Hierarchically porous coralloid ZnO@Ag microspheres as SERS substrate for highly sensitive malachite green detection

Abstract

The improper management and unreasonable use of malachite green (MG) in aquatic transportation and large-scale aquaculture pose a significant threat to human health. It is crucial to develop a rapid and reliable approach for detecting MG. In this study, hierarchically porous coralloid ZnO@Ag (C–ZnO@Ag) microspheres were developed as a surface-enhanced Raman scattering (SERS) substrate to detect MG content in water. The hierarchical and porous structure supporting plenty of Ag nanoparticles provides numerous “hot spots” to excite the strong enhanced local electromagnetic field for enlarging the Raman signals of analytes. Moreover, C–ZnO@Ag generates an additional pathway to improve the charge transfer between the substrate and analytes. The manifold mechanisms resulted in the Raman enhancement factor as high as 1.61 × 107 when R6G was selected as the probe. The MG solution at an ultralow concentration of 10−9 M can be successfully identified using the C–ZnO@Ag substrate, which is much lower than the maximum MG residual concentration in water set by the European Union. Therefore, the C–ZnO@Ag substrate has promising opportunities to be applied in rapid SERS-based detection of toxic organic residues.