Smartphone-assisted hydrogel platform based on BSA-CeO2 nanoclusters for dual-mode determination of acetylcholinesterase and organophosphorus pesticides

A dual-mode sensor was developed for detecting acetylcholinesterase (AChE) and organophosphorus pesticides (OPs) via bifunctional BSA-CeO2 nanoclusters (NCs) with oxidase-mimetic activity and fluorescence property. The dual-mode sensor has the characteristics of self-calibration and self-verification, meeting the needs of different detection conditions and provide more accurate results. The colorimetric sensor and fluorescence sensor have been successfully used for detecting AChE with limit of detection (LOD) of 0.081 mU/mL and 0.056 mU/mL, respectively, while the LOD for OPs were 0.9 ng/mL and 0.78 ng/mL, respectively. The recovery of AChE was 93.9-107.2% and of OPs was 95.8-105.0% in actual samples. A novel strategy was developed to monitor pesticide residues and detect AChE level, which will motivate future work to explore the potential applications of multifunctional nanozymes.

Achieving smartphone-based colorimetric assay for Hg2+ with a bimetallic site strategy based on Hg2+-triggered oxidase-like catalytic activity of NSC/Co6Ni3S8 nanocomposite

Modulation of the nanozyme's catalytic activity is crucial for its real applications in detecting target analytes. Herein, we fabricated the nanocomposite (NSC/Co6Ni3S8) of N, S co-doped carbon and Co6Ni3S8 by a facile sol-gel approach. Compared to NSC/Ni9S8, NSC/Co6Ni3S8 with bimetallic active sites displayed better enzyme-mimetic activity. This nanocomposite could catalyze O2 to form ·O2- and oxidize colorless 3, 3', 5, 5'-tetramethylbenzidine (TMB) into blue oxTMB. The other two free radicals (h+ and ·OH) played minor roles during the catalytic reaction. Hg2+ could integrate with S2- to form HgS and the surface charges of O2 were transferred to Hg2+ to promote O2 adsorption. DFT theoretical calculations highlight that the main reasons for the enhancing effect of Hg2+ on color development results from electron transfer and increased adsorption energy of O2 molecules onto the surface of NSC/Co6Ni3S8. By employing the oxidase-like activity of NSC/Co6Ni3S8 and Hg2+-triggered promoting effect, a colorimetric sensing platform was established for Hg2+ assay with a linear range of 10-200 μg/L and detection limit of 3 μg/L. Through integration with a smartphone-based APP "Thing Identify" software, a visual colorimetric assay for Hg2+ was constructed with a detection limit of 5 μg/L. Compared to the data detected by the mercury vapor meter, the relative recoveries of 92.4-108.1% evidenced the higher accuracy of this smartphone-based visual detection. Overall, the NSC/Co6Ni3S8-based colorimetric assay is convenient, rapid, and visual, and can be applied for routine monitoring of Hg2+ in real-world waters under outdoor conditions.