Bioenzyme-nanoenzyme-chromogen all-in-one test strip for convenient and sensitive detection of malathion in water environment.

The presence of pesticide residues in aquatic environments poses a significant threat to both aquatic ecosystems and human health. The presence of these residues can result in significant harm to aquatic ecosystems and can negatively impact the health of aquatic organisms. Consequently, this issue requires urgent attention and effective measures to mitigate its impact. However, developing sensitive and rapid detection methods remains a challenge. In this study, an all-in-one test strip, which integrated bioenzymes, nanoenzymes, and a chromogen, was developed in combination with an enzyme labeling instrument for a highly sensitive and convenient sensing of malathion residues. The oxidase activity of heme chloride (Hemin) in the strip can catalyze the oxidation of H2O2 and 3,3',5,5'-tetramethylbenzidine (TMB) to produce a blue-colored oxide. Simultaneously, the alkaline phosphatase (ALP) present in the strip can break down l-ascorbic acid-2-phosphate to produce ascorbic acid (AA). This AA then acts to reduce the oxidized form of TMB, turning it into a colorless substance and leading to the disappearance of its fluorescent signal. In the presence of a pesticide, the activity of ALP is inhibited and formation of AA is blocked, thereby preventing the reduction of oxidized TMB and producing a colored signal. According to this principle, the integrated test strip detected the target pesticide with high performance as per the optical density value determined via an enzyme marker. The detection limit of the test strip was 0.209 ng/mL with good sensitivity. The method was used for detecting malathion in actual river water samples, and the recoveries were in the range of 93.53 %-96.87 %. The newly devised technique effectively identified malathion in samples of natural water. This research has introduced a novel approach for the precise and convenient surveillance of pesticide remnants. Additionally, these discoveries could inspire the advancement of proficient multi-enzyme detection systems.

A dual-optical sensor for mancozeb by UCNP@PVP@MnO2 nanozyme.

In this work, a fluorescence/colorimetric dual-mode detection method based on MnO2 nanoflower-decorated upconversion nanoparticles: NaYF4:Yb/Er@polyvinylpyrrolidone@MnO2 (UCNP@PVP@MnO2) was proposed to detect the presence of mancozeb (MB). In this detection system, the MnO2 nanoflowers in the nanocomplex of UCNP@PVP@MnO2 would quench the fluorescence of the UCNP. With the addition of H2O2 and 3,3',5,5'-tetramethylbenzidine (TMB), the reaction between MnO2 and H2O2 resulted in the dissolution of MnO2 and the dissolution of the MnO2 layer contributed to the fluorescence recovery of UCNP. Simultaneously, MnO2 oxidized the colorless TMB to a blue product oxidized 3,3',5,5'-tetramethylbenzidine (oxTMB). The blue solution was able to quench the recovered fluorescence of UCNP due to the fluorescence inter filter effect (IFE) between the UCNP and blue oxTMB. Finally, with the addition of MB, the oxTMB was reduced to TMB by MB and the color of the solution became lighter while the fluorescence intensity of the solution increased. The detection method had a good linear range of 5-120 µM and 0.5-60 µM for fluorescence and colorimetric detection, respectively, and the limits of detection (LOD) were 2.34 and 0.245 µM, respectively.