Switchable aptamer-fueled colorimetric sensing toward agricultural fipronil exposure sensitized with affiliative metal-organic framework.

Persistent usage of pesticides in agriculture has posed serious damage to overall ecosystem and human health, and thereby it is imperative to develop sensitive and efficient tools to evaluate residual pesticides in food and environmental setting. Herein, we reported a switchable colorimetric probe toward fipronil residue sensitized with aptamer-fueled catalytic activity of affiliative ZIF-8. Innovatively, it was found that the attached aptamer preferred to adsorb 3,3',5,5'-tetramethylbenzidine (TMB) rather than 2,2-azinobis (3-ethylbenzothiazo-line-6-sulfonic acid) (ABTS), greatly promoting catalytic oxidation of ZIF-8 toward TMB for further improving sensitivity. Aiding with smartphone-based image acquisition, fipronil-responsive discoloration degree was converted into the ratio of green and blue (G/B) with limit of detection as low as 0.036 µM (0.016 µg·g-1). Moreover, it allowed for fipronil analysis in water, soil and vegetable samples with good recovery between 87 % and 110 %, verifying extension application prospect of the aptamer-fueled colorimetry for on-field pesticide evaluation in food safety supervision.

Single-step electrochemical sensing of ppt-level lead in leaf vegetables based on peroxidase-mimicking metal-organic framework.

A simple and sensitive electrochemical sensor was established for monitoring parts-per-trillion (ppt)-level lead in leaf vegetables based on Pb2+-dependent DNAzyme and porphyrin-functionalized metal-organic framework (porph@MOF). Especially, the prepared porph@MOF showed excellent peroxidase-mimicking activities and also exhibited high stability in a wide range of temperature and pH. Using porph@MOF as mimic catalyst for sensing construction, the limit of detection for Pb2+ analysis was found to be 5 pM (corresponding to 1 ppt by weight), which was quite qualified for the regular monitoring of lead pollution in leaf vegetables. Moreover, the proposed principle facilitated the anti-jamming assay due to the specific recognition behavior of DNAzyme to Pb2+, and could be applied to detect Pb2+ in presence of the interfering metal ions. When compared with multiple-operation approaches, this sensor was constructed with single-step protocol, thereby greatly simplifying the analytical process and enhancing the temporal efficiency. With these merits of simplicity, rapid response, high sensitivity and specificity, the electrochemical sensor offered a promising means for evaluating the safety of leaf vegetables polluted with lead.