Mesoporous Ce/Zn Oxide Nanospheres with Prominent Oxidase-Like Activity for Reliable Tracking of the Cartap Residue and S ^2– in Living Agricultural Products

A mesoporous Ce/Zn oxide nanozyme (Ce/Zn ONN) was developed for portable tracking of the cartap residue and toxic S^2- in agricultural products. Ce/Zn ONN possessed a high specific surface area of 107.87 m²·g^-1 and superior oxidase-mimic activity to promote the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) with a <i>K</i>_m/<i>V</i>_max of 0.24 mM/4.07 × 10^-8 M/s. Under optimized oxidase-mimic conditions, trace cartap or S^2- could deteriorate the color of Ce/Zn ONN-TMB with a clear hypochromic effect, from blue to colorless. With the help of a smartphone APP, Ce/Zn ONN-TMB was applied for dual-mode ultraviolet-visible (UV-vis) and red-green-blue (RGB) tracking of the cartap residue and S^2- in agricultural products. The detection limits (LODs) were 3.84 × 10^-8/3.68 × 10^-7 g/mL for ultraviolet-visible (UV-vis)/RGB detection of cartap with the relative standard deviation (RSD%) of less than 3.12%/3.25% and 3.15 × 10^-8/5.62 × 10^-8 M for S^2- with RSD% of less than 3.54%/3.87% respectively. Moreover, cartap degradation results in living vegetables could be tracked, and the recognition mechanisms were proposed as well.