Morphologies and surface plasmon resonance properties of monodisperse bumpy gold nanoparticles

The influence of the morphology of gold nanoparticles on the surface plasmon resonance was investigated experimentally and theoretically. Highly monodisperse bumpy gold nanoparticles of increasing size were synthesized, and the surface plasmon resonance wavelength shifted to longer wavelengths more rapidly with increasing particle size for bumpy particles than for spherical gold nanoparticles. The detailed surface morphology of bumpy gold nanoparticles was characterized by AFM, TEM, and SEM, and the optical properties were investigated on a single particle level. The comparison of the plasmon resonant properties between bumpy and spherical gold nanoparticles was also examined with a theoretical model.     

A surface plasmon resonance study on the optical properties of gold nanoparticles on thin gold films

We report on an investigation of the optical properties of gold nanoparticles assembled as thin films of different thickness. The nanoparticles were linked to the surface of a gold chip by dithiol reagents and studied by surface plasmon resonance (SPR) spectroscopy and atomic force microscopy. There is good correlation between the experimental findings and theoretical simulation, and the respective data reveal the presence of ordered nanostructures in the assemblies. The shift in the SPR angle is linearly dependent on the particle size and the ratio of the different particles. SPR spectroscopy also reveals important information in terms of the optical constants of such films. This shall be further applied to in-situ quality control in the fabrication of optoelectronic, solar cell and semiconductor devices.

Controlled interparticle spacing for surface-modified gold nanoparticle aggregates

Aggregation of gold nanoparticles of increasing size has been studied as a consequence of adsorption of 2-aminothiophenol (ATP) on gold nanoparticle surfaces. The capping property of ATP in the acidic pH range has been accounted from UV-vis absorption spectroscopy and surface-enhanced Raman scattering (SERS) studies. The effect of nanoparticle size (8-55 nm) on the nature of aggregation as well as the variation in the optical response due to variable degree of interparticle coupling effects among the gold particles have been critically examined. Various techniques such as transmission electron microscopy, X-ray diffraction, zeta-potential, and average particle size measurement were undertaken to characterize the nanoparticle aggregates. The aggregate size, interparticle distances, and absorption band wavelengths were found to be highly dependent on the pH of the medium and the concentration of the capping agent, ATP. The acquired SERS spectra of ATP relate the interparticle spacing. It has been observed that the SERS signal intensities are different for different sized gold nanoparticles.     

Green preparation of hollow mesoporous silica nanosphere inside-loaded gold nanoparticles and the catalytic activity

In this work, an active nano-catalyst with gold nanoparticles loaded in hollow mesoporous silica nanospheres (HMSNs/Au) was prepared by a one-pot sol-gel method, in which gold ions were loaded in hollow mesoporous silica spheres followed by sodium alginate reduction. The characterization of the HMSNs/Au were determined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), N₂ adsorption–desorption isotherms (BET). The high catalytic activity of HMSNs/Au, denoted as apparent turn-over frequency (TOF), was detected by UV-Vis spectrophotometer for the catalytic reduction of 4-nitrophenol (74.5 h^?1) and 2-nitrophenol (108.7 h^?1) in the presence of sodium borohydride solution due to the small gold nanoparticles size and overall exposure of active sites. It is expected that this ecofriendly approach to prepare inorganic composited nanoparticles as high active catalysts based on hollow mesoporous materials was a promising platform for loading noble metal nanoparticles.     

Monitoring gold nanorod synthesis by localized surface plasmon resonance

Surfactants can direct the growth of gold nanoparticles to create anisotropic structures in high yield by simple means, yet the exact roles of surfactants and other reactants are not entirely understood. Here we show that one can exploit the geometrical dependence of the localized surface plasmon resonant extinction spectrum of gold nanorods to monitor their synthesis kinetics. By using quantitative measurements of nanorod extinction cross sections, Gans' theory for the spectral extinction of prolate spheroids can be normalized to provide values for the nanorod length and diameter from extinction spectra measured during growth. The nanorod length growth rate was first observed at 0.15 nm/s and decayed during the growth reaction. The rate dependence on nanorod size did not correspond to any simple reaction-limited or diffusion-limited growth mechanisms.     

Construction of simple gold nanoparticle aggregates with controlled plasmon–plasmon interactions

We have developed a colloidal assembly for the study of plasmon–plasmon interactions between gold nanoparticles. Colloidal aggregates of controlled size and interparticle spacing were synthesized on silica nanoparticle substrates. Following the immobilization of isolated gold nanoparticles onto silica nanoparticles, the surfaces of the adsorbed gold nanoparticles were functionalized with 4-aminobenzenethiol. This molecular linker attached additional gold nanoparticles to the ‘parent' gold nanoparticle, forming small nanoparticle aggregates. The optical absorption spectrum of these clusters differed from that of gold colloid in a manner consistent with plasmon–plasmon interactions between the gold nanoparticles.     

Non-linear plasmon response to protein binding at a nanostructured gold particle plasmon resonance surface

Rapid adsorption kinetics have been observed for protein binding to a 800 nm aggregated nanoparticle, showing extreme sensitivity resulting from a non-linear particle plasmon response.     

Preparation of silica-encapsulated hollow gold nanosphere tags using layer-by-layer method for multiplex surface-enhanced raman scattering detection

The use of silica shells offers many advantages in surface-enhanced Raman scattering (SERS)-based biological sensing applications due to their optical transparency, remarkable stability in environmental media, and improved biocompatibility. Here, we report a novel layer-by-layer method for the preparation of silica-hollow gold nanosphere (HGN) SERS tags. Poly(acrylic acid) was used to stabilize Raman reporter-tagged HGNs prior to the adsorption of a coupling agent, after which a silica shell was deposited onto the particle surface using Sto?ber's method. Importantly, competitive adsorption of the Raman reporter molecules and coupling agents, which results in unbalanced loading of reporter molecules on individual nanoparticles, was avoided using this method. As a result, the loading density of reporter molecules could be maximized. In addition, HGNs exhibited strong enhancement effects from the individual particles because of their ability to localize the surface electromagnetic fields through pinholes in the hollow particle structures. The proposed layer-by-layer silica-encapsulated HGN tags showed strong SERS signals as well as excellent multiplexing capabilities.     

Detection of ozone gas using gold nanoislands and surface plasmon resonance

Gold nanoislands interact with gaseous ozone to produce a surface plasmon resonance shift, similarly to the interaction of ozone and gold nanoparticles in water. Gold nanoislands are produced by sputtering, which significantly simplifies the synthesis and produces controlled size for the gold nanoislands. The shift of surface plasmon resonance peak was monitored while gold nanoislands were exposed to variable concentration of gaseous ozone. The shift was then correlated with ozone concentration. Our current results indicate sensing gaseous ozone at concentration of as low as 20 μg/L is achievable. Gold nanoislands were reversed to their original wavelength and were able to cycle between the wavelengths as ozone was introduced and removed. Potentially, this system can be useful as a sensor that identifies the presence of ozone at low part-per-billion concentrations of ozone in gaseous media.     

Waveguide surface plasmon resonance studies of surface reactions on gold electrodes

We describe the fabrication and characterisation of gold-coated graded index channel waveguide sensors designed for simultaneous electrochemical and surface plasmon resonance studies. The active sensing electrode area is a thin gold film between 0.5 and 5 mm in length and 200 microm wide deposited on top of a 3 microm wide waveguide which forms one arm of a Y-junction while the other arm of the Y-junction serves as a reference. Using these devices we have measured simultaneously the changes in transmittance through the device whilst carrying out cyclic voltammetry in either sulfuric or perchloric acid solution or during the deposition of an UPD layer of copper at the gold surface. In all cases we obtain stable and reproducible results which demonstrate the very high sensitivity of the devices to sub-monolayer changes occurring at the gold electrode surface. The response of these integrated optoelectrochemical devices is discussed in terms of a numerical model for the propagation of light within the waveguide structure.     

Gold hollow nanospheres: tunable surface plasmon resonance controlled by interior-cavity sizes

Uniform gold hollow nanospheres with tunable interior-cavity sizes were fabricated by using Co nanoparticles as sacrificial templates and varying the stoichiometric ratio of starting material HAuCl4 over the reductants. The formation of these hollow nanostructures is attributed to two subsequent reduction reactions: the initial reduction of HAuCl4 by Co nanoparticles, followed by the reduction by NaBH4. In addition, a thick layer of silica was successfully coated onto the gold hollow nanospheres. These nanostructures are extensively characterized by TEM, XRD, HRTEM, SEM, electron diffraction, energy-dispersive X-ray analysis, and UV-visible absorption spectroscopy. It is evident that the SPR peak locations corresponding to these hollow nanospheres are shifted over a region of more than 100 nm wavelength due to changes of shell thickness, which make these optically active nanostructures of great interest in both fundamental research and practical applications.     

银薄层控制金纳米四足体的重塑和等离激元调谐

探究了溶液中不同温度以及不同溶液成分（I^-的引入）对金纳米四足体（GNTPs）重塑过程的影响,表明了GNTPs的重塑机制为Ostwald熟化,即弱结合的表面Au原子在高凸曲率区域溶解和在凹区域重新沉积。这种重塑过程可以随时通过镀银薄层在几秒内阻止,GNTPs的形貌可以在最大程度上得到很好的稳定,从而也可以防止其光学性质的演变。在此基础上,通过紫外可见近红外（UV-Vis-NIR）吸收光谱和基于同步辐射的小角X射线散射（SAXS）进一步研究了GNTPs/Ag的稳定性,并通过表面增强拉曼散射（SERS）光谱证实了GNTPs/Ag的光学响应。     

Synthesis temperature as an instrument for tuning the plasmon resonance of gold nanorods

The one-stage unseeded method of the synthesis of gold nanorods has been employed to systematically study the influence of process temperature on nanorods sizes and plasmon resonance properties. It has been shown for the first time that even slight variations in the temperature have a very strong effect on these characteristics. Analysis of the obtained results has indicated that the observed effect is caused by the influence of temperature on the nucleation rate of the nanoparticles.     

Measuring the number concentration of arbitrarily-shaped gold nanoparticles with surface plasmon resonance microscopy

Molar concentration of gold nanoparticles is one of the most critical parameters of gold colloids in order to develop their applications in sensing, diagnostics and nanomedicine. Previous methods often stand just for gold nanoparticles with regular shape and narrow size distribution. In the present work, we proposed an absolute quantification method that determined the molar concentration of gold nanoparticles with arbitrary shapes and polydisperse sizes. This approach involved the real time monitoring and counting of individual nanoparticles collision events, from which the quantification of molar concentration was achieved using a theoretical model consisting of Fick’s laws of diffusion and Stokes-Einstein equation. The determination of spherical gold nanoparticles concentration resulted in excellent agreement with traditional spectrometry method. It was further demonstrated that the present approach can be expanded to determine the molar concentration of gold nanoparticles with arbitrary shapes and poly-diversed distributions.     

银薄层控制金纳米四足体的重塑和等离激元调谐

探究了溶液中不同温度以及不同溶液成分(I^-的引入)对金纳米四足体(GNTPs)重塑过程的影响,表明了GNTPs的重塑机制为Ostwald熟化,即弱结合的表面Au原子在高凸曲率区域溶解和在凹区域重新沉积。这种重塑过程可以随时通过镀银薄层在几秒内阻止,GNTPs的形貌可以在最大程度上得到很好的稳定,从而也可以防止其光学性质的演变。在此基础上,通过紫外可见近红外(UV-Vis-NIR)吸收光谱和基于同步辐射的小角X射线散射(SAXS)进一步研究了GNTPs/Ag的稳定性,并通过表面增强拉曼散射(SERS)光谱证实了GNTPs/Ag的光学响应。     

Surface plasmon resonance

During last decade there has been significant progress in the development of analytical techniques for evaluation of receptor-ligand iteraction. Surface plasmon resonance (SPR)-based optical biosensors are now being used extensively to defined the kinetics of wide variety of macromolecular interactions and high- and low-affinity small molecule interactions. The experimental design data analysis methods are evolving along with widespread applications in ligand fishing, microbiology, virology, host-pathogen interaction, epitope mapping and protein-, cell-, membrane-, nucleic acid-protein interactions. SPR based biosensors have strong impact on basic and applied research significantly. This brief review describes the SPR technology and few of its applications in relation to receptor-ligand interaction that has brought significant change in the methodology, analysis, interpretation, and application of the SPR technology.     

Photochemical and analytical applications of gold nanoparticles and nanorods utilizing surface plasmon resonance

In recent years, plasmonics has emerged as a promising tool in the fields of analytical chemistry and biochemistry. In particular, surface plasmon resonance at the surfaces of gold nanostructures has led to the development of widespread interest in gold nanoparticles. In this review, we describe some of the recent progress in the manufacture and use of gold nanoparticles, with particular emphasis on gold nanorods. Furthermore, the spectroscopic and photochemical applications of gold nanospheres and nanorods are described.     

Janus particles with a functional gold surface for control of surface plasmon resonance

We report in this study the presence of Janus particles, which are candidates for use with electronic color papers. We used negatively charged polystyrene particles (370 nm) as the core particles, and gold was then sputtered onto their packed monolayer under several conditions. The sputtered particles were next redispersed into the aqueous medium by gentle sonication. Gold nanoparticles localized on one side of the cores could also serve as seeds for subsequent shell growth by electroless gold plating. Through these treatments, a series of well-dispersed Janus particles were obtained with gold nanostructures of different size and shape only on one side. Their dispersions showed different colors originating from the surface plasmon resonance absorption of gold nanoparticles localized on the hemisphere. The particles obtained by this approach have potential applications such as in sensors and electronic color paper.