Bimetallic Gold Nanostars Having High Aspect Ratio Spikes for Sensitive Surface-Enhanced Raman Scattering Sensing

Abstract

There has been increasing interest in evolution of plasmonic nanoplatforms based on noble metal nanoparticles to achieve ultrasensitive detection of trace analyte molecules through solution-based surface-enhanced Raman spectroscopy (SERS). This work presents a surfactant-free synthesis method of bimetallic gold nanostars coated with silver (BGNS-Ag) having sharp, high aspect-ratio spikes for achieving ultrahigh detection sensitivity and high reproducibility. Specifically, the unique BGNS-Ag platform combines both the strong SERS enhancement effects of gold nanostar sharp spikes and the high scattering feature of the silver–gold bimetallic structure. To achieve SERS reproducibility, this solution-based SERS measurement requires minimal sample preparation without addition of any external reagents, which can cause irregular aggregation of nanoparticles and reduce the reproducibility of SERS measurements. Moreover, we have streamlined our SERS sensing procedure by using standard well-plates and a portable Raman device for SERS measurements, which could be utilized for rapid on-site detection. This solution-based SERS performance was studied using methylene blue (MB) as a model analyte system. The detection limit of MB was as low as 42 pM, indicating high sensitivity of detection using BGNS-Ag. To illustrate the usefulness for environmental sensing, we showed that the SERS sensor can detect a pesticide, thiram, at a concentration as low as 0.8 nM. This study demonstrated that the BGNS-Ag system could serve as an effective and versatile plasmonic-active platform for reproducible, fast, and in-field detection of small organic analytes at trace levels.

Sharp Branched Gold Nanostar-Based Lateral-Flow Immunoassay for Detection of Yersinia pestis

“…GNSPs and GNSs of three shape morphologies were prepared by using a surfactant-free seed-mediated synthesis method, where the GNSP was synthesized in the absence of Ag + , whereas the GNS synthesis was a Ag + -assisted growth method. , The three different nanostars were synthesized by varying Ag + concentrations from 20, 100, and 200 μM for GNS-1, GNS-2, and GNS-3, respectively. Figure a–e displays a representative 3D model and the STEM images of the GNSP and GNSs (GNS-1, GNS-2, and GNS-3).…”

“…As the GNS size is in the range of 100–200 nm, we believe that they can load a higher number of biomolecules than GNSPs. Second, GNSs exhibit strong localized surface plasmon resonance absorption which is important for achieving a strong optic absorption with extremely large molar extinction coefficients. − Third, GNSs have better flexibility for fine-tuning the size, shape, and tip morphology. − There have been reports on the anisotropic branched morphology of gold nanoparticle-based LFIA. For example, Zhang et al synthesized different sizes of gold nanoflowers and found that medium-sized gold nanoflowers show stronger optical sensitivity than conventional GNSPs .…”

Shape-Induced Variations in Aromatic Thiols Adsorption on Gold Nanoparticle: A Novel Method for Accurate Evaluation of Adsorbed Molecules

“…The number of molecules adsorbed on nanoparticle surfaces is usually estimated by evaluating the surface area of each particle and the particle concentration in the sample followed by assuming that analytes uniformly bind to the surface of the nanoparticles and form a complete-coverage monolayer. The surface area of the nanoparticles in most of the literature is estimated using data from transmission electron microscopy (TEM) or dynamic light scattering (DLS) (assuming spherical particles) while the concentration is theoretically calculated or measured (for example, by mass spectrometry). − In addition, the surface area of the analyte is estimated from its van der Waals radius and the assumption of a single-surface binding geometry. In the past few years some research articles have reported using NTA to determine both size and concentration of nanoparticles. − Some publications have attempted to get closer to the true surface area of nonspherical nanoparticles using the evaluation of the amount of alkanethiol adsorption from GC-MS data analysis .…”

A hybrid plasmonic nanoprobe using polyvinylpyrrolidone-capped bimetallic silver–gold nanostars for highly sensitive and reproducible solution-based SERS sensing

“…[27][28][29] Bimetallic Au-Ag nanostructure shows promising potential as a SERS sensor owing to their better chemical stability, flexibility for fine-tuning the size, and star shape of the Au nanoparticle core, and the high plasmonic effect of Ag. [30][31][32][33] Various synthesis strategies have been developed for bimetallic Au-Ag GNS fabrication. For example, Ma et al developed a core-shell Ag-Au GNS synthesis method which shows high SERS sensitivity than GNS.…”