent polarity from anodic to cathodic. Under optimization conditions, the PEC aptasensor showed a wide linear range (50 fM - 100 nM), low detection limit (1.9 fM), excellent selectivity, stability and reproducibility for the detection of OTC. Moreover, it was successfully used for the analysis of OTC in real samples of tap water, milk and honey, and had the potential for practical application. Significance: This work developed an environmentally friendly photocurrent-polarity-switching PEC aptasensor with excellent selectivity, reproducibility, stability, low LOD and wide linear range for OTC detection. This sensitive system, which was including BiOBr, Ag 2 S, PDA and CuO were low toxicity, not only reduced the risk of traditional toxic semiconductors to operators and the environment, but can also be used for the detection of real samples, broadening the wider range of applications for BiOBr, Ag 2 S, PDA and CuO.