Facile one-step synthesis of Ag anchoring on Cu2O for enhanced SERS activity: Efficient charge transfer and adsorption

There is a keen research interest to develop inexpensive and ultrasensitive substrate materials for practical sensing application of surface enhanced Raman spectroscopy (SERS). Aiming to utilize synergistic enhancement contributions originated from plasmon adsorption and charge transfer (CT), it is highly desirable to construct hybrid substrates of noble metals and semiconductors. In this work, Ag nanoparticles-decorated Cu2O hybrids (Ag- Cu2O) were synthesized through a simple one-step growth method, i.e., reducing AgNO3 and CuCl2 by ascorbic acid (AA) in the presence of PVP. A systematic study has been carried out to characterize the material properties and SERS performance of Ag-Cu2O hybrids prepared under different molar ratios of precursors, growth temperatures and addition speed of reducing agent. Ag-Cu2O hybrids, composed of well-distributed Ag nanoparticles on Cu2O nanoplates, showed enhanced SERS performance in comparison with pure Cu2O. When 4-nitrobenzenethiol (4-NBT) was used as probe molecule, the optimal sample showed a calculated enhancement factor of 1.4 x 105 and a low detection of limit (LOD) of 1 x 10-10 M, which is four orders of magnitude lower than that of pure Cu2O. Ag-Cu2O hybrid substrates can also be used to detect dye molecues and the LODs for rhodamine 6G and crystal violet were 1 x 10-8 M and 1 x 10-9 M, respectively. It is feasible that the observed enhancement of SERS activity were benefited from synergistic contributions of the abundant "hot spots", rich photo-induced charge transfer pathways, improved adsorption ability, and suppressed recombination of e-h pairs in Ag-Cu2O hybrids. This work provides a simple and controllable approach to fabricate metal/semiconductor hybrids as SERS sensing platform.