Synthesis of vinyl-terminated Au nanoprisms and nanooctahedra mediated by 3-butenoic acid: direct Au@pNIPAM fabrication with improved SERS capabilities

Abstract

Here we describe the first seedless synthesis of vinyl-terminated Au nanotriangular prisms (AuNTPs) and nanooctahedra (AuNOC) in aqueous media. This synthesis is performed by chemical reduction of chloroauric acid (HAuCl4) with 3-butenoic acid (3BA) in the presence of benzyldimethylammonium chloride (BDAC). The principal novelties of the presented method are the use of a mixture of 3BA and BDAC, the synthesis of gold prisms and octahedra with controllable size, and the presence of terminal double bonds on the metal surface. Initially this method produces a mixture of triangular gold nanoprisms and octahedra; however, both morphologies are successfully separated by surfactant micelle induced depletion interaction, reaching percentages up to ∼90%. Moreover, the alkene moieties present on the gold surface are exploited for the fabrication of hybrid core@shell particles. Gold octahedra and triangular prisms are easily encapsulated by free radical polymerization of N-isopropylacrylamide (NIPAM). Finally, in order to obtain a gold core with the most number of tips, AuNTP@pNIPAM microgels were subjected to gold core overgrowth, thus resulting in star-shaped nanoparticles (AuSTs@pNIPAM). We use 4-amino-benzenethiol as the model analyte for SERS investigations. As expected, gold cores with tips and high curvature sites produced the highest plasmonic responses.

Biogenic Synthesis of Metal Nanoparticles Using a Biosurfactant Extracted from Corn and Their Antimicrobial Properties

“…In fact these components have been previously reported to act as reducing agents of different metal salts. For instance, unsaturated fatty acids have been recently used as the reducing agents to fabricate gold octahedral and triangular NPs [41,42,43]. Moreover, different proteins, such as human serum albumin (HSA), bovine serum albumin (BSA) or subtilisin Carlsberg (SC), have been also employed in the synthesis of gold NPs [44,45].…”

Plasmonics in Sensing: From Colorimetry to SERS Analytics

“…For this, the NP surface is first partially functionalized by a stabilizing ligand, followed by a codification with a SERS marker (Figure 7B), and the final overcoating with silica to create an inert outer surface layer [90]. Also, hyrogel shells have shown the potential for molecular trapping of analyte molecules [91,92]. The partial hydrophobic/hydrophilic nature of poly(N-isopropylacrylamide) during the reversible volume-phase transition can harvest analyte molecules from solution.…”

Use of capillary electrophoresis for characterisation of vinyl‐terminated Au nanoprisms and nanooctahedra

“…Before separation of synthesised AuNPs, and taking into account that there were no commercial standards available for their different morphologies, their absorption spectra were obtained after purification of the initial solution of gold nanoprisms and nanooctahedra. To do that, it was necessary to apply a surfactant micelle depletion‐induced flocculation by using CTAC as surfactant . Once AuNPs were synthesised, the dispersion was centrifuged at 7500 rpm during 30 min with the aim of removing the bigger particles obtained, then the precipitate was redispersed in CTAC.…”

“…Vinyl‐terminated AuNPs were synthetised using the following procedure based on the previously described by Casado‐Rodriguez et al . with modification in temperature and pH in the synthesis conditions in order to achieve better control in proportion of AuNTPs and AuNOs obtained in the final synthesis. In a typical synthesis, 50 mL of a mixture of 0.5 mM HAuCl 4 and 5 mM BDAC was introduced into a round bottom flask under mild magnetic stirring.…”

“…In the presented work, we have studied in a detailed way a seedless method that resulted in the synthesis of a mixture containing AuNTPs and AuNOs, which was recently reported by some of us . Consequently a better evaluation concerning the percentage of prisms and octahedra obtained by using a more appropriated technique is highly desired.…”