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Mercury ion (Hg 2+ ), a bioaccumulating and toxic heavy metal, can cause severe damages to the environment and human health. Therefore, development of high-performance Hg 2+ sensors is highly desirable. Herein, we construct a uniform dodecahedral shaped N-doped carbon decorated by single Fe site enzyme (Fe-N-C SAE), which exhibits good performance for Hg 2+ detection. The N atom on Fe-N-C SAE can specifically recognize Hg 2+ through chelation between Hg 2+ and N atom, while the catalytic site on the single-atom enzyme acts as a signal amplifier. The Fe-N-C SAE-functionalized solution-gated graphene transistor exhibits a dramatic improvement in the selectivity and sensitivity of the devices. The sensor can rapidly detect Hg 2+ down to 1 nM within 2 s. Besides, a relatively good repeatability and reproducibility for the detection of Hg 2+ have also been found in our sensor platform. Our findings expand the application of single-atom catalysts in the field of food safety and environmental monitoring.

Circular DNA aptamers are powerful candidates for therapeutic applications given their dramatically enhanced biostability. Herein we report the first effort to evolve circular DNA aptamers that bind a human protein directly in serum, a complex biofluid. Targeting human thrombin, this strategy has led to the discovery of a circular aptamer, named CTBA4T-B1, that exhibits very high binding affinity (with a dissociation constant of 19 pM), excellent anticoagulation activity (with the half maximal inhibitory concentration of 90 pM) and high stability (with a half-life of 8 h) in human serum, highlighting the advantage of performing aptamer selection directly in the environment where the application is intended. CTBA4T-B1 is predicted to adopt a unique structural fold with a central two-tiered guanine quadruplex capped by two long stem–loops. This structural arrangement differs from all known thrombin binding linear DNA aptamers, demonstrating the added advantage of evolving aptamers from circular DNA libraries. The method described here permits the derivation of circular DNA aptamers directly in biological fluids and could potentially be adapted to generate other types of aptamers for therapeutic applications.

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Background Aflatoxin B1 (AFB1) has been considered as a prevailing natural carcinogenic mycotoxin in various food and feedstuff products, posing serious endangers to human health. The quantitative and selective detection of AFB1 was significantly essential for food safety control. Results We developed a label‐free fluorescent aptasensor using a target‐binding aptamer probe as the rolling circle amplification (RCA) primer for AFB1 detection. In the presence of AFB1, the probe preferentially combined with AFB1 rather than binding to the circular template, inhibiting the initiation of RCA process. The detection limit of the proposed method was as low as 6.6 nM, and the linear dynamic response range was four orders of magnitude wide. Besides, it revealed excellent specificity for AFB1 and high‐quality detection performance in food samples. Conclusion The presented detection method was simple, rapid, and economical, which indicated a promising application in food safety monitoring.