Multifunctional Surface-enhanced Raman Scattering Research Articles

Multifunctional Surface Enhanced Raman Scattering Substrate Fe 3O4 @AgNPs@MIL-101 for Pretreatment and Rapid Detection of Pesticide Residues on the Surface of Fruit Peels.

A multifunctional surface-enhanced Raman scattering substrate Fe3O4@AgNPs@MIL-101 was prepared. Rapid SERS detection of pesticide residues was realized by direct pre-enrichment and separation on the peel surface. MIL-101 has an ortho-octahedral framework and large pore size, which endowed Fe3O4@AgNPs@MIL-101 with the ability to rapidly adsorb and separate positively charged targets. The introduction of tannic acid realized the insitu growth of AgNPs on the backbone, to modulate the electromagnetic enhancement. Pesticide molecules were adsorbed onto the surface of AgNPs mediated by central S atoms, accompanied by the interaction between pesticide molecules and AgNPs, the corresponding SERS signals of different pesticides were observed. Together with the introduction of magnetic coating Fe3O4, the molecules were enriched in the hotspot and separated to further enhance the SERS performance. Magnet instead of centrifugation was used to simultaneously perform surface extraction and sample separation for a noninvasive, rapid, immediate, and portable assay. The method was accomplished in measurement of thiram and thiabendazole on apple and tangerine epidermis, and the limits of detection (LODs) were 20 ng/cm2 and 4 μg/cm2, respectively. The recovery was reasonable, and it showed that the procedure is valuable for the rapid and nondestructive surface analysis of residual chemicals.

An ordered fish scale-like Co-TiO2/GO inverse opal photonic crystal as the multifunctional SERS substrate

Nowadays, developing highly sensitive and multifunctional surface-enhanced Raman scattering (SERS) substrates is very significant. Here, a new cobalt (Co)-doped titanium dioxide (TiO2)/graphene oxide (GO) inverse opal photonic crystal (IO PC) was successfully synthesized using polystyrene opal as the template. The scanning and transmission electron microscope images demonstrate the ordered fish scale-like shape while the element mappings display the uniform element distribution of the Co-TiO2/GO IO PC. Raman spectra show that the detection limit of 4-mercaptobenzoic acid (4-MBA) on the Co-TiO2/GO IO PC SERS substrate is as low as 10−12 M, exhibiting better SERS effect than TiO2 and Co-TiO2 IO PCs. Amperometric I-t curves reveal that the photocurrent density of Co-TiO2/GO IO PC is six and three times more than that of TiO2 and Co-TiO2 IO PCs under simulated sunlight irradiation, respectively. Furthermore, UV-Vis spectra indicate that the degradation rate of methylene blue and Congo red over Co-TiO2/GO IO PC photocatalyst could separately reach 96% and 93%, which are much higher than that over TiO2 and Co-TiO2 IO PCs. The outstanding performance of Co-TiO2/GO IO PC was caused by that the Co2+ doping and GO addition broadened the light absorption to visible range, the electron traps resulted from Co2+ doping inhibited the recombination of electron-hole pairs and doping levels promoted TiO2-to-molecule charge-transfer process, which were confirmed by the UV-Vis spectra, PL spectra and SERS spectra, respectively. At the same time the periodic IO PC structure led to multiple scattering of light and improved the light-mass interaction. The prepared Co-TiO2/GO IO PC may be a promising material in SERS effect, water purification and so on.

Multifunctional SERS substrates of Fe3O4@Ag2Se/Ag: construction, properties and application

In this work, Fe3O4@Ag2Se/Ag nanocomposites were fabricated on a self-cleaning and recyclable surface-enhanced Raman scattering (SERS) substrate via a simple and ingenious precipitation shift reaction. The superparamagnetic property of Fe3O4 facilitates the efficient purification of products with the assistance of an external magnetic field. The as-prepared substrates have excellent stability and show no significant loss after six recycles for the photodegradation of rhodamine B (RhB). The unique Raman enhancement effect of Fe3O4@Ag2Se/Ag substrates indicates that RhB can be detected at a concentration as low as 1 × 10−8 M. Furthermore, the experimental results also suggest that these nanocomposites may be promising multifunctional SERS substrate candidates for environmental monitoring, cleaning and so on.