Binary Thiol-Capped Gold Nanoparticle Monolayer Films for Quantitative Surface-Enhanced Raman Scattering Analysis

Abstract

Surface-enhanced Raman scattering (SERS) can provide fingerprint information of analyte molecules with unparalleled sensitivity. However, quantitative analysis using SERS has remained one of the major challenges owing to the difficulty of obtaining reproducible SERS substrates with high-density hotspots. Here, we report the rational design and fabrication of a binary thiol-capped gold nanoparticle (AuNP) monolayer film (MLF) as a substrate for highly sensitive and quantitative SERS analysis. The two thiol ligands chemically bonded to the AuNPs play different roles: dodecanethiol with a long alkyl chain controls the interparticle gaps and electromagnetic coupling among AuNPs and 4-mercaptopyridine works as a Raman internal standard (IS). The binary thiol-capped AuNPs can self-assemble into an ordered MLF with high-density hotspots and uniformly distributed IS. The asprepared MLF has been demonstrated as a reliable SERS substrate for quantitative detection of fungicide malachite green in aqueous solution, with a high enhancement factor (up to 3.3 × 10 7 ) and a low detection limit (100 pM). Moreover, the MLF SERS substrate is flexible and transparent, which has enabled in situ detection of trace fungicide residues in a shrimp tissue.

Self-assembly of colloidal nanoparticles into 2D arrays at water–oil interfaces: rational construction of stable SERS substrates with accessible enhancing surfaces and tailored plasmonic response

“…Nonetheless, this work pioneered the use of charge-neutral thiols as organic modifiers to produce noble metal nanoparticle arrays at wateroil interfaces, which remains a widely employed approach. [37][38][39] In principle, it should be possible to remove charged surface ligands to reduce electrostatic repulsion between Ag/Au nanoparticles with any type of charge-neutral thiol modifier. However, in practice it has been found that the molecular structure of the modifier is very important and that the use of small molecules, which are unable to provide sufficient interparticle steric repulsion as modifiers, typically leads to uncontrolled aggregation of the nanoparticles, resulting in the formation of arrays with numerous defects, which is undesirable for SERS measurements.…”

“…2d). [39] Within this system the bulky dodecanthiols acts as a spacer to prevent aggregation of the nanoparticles while the 4mercaptopyridine acts as an internal standard for quantitative SERS measurements. Although using modifiers to remove surface-charge is an efficient method to fabricate densely packed 2D arrays of plasmonic nanoparticles which exhibit strong plasmonic properties, one major drawback with this approach is that the modifier molecules will inevitably compete with analyte molecules for the enhancing surface, which is particularly undesirable for SERS studies of analytes at low concentrations and/or with weak affinity for the enhancing surface.…”

“…As shown in Figure 5a, the most widely reported examples of these combined approaches are those where cosolvents/aqueous salts were used to reduce surface-charge to induce self-assembly while modifiers were used to prevent aggregation of the nanoparticles. [39,[50][51][52][53] The combined use of promoters and modifiers for producing plasmonic interfacial nanoparticle arrays for SERS has also been demonstrated. [53,[59][60] As shown in Figure 5b, He et al found that the use of tetramethylammonium (TMA + ) promoters or 1dodecane thiol (DDT) modifiers alone led to the formation of sparse and aggregated 2D arrays of Au nanoparticles, respectively, and that optimal results were achieved when the modifier and promoter were used in combination.…”

The rationality of using core–shell nanoparticles with embedded internal standards for SERS quantitative analysis based glycerol-assisted 3D hotspots platform

“…MG is a common antibiotic which has been widely used in the pharmaceutical and aquaculture industries as it is effective at the prevention and treatment of fungal and parasitic infections in aquacultures. 46,47 However, MG has high toxicity, high residue, and carcinogenic, teratogenic and mutagenic side effects. 48 Therefore, many countries have listed MG as a banned drug in aquaculture.…”

3D Hotspot Matrix of Au Nanoparticles on Au Nanostructures with a Spacer Layer of Dithiol Molecules for Highly Sensitive Surface-Enhanced Raman Spectroscopy

“…3D nanostructures created by molecule-based self-assembly have fascinated attention towards highly sensitive SERS platforms due to their cost-effective fabrication and ease of precise control of nanogap [22][23][24][25][26][27] . A variety of molecules have been utilized to assemble nanoparticles (NPs) into 3D con gurations.…”