Uniform MF/Ag-NPs core–shell composite microspheres as isolated SERS substrates for quick and sensitive detection of insecticide

Abstract

Uniform MF/Ag-NPs core–shell composite microspheres were fabricated as isolated SERS (surface-enhanced Raman scattering)-active substrates through coating of Ag nanoparticles (Ag-NPs) onto MF (melamine formaldehyde resin) microspheres. These composite microspheres can be imaged and individually manipulated under an optical microscope. Their SERS spectra can be taken at the focal point to ensure the best analysis result or to recognize the identity of the microsphere for flow cytometry. In this paper, the SERS activity of the composite microspheres was evaluated using 4-ABT, 4-CBT, and 4-DTNB as the Raman reporting molecules; the SERS data of tetramethylthiuram disulfide were also acquired on the isolated MF/Ag-NPs core–shell composite microsphere. Due to the significant electromagnetic coupling effect created by the Ag-NPs on the MF microsphere, the SERS detection limits for 4-ABT, 4-CBT, and 4-DTNB were as low as 10⁻⁹ mol L⁻¹, 10⁻¹⁰ mol L⁻¹, and 10⁻⁸ mol L⁻¹, respectively. For the insecticide tetramethylthiuram disulfide, the detection limit was 10⁻⁹ mol L⁻¹ using the isolated MF/Ag-NPs microsphere as the SERS substrate. The SERS signal intensity linearly depended upon the concentration of tetramethylthiuram disulfide, indicating that the MF/Ag-NPs core–shell composite microsphere can be used for quantitative analysis of this insecticide.