Abstract
We report magnetic silver nanoshells (M-AgNSs) that have both magnetic and SERS properties for SERS-based detection. The M-AgNSs are composed of hundreds of Fe3O4 nanoparticles for rapid accumulation and bumpy silver shell for sensitive SERS detection by near-infrared laser excitation. The intensity of the SERS signal from the M-AgNSs was strong enough to provide single particle-level detection. We obtained much stronger SERS signal intensity from the aggregated M-AgNSs than from the non-aggregated AgNSs. 4-Fluorothiophenol was detected at concentrations as low as 1 nM, which corresponds to 0.16 ppb. The limit of detection for tetramethylthiuram disulfide was 10 μM, which corresponds to 3 ppm. The M-AgNSs can be used to detect trace amounts of organic molecules using a portable Raman system.
Highlights
Surface-enhanced Raman scattering (SERS) has been widely utilized as a powerful tool for molecular analysis because of its narrow bandwidth and stability against photobleaching [1–5]
To obtain different ranges of the absorption spectrum, various shaped nanostructures based on Ag or Au NPs were prepared by conducting galvanic replacement reaction [11,12]
SERS enhancement factor (EF) for a 4-FBT-treated M-AgNS was estimated using the following equation: EF = (ISERS/NSERS)/(Inormal/Nnormal), where ISERS and Inormal are the intensity of the bands from SERS and normal Raman scattering, respectively, and Nnormal and NSERS are the number of
Summary
Surface-enhanced Raman scattering (SERS) has been widely utilized as a powerful tool for molecular analysis because of its narrow bandwidth and stability against photobleaching [1–5]. These nanostructures, especially Ag NPs, exhibited specific absorption spectra depending on the concentration of HAuCl4 As another nanostructure for effective generation of SERS signal, metal nanoshells attracted lots of Nanomaterials 2017, 7, 146 interests [13,14]. The non-remanence magnetization is attributed to the individual Fe3O4 NP (18 nm), which are small enough to maintain superparamagnetic property [43] This can explain the observed superparamagnetic behavior of the M-AgNSs. the saturation magnetization of M-AgNSs can be interpreted in terms of the number of individual Fe3O4 NPs and the total mass of M-AgNS. M-AgNS has 400 times stronger response than individual Fe3O4 NPs, maintaining superparamagnetic property, and M-AgNSs were strongly attracted by a magnet within 5 min (Figure 2f)
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