Oil-Free Gold Nanobipyramid@Ag Microgels as a Functional SERS Substrate for Direct Detection of Small Molecules in a Complex Sample Matrix

Abstract

Surface-enhanced Raman scattering (SERS) is a supersensitive analysis technology based on the target molecular fingerprint information. The enhancement of local electromagnetic field of the SERS substrate would increase the target molecules' Raman intensity which adsorb on the surface of nanoparticles. However, the existing adhesive macromolecules in the complex mixed sample would interfere with the adsorption of small target molecules, and it weakens the Raman intensity of target molecules. Microgels are one of the potential materials to suppress the interference of adhesive macromolecules and to avoid the complex pretreatments. However, most of the current microgel synthesis methods involve complex operations with precise instrumentation or the interference of oil and organic reagents. In this work, a simple and oil-free method was proposed to synthesize the gold nanobipyramid (Au NBP) @Ag@hyaluronic acid microgel via the condensation reaction of carboxyl and amino groups. As a proof-of-concept demonstration for small-molecule detection, the rhodamine 6G (R6G) molecules were allowed to enter inside the microgel through the meshes and adsorb on the surface of Au NBP@Ag nanoparticles within 30 min, while the macromolecule (bovine serum albumin in this case) was retained outside the microgel in the meantime. In addition, under the combined action of lightning rod effect of Au NBP and surface plasmon resonance effect of silver render the microgels with high SERS activity. The synthetic Au NBP@Ag@hyaluronic acid microgels were applied to detect 6-thioguanine in the human serum without any pretreatment process, and it showed a high signal enhancement and stable SERS signal, which can satisfy the requirement of clinical diagnosis. These results show that the proposed microgels have potential applications in the field of point-of-care testing.

Gold Nanobipyramid Hotspot Aggregation-Induced Surface-Enhanced Raman Scattering for the Ultrasensitive Detection of miRNA

“…Relying on the local surface plasmon resonance (LSPR) properties, , noble metal nanoparticles can generate a strong local electric field under laser irradiation, especially at the vertices, tips, and gaps where the electric field is much stronger than the external electric field, which is called “hotspots”, and the Raman molecules adsorbed at the hotspots can generate stronger SERS signals. − Compared with other plasma nanoparticles such as gold nanospheres (Au NPs) and gold nanorods (Au NRs), gold nanobipyramids (Au NBPs) can produce stronger electromagnetic enhancement effects due to the advantages of large surface roughness and sharp tips, , which were used to construct the SERS biosensor. However, the number of Raman molecules could not be adsorbed at the tip where the hotspot effect is strongest, and the disordered distribution of plasma nanoparticles leads to a low hotspot effect, which ultimately limited Raman enhancement. − In this work, Au NBPs were assembled on the four vertexes of tetrahedral DNA nanostructures (TDNs) to achieve the ordered aggregation of hotspots for increasing the hotspot effect, and the number of Raman molecules methylene blue (MB) could be immobilized near the tip of Au NBPs to significantly enhance the SERS signal for the sensitive detection of miRNA.…”

High‐Performance Hydrogel SERS Chips with Tunable Localized Surface Plasmon Resonance for Coordinated Electromagnetic Enhancement with Chemical Enhancement

“…It is well known that hydrogels have a porous network structure of finite size, allowing the entry of molecules with a hydrodynamic diameter smaller than the pore size. [39] Thus, the three SERS chips are soaked in the test solutions to enrich the target molecules. The effect of soaking time on the SERS intensities of amoxicillin, pymetrozine and chlorpyrifos on the corresponding SERS chip is investigated (Figure S13, Supporting Information).…”

Advances in surface‐enhanced Raman spectroscopy technology for detection of foodborne pathogens

“…The rod‐shaped nanosol substrates are generally obtained by seed‐mediated methods. It was found that the plasmon resonance ranges of nanorods with different aspect ratios are different, and their SERS activities were also significantly different (Lin et al., 2021). The plasmon wavelength of nanorods was adjusted by appropriate size so that it was close to the absorption and excitation line of the target to obtain the maximum enhancement factor (Sha et al., 2021).…”