Synthesis Of Gold Nanostars Research Articles

Giant Plasmonic Enhancement of Chiroptical Properties by Anisotropic Gold Nanocrystals Grown In Situ in a Chiral Polymer

AbstractPolymer‐based chiral materials with exceptional optical activity can dramatically impact integrated chiral photonics due to the tunability of their optical responses coupled with ease of fabrication. Realizing these applications requires increasing the absorbance dissymmetry factor. Here, in situ, the synthesis of gold nanostars is introduced in a chiral polymer medium to produce chiral polymer‐anisotropic plasmonic nanocrystal nanocomposites. The optimized nanocomposite shows a tenfold enhancement of dissymmetry factor, gabs (up to 0.64) and a corresponding 46‐fold augmented circular dichroism (CD) value upon annealing, relative to the annealed pure chiral polymer film. Moreover, the enhancement relative to the non‐annealed polymer‐gold nanostar nanocomposite is strikingly higher: a 35‐fold increase in gabs and a 4272‐fold increase in CD. Based on computational analysis, it is concluded that the local plasmon field enhancement around the crevices and tips of nanostars is mainly responsible for the observed effect which is further supported by a signal enhancement in Surface Enhanced Raman Scattering (SERS). Thus, this study underscores the significant role of close‐range plasmon interactions in altering the chiroptical response of nanocomposite materials and a practical pathway toward the realization of next‐generation integrated photonics and optoelectronic circuitry with photon spin control.

Impurities in polyvinylpyrrolidone: the key factor in the synthesis of gold nanostars.

Control over the synthesis of anisotropic nanoparticles is crucial as slight differences in their size, shape, sharpness, or the number of tips in the case of gold nanostars, has an inordinate influence on their properties and functionality for future applications. Herein, we show that the supplier and purity of polyvinylpyrrolidone (PVP) can significantly alter the synthesis of gold nanostars, demonstrating that impurities, not PVP itself, are the main factor responsible for star-like shape formation. We demonstrate that in the presence of pure PVP and N,N-dimethylformamide, the use of hydrazine leads to the formation of branched nanoparticles. This synthetic approach opens the door to solving issues associated with the use of commercial PVP during the synthesis of gold nanostars.

Synthesis of gold nanostars with fractal structure: application in surface-enhanced Raman scattering

Multi-branched gold nanostars with fractal feature were synthesized using the Triton X-100 participant seed-growth method. By increasing the amount of ascorbic acid, the branch length of gold nanostars could be greatly increased. It has been interesting to find that the secondary growth of new branches takes place from the elementary structure when the aspect ratio of the branches is greater than 8.0 and the corresponding plasmon absorption wavelength is greater than 900 nm. Raman activity of the gold nanostar films has been investigated by using the 4-mercaptobenzoic acid (4-MBA) as Raman active probe. Experimental results show that the surface-enhanced Raman scattering (SERS) ability of the gold nanostars could be efficiently improved when the fractal structure appears. The physical mechanism has been attributed to the intense increased secondary branch number and the increased “hot spots”. These unique multi-branched gold nanostars with fractal feature and great SERS activity should have great potential in sensing applications.

Optimizing gold nanostars as a colloid-based surface-enhanced Raman scattering (SERS) substrate

The one-pot seedless protocol provides a facile approach in the synthesis of gold nanostars (AuNS) that involves only three reagents, gold (III) chloride (HAuCl4), silver nitrate (AgNO3) and ascorbic acid (C6H8O6). While studies correlating the synthesis parameters of the seed-mediated protocol to surface-enhance Raman scattering (SERS) enhancement is well reported, the same understanding of the one-pot seedless protocol is limited. Here, we aim to elucidate how the synthesis parameters of AuNS from the one-pot seedless protocol, the AuNS concentration, surface passivation and aggregation level affect the colloidal SERS enhancement. Using crystal violet (CV) as a Raman probe molecule, we found that the SERS enhancement increases with Au3+/C6H8O6 molar ratio up to 0.60 and Au3+/Ag+ molar ratio up to 18. Although the surfactant, cetyltrimethylammonium bromide (CTAB) maintained colloidal stability, it reduced the SERS enhancement. Interestingly, the SERS enhancement did not increase monotonically with AuNS concentration, but decreased when AuNS concentration was beyond 15 pM. The SERS enhancement also increased with the increasing level of salt-induced aggregation of AuNS, but only within a few minutes. While the concept of SERS with colloidal nanostructures is not new, we have shown for the first time, a detailed systematic study of various parameters that affect the SERS enhancement of AuNS synthesized using a one-pot seedless protocol. This study enables us to optimize the SERS enhancement of AuNS at the synthesis level to make them effective colloid-based SERS substrates for potential use in intracellular biosensing.

Synthesis of gold nanostars with tunable morphology and their electrochemical application for hydrogen peroxide sensing

Gold nanostars (AuNSs) with tunable morphology were synthesized by a seed-mediated growth method using poly(diallyldimethylammonium chloride) (PDDA) as stabilizer. The number and length of the branches of the nanostars can be controlled by adjusting the amount of silver nitrate. In addition, the AuNSs exhibit an excellent catalytic effect toward the reduction of hydrogen peroxide (H2O2) in deoxygenated phosphate buffer (pH 7.0). Thus, the PDDA-protected AuNSs were utilized to modify glassy carbon electrode directly for fabricating non-enzymatic H2O2 sensor. The fast amperometric response, low detection limit, wide linear range, good selectivity and long-term stability for the electrochemical detection of H2O2 imply a good performance of the AuNSs based sensor.

A versatile, one-pot synthesis of gold nanostars with long, well-defined thorns using a lyotropic liquid crystal template

We describe a simple, one-pot, silver-assisted synthesis of branched gold nanoparticles (GNPs) (nanostars) using Ag NO3 and the mild reducing agent, ascorbic acid, in the presence of a lyotropic liquid crystal (LLC) template formed by Triton X-100 in water either in the hexagonal phase or the micellar phase above the critical micellar concentration. The LLC template is found to assist in the formation of well-defined nanostars with long, twinned thorns and provides the necessary colloidal stability that prevents the final nanostars from irreversible aggregation. In addition, the length of the thorns on the nanostars can be tailored by controlling the Au/Ag ratio in the growth solution. We discuss the contributions of the competing mechanisms that result in an optimal concentration of AgNO3 for the synthesis of nanostars with considerably longer thorns, which is only possible in the LLC template that slows down the growth of the thorns on the initially formed GNP seeds.

Abstract 1966: Plasmonic gold nanostars: A potential agent for molecular imaging and cancer therapy

Abstract Gold nanoparticles offer great potential for bioapplication due to their biocompatibility, chemical stability, and plasmon tunability. Due to the increased demand in custom-designed bioapplication, tailoring nanoparticle's plasmon for a specific application remains an active area of research. Plasmonic gold nanostars, with their sharp tips and small cores, yield unique optical properties in the near infrared region favorable for biological applications. We present a high-yield biocompatible synthesis of gold nanostars, whose geometry is adjustable such that the plasmon band can be tuned into the near-infrared “tissue diagnostic window”. Nanostars offer several interesting plasmon properties including intense surface-enhanced Raman scattering (SERS) for ultrasensitive detection, strong two-photon photoluminescence (TPL) for real-time particle tracking, and efficient photothermal transduction for hyperthermic therapy. Here, we demonstrate nanostars tracking and photothermal ablation both in vitro and in vivo. Using SKBR3 breast cancer cells incubated with bare nanostars, photothermal ablation was observed within 5 minutes of irradiation (980 nm CW laser, 15 W/cm2). On a mouse preinfused systemically with PEGylated nanostars for 2 days, extravasation of nanostars was observed and localized photothermal ablation was demonstrated on a dorsal window chamber within 10 minutes of irradiation (785 nm CW laser, 1.1 W/cm2). These preliminary results have illustrated the theranostic potential of gold nanostars for the use in molecular imaging and cancer therapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1966. doi:1538-7445.AM2012-1966