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.