Green and Controllable Synthesis of Au–Ag Bimetal Nanoparticles by Xylan for Surface-Enhanced Raman Scattering

Abstract

In surface-enhanced Raman scattering, Ag nanoparticles are broadly employed. However, their lack of oxidation resistance means that their performance diminishes and is difficult to repeat. In this study, with addition of xylan, Au–Ag core–shell and alloy nanoparticles were prepared. Besides functioning as a reducing and stabilizing agent for Au–Ag bimetal nanoparticles, xylan protected them from oxidation and aggregation and created hot spots between interconnected nanoparticles. By seed-mediated methods, Au–Ag hollow alloy and Au@Ag core–shell nanoparticles with different shell thicknesses were prepared. More spherical and larger core–shell nanoparticles were prepared by an optimized dosage of xylan without the generation of excess Ag nanoparticles. Furthermore, the Au@Ag nanoparticles showed enhanced stability against oxidation and corrosion by H2O2 with the packing of xylan. The Raman enhancement performance of xylan-capped Au@Ag nanoparticles with optimized shell thickness to 4-mercaptobenzoic acid was better than that of Au–Ag alloy, neat Au and Ag nanoparticles. The Au@Ag nanoparticles could detect 4-mercaptobenzoic acid with a greater sensitivity and its limit of detection was 1 nM. Moreover, xylan-capped Au@Ag nanoparticles could detect food contaminant like Sudan I with a limit of detection as low as 0.126 ppm. Therefore, this work not only offers a new method for high-value utilization of xylan but also presents a simple, green, and ultrasensitive surface detection technique for the assessment of food/environmental safety.

Application of Novel Plasmonic Nanomaterials on SERS

“…R6G exhibited an electronic absorption maximum at 530 nm that matched the laser excitation wavelength and also lay close to the SPR of Cu NPs, and so RR effects were expected to be observed for both the bulk solid and adsorbed molecules in our study using a 532-nm laser excitation. As observed by previous researchers, the SERRS effect on Au nanoparticles or roughened Cu surfaces resulted in the appearance of the characteristic Raman peaks of the adsorbed molecules using red (632.8 nm) to blue (488 nm) excitation lines [83,84]. Our data show that the spectrum could be detected down to at least 10 −6 M, where the relative intensities were comparable to those of the bulk solid (Figure 6c).…”

“…These SERS performances were explained by the fact that the xylan capping allowed creating hotspots between Au/Ag nanoparticles. Optimal SERS performances for xylan-capped Au/Ag nanoparticles were realized for a mole ratio of AgNO 3 to HAuCl 4 equal to 4 and a dosage of xylan equal to 1 in the fabrication of Ag shell corresponding to 2.86 × 10 −8 mol of xylan (see Figure 3) [84]. To conclude this section on bimetallic nanosystems, Prakash et al reported on the SERS detection of bacteria by using Au/Ag plasmonic nanoparticles which were positively charged (see Figure 4).…”

A Novel Enzyme‐Free Biosensor for Hydrogen Peroxide Based on Black Phosphorus @Au‐Ag Nanohybrids

“…Compared with BP, the BP@Au composite exhibits four significant peaks at 38.2°, 44.3°, 64.7°and 77.5° and can be assigned to the (111), (200), (220) and (311) Au planes (JCPDS 04‐0784), [30] respectively, confirming that Au nanoparticles are successfully anchored on the surface of BP nanosheets. As against BP@Au, the intensity of the diffraction peaks in BP@Au−Ag nanohybrids is slightly increased, [31] indicating the formation of Ag−Au bimetallic nanoparticles over the BP matrix.…”

Latest Novelties on Plasmonic and Non-Plasmonic Nanomaterials for SERS Sensing

“…These SERS performances were explained by the fact that the xylan capping allowed creating hotspots between Au/Ag nanoparticles. Optimal SERS performances for xylan-capped Au/Ag nanoparticles were realized for a mole ratio of AgNO 3 to HAuCl 4 equal to 4 and a dosage of xylan equal to 1 in the fabrication of Ag shell corresponding to 2.86 × 10 −8 mol of xylan (see Figure 3 ) [ 84 ].…”

“…SERS spectra of ( c ) 4-MBA molecules and ( d ) Sudan I molecules for different concentrations obtained with optimized xylan-capped Au/Ag nanoparticles of ( b ). All the figures are reprinted (adapted) with permission from [ 84 ], Copyright 2019 American Chemical Society.…”