A zinc oxide–silver nanocomposite-based SERS nanoplatform for ultrasensitive ofloxacin determination in beef and an ophthalmic solution: effects of ZnO and ZnO content on electron transfer and SERS enhancements

Surface-Enhanced Raman Scattering (SERS) is a powerful analytical tool, which is usually based on the use of noble metal nanoparticles. To further improve the performance of SERS sensors, the substrates have been modified, leading to the design and development of metal-semiconductor nanocomposites. In this work, a series of zinc oxide-silver (ZnO/Ag) nanocomposites with different ZnO contents were prepared and employed for Raman measurements of ofloxacin (OFL) to evaluate their SERS performance. By comparing their SERS sensing performance, the effects of ZnO and ZnO content were clarified. With the most optimal ZnO content of 16 wt%, the ZnO/Ag-based SERS sensor could detect OFL at concentrations ranging from 10^-3 M to 10^-11 M in standard solutions, achieving an ultralow limit of detection (LOD) of 1.5 × 10^-11 M. The SERS signal of OFL on ZnO/Ag substrate has been improved with the EF calculated to be 1.8 × 10⁶, which is about 10 times higher than on pure AgNPs (1.7 × 10⁵). This impressive enhancement was achieved by the effects of Ag (electromagnetic and chemical enhancement) and ZnO (adsorption), individually, as well as the combining effects of the two components (additional electromagnetic enhancement and charge transfer). Furthermore, the advanced SERS sensor based on ZnO/Ag nanocomposite substrate could determine OFL content in beef and a commercial OFL ophthalmic solution.