Magnetic-based silver composite microspheres with nanosheet-assembled shell for effective SERS substrate

Abstract

Well-dispersed magnetic-based silver composite microspheres (Fe₃O₄@SiO₂@Ag) with a nanosheet-assembled shell structure were synthesized at room temperature, where sonicating and mechanical stirring techniques were both employed and played important roles during the silver shell growth process. The results show that the nanosheet-assembled silver shell could be obtained and controlled by adjusting the concentration of citrate ions as a morphology directing-reagent. The gaps in or between cross-linked nanosheets in the shell of the composite microspheres were proposed to provide sufficient “hot spots” when they were used as a SERS substrate. The SERS measurements exhibit clear enhancement signals by using R6G as a probe molecule, and even at concentrations as low as 10⁻¹⁴ M, all enhancement peaks could be observed clearly. The film assembled from the composite microspheres exhibited good reproducibility across the entire area. Additionally, the magnetic Fe₃O₄@SiO₂@Ag microspheres can be separated from solution rapidly, which shortened the detection time. Considering their excellent SERS performance, this kind of composite microsphere, which has both a SERS active shell and a magnetically separable core, would be very useful as an effective SERS substrate for detecting organic pollutants in solution.