Development of SERS platform based on ZnO multipods decorated with Ag nanospheres for detection of 4-nitrophenol and rhodamine 6G in real samples

Noble-metal/semiconductor-based nanomaterials have attained high Raman enhancement in the surfaceenhanced Raman scattering (SERS) sensor. The fabrication of noble-metal/semiconductor-based SERS substrates with high sensitivity and good reproducibility is a great challenge. Noble-metal nanoparticles on semiconductor have strong capability to resonate the organic molecule adsorbed on them for the SERS enhancement. In this work, silver nanospheres (Ag NSs) decorated on zinc-oxide (ZnO) multipods are produced as a noblemetal/semiconductor-based SERS substrate and the effect of mixing ratio between Ag NSs and ZnO multipods is systemically studied. The optimized Ag/ZnO SERS substrate shows the superior SERS performance for the detection of 4-nitrophenol (4-NP) and rhodamine 6G (R6G). The corresponding limits of detection are 1.49 x 10-13 M and 9.99 x 10- 12 M with the analytical enhancement factor of 4.27 x 1010 for 4-NP and 1.97 x 109 for R6G. The strong SERS enhancement is attributed to the synergistic effect of electromagnetic mechanism and chemical mechanism. Physical and chemical characteristics of Ag/ZnO-multipod structure were studied using field emission scanning electron microscopy, X-ray diffraction, elemental mapping, energy-dispersive X-ray spectroscopy and UV-Vis spectroscopy. The proposed Ag/ZnO-multipod structure has excellent uniformity and reproducibility with the relative standard deviation less than 6%. The real-sample analysis of 4-NP and R6G in river water is experimentally carried out and gives the satisfactory recovery values > 84%. This study reveals that the Ag/ZnO-multipods are practically applicable as a highly sensitive SERS substrate.