Highly Selective Colorimetric Detection of Cu²⁺ Using EDTA-Complexed Chlorophyll-Copper/ZnO Nanorods with Cavities Specific to Cu²⁺ as a Light-Activated Nanozyme

In this study, chlorophyll-copper (ChlCu)-modified ZnO nanorods (ChlCu/ZnO) were prepared, and then sodium ethylenediamine tetraacetate (EDTA) was used to remove part of Cu2+ in ChlCu, leaving cavities with specific adsorption activity for Cu2+ in E-ChlCu/ZnO. Appropriate EDTA treatment improved the photoactivity of ChlCu/ZnO and the adsorption selectivity to Cu2+. However, excessive EDTA treatment might lead to the collapse of the ChlCu structure, resulting in a decrease in photoactivity. The E-ChlCu/ZnO sample with 8 h of ChlCu treatment and 2 h of EDTA treatment showed optimal photoactivity. The as-prepared E-ChlCu/ZnO exhibited activity as a light-activated nanozyme, which could oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) to blue under illumination, but when Cu2+ was present in the solution, this colorimetric reaction was inhibited; therefore, E-ChlCu/ZnO could be used for colorimetric detection of Cu2+. Because of the existence of specific cavities, E-ChlCu/ZnO showed excellent detection selectivity, a wide linear detection range (0–1 and 1–15 μM), and a low detection limit (0.024 μM) in the colorimetric detection of Cu2+.