Li-Jun You,Qiao An,Jia Guo,Jack J. Hu,Chang-Chun Wang
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.
Here we demonstrate a novel SERS-active substrate assembled by silver nanowire (Ag NW)-embedded porous polystyrene (PS) fibers. Ag NWs are synthesized through a glycerol-mediated solvothermal method firstly, then electrospun into PS porous fibers. The as-synthesized Ag NWs are embedded in PS fiber and aligned orderly along the axial direction. Porous structure appears in PS fiber due to the phase separation induced by rapid evaporation of solvents. Large amounts of holes not only greatly improve the sample collection efficiency of the SERS-active substrate, but also significantly facilitate the adsorption of target molecules on the surface of Ag NWs, thus increasing the probability of enhancement of target molecules. In addition, compared with polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP), PS has better solvent resistance. The detection limit of 4-aminothiophenol (4-ATP) on our fabricated electrospun fiber mats is 10−7 M, and the electrospun fiber mats showed good reproducibility of SERS signal detection. This study proposes a feasible strategy for the large-scale preparation of flexible SERS-active substrate assembled by Ag NW-embedded porous PS fibers. The produced flexible SERS substrates may have potential application in wearable sensors for the trace detection of chemical and biological molecules.
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