Biosynthesis of gold nanostructures has drawn increasing concerns because of its green and sustainable synthetic process. However, biosynthesis of gold nanoplates is still a challenge because of the expensive source and difficulties of controllable formation of morphology and size. Herein, one-pot biosynthesis of gold nanoplates is proposed, in which cheap yeast was extracted as a green precursor. The morphologies and sizes of the gold nanostructures can be controlled via varying the pH value of the biomedium. In acid condition, gold nanoplates with side length from 1300 ± 200 to 300 ± 100 nm and height from 18 to 15 nm were obtained by increasing the pH value. Whereas, in neutral or basic condition, only gold nanoflowers and nanoparticles were obtained. It was determined that organic molecules, such as succinic acid, lactic acid, malic acid, and glutathione, which are generated in metabolism process, played important role in the reduction of gold ions. Besides, it was found that the gold nanoplates exhibited plasmonic property with prominent dipole infrared resonance in near-infrared region, indicating their potential in surface plasmon-enhanced applications, such as bioimaging and photothermal therapy.

We demonstrate a CTAB-templated approach towards direct coating of mesoporous titania on gold nanorods in aqueous solutions. The formation of the mesoporous shell is found to be closely correlated with CTAB concentration and the amount of the titania precursor. This approach can be readily extended to form mesoporous titania shells on other CTAB-capped nanoparticles.

We report a facile and reproducible approach toward rapid seedless synthesis of single crystalline gold nanoplates with edge length on the order of microns. The reaction is carried out by reducing gold ions with ascorbic acid in the presence of cetyltrimethylammonium bromide (CTAB). Reaction temperature and molar ratio of CTAB/Au are critical for the formation of gold nanoplates in a high yield, which are, respectively, optimized to be 85 °C and 6. The highest yield that can be achieved is 60 % at the optimized condition. The synthesis to achieve the microscaled gold nanoplates can be finished in less than 1 h under proper reaction conditions. Therefore, the reported synthesis approach is a time- and cost-effective one. The gold nanoplates were further employed as the surface-enhanced Raman scattering substrates and investigated individually. Interestingly, only those adsorbed with gold nanoparticles exhibit pronounced Raman signals of probe molecules, where a maximum enhancement factor of 1.7 × 107 was obtained. The obtained Raman enhancement can be ascribed to the plasmon coupling between the gold nanoplate and the nanoparticle adsorbed onto it.

We developed a facile approach toward hybrid AgNP–graphene–AgNP sandwiched structures using self-organized monolayered AgNPs from wet chemical synthesis for the optimized enhancement of the Raman response of monolayer graphene. We demonstrate that the Raman scattering of graphene can be enhanced 530 fold in the hybrid structure. The Raman enhancement is sensitively dependent on the hybrid structure, incident angle, and excitation wavelength. A systematic simulation is performed, which well explains the enhancement mechanism. Our study indicates that the enhancement resulted from the plasmonic coupling between the AgNPs on the opposite sides of graphene. Our approach towards ideal substrates offers great potential to produce a “hot surface” for enhancing the Raman response of two-dimensional materials.

In recent years hydrogen peroxide has often been used as the oxidizing agent to tune the resonance wavelength of gold nanorods (AuNRs) through anisotropic shortening in the presence of cetyltrimethylammonium bromide (CTAB). However, a complete picture of the reaction mechanism remains elusive. In this work, we present a systematic study on the mechanism of the AuNR oxidation by revealing the important role of bromide. Hydrogen peroxide slowly oxidizes bromide into elemental bromine. The latter two form tribromide, which exhibits a characteristic 272 nm absorption peak. The peak intensity, representing the concentration of tribromide, is found to have a linear correlation with the oxidation rate of AuNRs. Tribromide approaches AuNRs through conjugating strongly with CTA cationic micelles, which leads to the oxidation occurring on the surface of AuNRs. In contrast, the CTA micelles protect AuNRs from the direct oxidation by hydrogen peroxide. Our findings are believed to provide new insights into the reaction mechanism occurring in the relevant CTAB–AuNR systems, which can be important for understanding the principles governing the reaction dynamics.

Asymmetric three-dimensional (3D) nanoarchitectures that cannot coincide with their mirrored-symmetric counterparts are known as chiral objects. Numerous studies have focused on chiral plasmonic nanoarchitectures created intentionally with 3D asymmetric configurations, whose plasmonic chirality is promising for various nanoplasmonic and nanophotonic applications. Here, we show that gold nanorod (AuNR) plasmonic nanoarchitectures assembled on a soft 2D DNA origami template, which was often simplified to be a rigid rectangle, can exhibit strong chiroptical activities. The slight flexibility of the origami templates was found to play a critical role in inducing the plasmonic chirality of the assembled nanoarchitectures. Our study set a new example of reflecting the native conformation of nanostructures using chiral spectroscopy and can inspire the exploration of the softness of DNA templates for the future design of assembled chiral nanoarchitectures.

Circular dichroism (CD) studies on single nanostructures can yield novel insights into chiroptical physics that are not available from traditional ensemble-based measurements, yet they are challenging because of their weak signals. By introducing an oblique excitation beam, we demonstrate the observation and spectroscopic analysis of a prominent plasmonic chiroptical response from a single v-shaped gold nanorod dimer nanostructure. We show that circular differential scattering from the obliquely excited gold nanorod dimer yields a characteristic bisignate peak-dip spectral shape at hybridized energies of the dimer. This chiroptical response can be ascribed to extrinsic chirality which depends on the geometry configurations of the chiral arrangement. Due to strong near-field coupling, the dipole orientations of the hybridized resonance modes can be in favor of the incident circularly polarized light where a maximum g-factor of ∼0.4 is observed. Promising applications of this chiroptical arrangement as a key component can be in electronics, photonics, or metamaterials.

Discrete, three-dimensional (3D) gold nanoparticle (AuNP) tetrahedron nanoarchitectures are successfully self-assembled with DNA origami as template with high purity (>85%). A distinct plasmonic chiral response is experimentally observed from the AuNP tetrahedron nanoarchitectures and appears in a configuration-dependent manner. The chiral optical properties are then rationally engineered by modifying the structural parameters including the AuNP size and interparticle distance. Theoretical study of the AuNP tetrahedron nanoarchitectures shows the dependence of the chiral optical property on the AuNP size and interparticle distance, consistent with the ensemble averaged measurements.Keywords: chiral optical property; DNA self-assembly; gold nanoparticle; tetrahedron nanostructure;

Through wet-chemical assembly methods, gold nanorods were placed close to each other and formed a dimer with a gap distance ~1 nm, and hence degenerated plasmonic dipole modes of individual nanorods coupled together to produce hybridized bonding and antibonding resonance modes. Previous studies using a condenser for illumination result in averaged signals over all excitation angles. By exciting an individual dimer obliquely at different angles, we demonstrate that these two new resonance modes are highly tunable and sensitive to the angle between the excitation polarization and the dimer orientation, which follows cos2φ dependence. Moreover, for dimer structures with various structure angles, the resonance wavelengths as well as the refractive index sensitivities were found independent of the structure angle. Calculated angle-resolved plasmonic properties are in good agreement with the measurements. The assembled nanostructures investigated here are important for fundamental researches as well as potential applications when they are used as building blocks in plasmon-based optical and optoelectronic devices.

Gold nanodimers (GNDs) are assembled with high uniformity as ideal surface-enhanced Raman scattering (SERS) substrates through DNA-directed self-assembly of gold nanoparticles. The interparticle distance within GNDs is precisely tailored on the order of a few nanometers with changing the molecule length of DNA bridge. The ensemble SERS activity of monodispersed GNDs is then rationally engineered by modifying the structural parameters of GNDs including the particle size and interparticle distance. Theoretical studies on the level of single GND evidence the particle size- and interparticle-distance-dependent SERS effects, consistent with the ensemble averaged measurements.Keywords: DNA self-assembly; gold nanoparticle; nanostructure; surface-enhanced Raman scattering;