Synthesis of uniform gold nanoparticles using non-pathogenic bio-control agent: evolution of morphology from nano-spheres to triangular nanoprisms

Green synthesis of gold nanospheres with uniform diameter and triangular nanoprisms with optically flat surface was carried out using a non-pathogenic bio-control agent Trichoderma asperellum for reduction of HAuCl(4). Kinetics of the reaction was monitored by UV-Vis absorption spectroscopy. No additional capping/complexing agent was used for stabilizing the gold nanoparticles. Evolution of morphology from pseudospherical nanoparticles to triangular nanoprisms was studied by transmission electron microscopy (TEM). It revealed that three or more pseudospheres fused to form nanoprisms of different shapes and sizes. Slow rate of reduction of HAuCl(4) by constituents of cell-free fungal extract was instrumental in producing such exotic morphologies. Isolation of gold nanotriangles from the reacting masses was achieved by differential centrifugation.     

Time‐Dependent Surface Plasmon Resonance Spectroscopy of Silver Nanoprisms in the Presence of Halide Ions

Herein, we find that the surface plasmon resonance (SPR) spectra of silver nanoprisms in the presence of halide ions change gradually with reaction time. The changes in the spectra correspond to the shape transformation of silver nanoprisms. There are threshold concentrations of halide ions that initiate the shape‐transformation reaction. The threshold concentrations for Cl^?, Br^?, and I^? are about 3×10^?4 M , 1×10^?6 M , and 1.5×10^?6 M , respectively. Any concentrations of the added halide ions above these thresholds can eventually etch the silver nanoprisms into nanodisks if the reaction time is long enough. The higher the concentration of the halide ions, the higher the etching rate will be. The kinetics of the shape transformation of the silver nanoprisms can be studied by recording their time‐dependent surface plasmon resonance (SPR) spectra on a commercial UV/Vis–NIR spectrometer. The peak positions of in‐plane dipole SPR bands of silver colloids in the presence of chloride and bromide ions can be fitted very well with the biexponential functions. We propose that the fast components of the biexponential behaviors should correlate to the truncating effect on the corners of silver nanoprisms, and the slow component should correlate to the redeposition of the truncated residues onto the basal plane of the nanoplates.     

Colorimetric Determination Of Hydrogen Peroxide Based on Localized Surface Plasmon Resonance of Silver Nanoprisms Using a Microchannel Chip

Silver nanoprisms (AgNPrs) have unique optical phenomena due to their localized surface plasmon resonance that results in the extinction of light from the visible to the near-infrared spectral region. In this study, we propose the colorimetric determination of silver nanoprisms in microchannels using a smartphone camera. Image acquisition was performed by capturing an image of the colloidal solution of the silver nanoprisms in the microchannel using the transmitted light. Red, green, and blue chromaticity levels were extracted from the recorded images for further quantification of the silver nanoprisms. This technique was employed for the detection and colorimetric determination of hydrogen peroxide (H₂O₂). Good linearity between the change in the green chromaticity level and concentration of hydrogen peroxide was observed for values from 10 to 300?μM with an R² value of 0.9670. We anticipate that the developed methodology for the quantification of silver nanoprisms and hydrogen peroxide by monitoring the change in color in the images of transmitted light will enhance the development of simple, rapid, and reliable detection systems for quality control in the production of silver nanoprisms as well as in chemical sensor applications.     

Selectively colorimetric detection of cysteine with triangular silver nanoprisms

Triangular silver nanoprisms were prepared and applied to make colorimetric detection of cysteine based on our findings that cysteine could lead to the blue shift of the dipole plasmon resonance absorption,but other 19 kinds of natural amino acids could not.Cysteine with a concentration 160 nmol/L can result in a color change that can be discerned with naked eyes.     

Multipole plasmon resonances in gold nanorods

The optical properties of gold rods electrochemically deposited in anodic aluminum oxide templates have been investigated. Homogeneous suspensions of rods with an average diameter of 85 nm and varying lengths of 96, 186, 321, 465, 495, 578, 641, 735, and 1175 nm were fabricated. The purity and dimensions of these rod nanostructures allowed us to observe higher-order multipole resonances for the first time in a colloidal suspension. The experimental optical spectra agree with discrete dipole approximation calculations that have been modeled from the dimensions of the gold nanorods.     

Growth mechanism and optical properties of aligned hexagonal ZnO nanoprisms synthesized by noncatalytic thermal evaporation

Vertically aligned perfectly hexagonal-shaped ZnO nanoprisms have been grown on a Si(100) substrate via a noncatalytic thermal evaporation process by using metallic zinc powder in the presence of oxygen gas. The as-grown nanoprisms consist of ultra smooth Zn-terminated (0001) facets bounded with the {0110} surfaces. The as-synthesized products are single-crystalline with the wurtzite hexagonal phase and grown along the [0001] direction, as confirmed from the detailed structural investigations. The presence of a sharp and strong nonpolar optical phonon high-E2 mode at 437 cm(-1) in the Raman scattering spectrum further confirms good crystallinity and wurtzite hexagonal phase for the as-grown products. The as-grown nanoprisms exhibit a strong near-band-edge emission with a very weak deep-level emission in the room-temperature and low-temperature photoluminescence measurements, confirming good optical properties for the deposited products. Moreover, systematic time-dependent experiments were also performed to determine the growth process of the grown vertically aligned nanoprisms.     

Ultrasonically induced Au nanoprisms and their size manipulation based on aging

A simple sonochemical approach was developed for the synthesis of single-crystal Au nanoprisms with triangular or hexagonal shape, 30-40 nm planar dimension, and 6-10 nm thickness in an ethylene glycol solution. It has been shown that ethylene glycol, the surfactant poly(vinylpyrrolidone), and ultrasonic irradiation play important roles in the formation of Au nanoprisms. The subsequent aging induces the growth of Au nanoprisms, which is attributed to the existence of residual reduced Au degrees atoms and Au clusters in the solution. Further growth of Au nanoprisms could be realized by adding a given amount of HAuCl4 to the irradiated and aged Au nanodisk colloidal solution, which provides a simple and an effective method to synthesize Au nanoprisms with different sizes. Au nanoprisms with planar sizes from 70 to 400 nm have been successfully synthesized based on this strategy.     

Some Aspects of Seedless Synthesis of Gold Nanorods

Seedless synthesis of gold nanorods with the use of sodium borohydride and hydroquinone as reductants of metal ions has been systematically studied. The effect of reaction system composition on the morphology and optical characteristics of the formed particles has been determined. It has been found that the position of the band of the longitudinal surface plasmon resonance of the nanorods varies nonmonotonically with variations in the concentration of hydroquinone or silver nitrate. The seedless synthesis has been shown to yield high-quality gold nanorods, with the tunable position of their longitudinal surface plasmon resonance in a wide spectral range (from 700 to ~1050 nm). Therewith, the conversion of metal ions is no lower than 78 wt %.     

Discovery of the DNA "genetic code" for abiological gold nanoparticle morphologies

DNA is in control: Different combinations of DNA nucleotides can control the shape and surface roughness of gold nanoparticles during their synthesis. These nanoparticles were synthesized in the presence of either homogenous oligonucleotides or mixed-base oligonucleotides using gold nanoprisms as seeds. The effect of the individual DNA bases and their combinations on shape control are shown in the figure.     

银纳米棱镜的形成及其光学性能研究

以有机溶剂作为反应介质,聚合物为稳定剂,通过微波辅助溶液法成功地制备了具有特殊光学性能的银纳米棱镜.利用X射线衍射、透射电子显微镜和紫外-可见光谱等手段跟踪反应过程.结果显示,随着反应的进行,银纳米粒子由10nm左右的球形颗粒逐渐转变为具有规则三角形(或缺角的三角形)形貌的纳米棱镜;同时,紫外-可见吸收峰不但显示出明显的量子尺寸效应,而且吸收峰也由单一的等离子共振吸收峰变为多重的多极吸收峰共同存在,胶体溶液也随之显示出不同的颜色.改变反应物的配比、体系的浓度及无机前驱物都会得到位置和峰形各不相同的吸收曲线,从而得到多彩的纳米银胶体溶液.     

Plasmon coupling in nanorod assemblies: optical absorption, discrete dipole approximation simulation, and exciton-coupling model

The shape anisotropy of nanorods gives rise to two distinct orientational modes by which nanorods can be assembled, i.e., end-to-end and side-by-side, analogous to the well-known H and J aggregation in organic chromophores. Optical absorption spectra of gold nanorods have earlier been observed to show a red-shift of the longitudinal plasmon band for the end-to-end linkage of nanorods, resulting from the plasmon coupling between neighboring nanoparticles, similar to the assembly of gold nanospheres. We observe, however, that side-by-side linkage of nanorods in solution shows a blue-shift of the longitudinal plasmon band and a red-shift of the transverse plasmon band. Optical spectra calculated using the discrete dipole approximation method were used to simulate plasmon coupling in assembled nanorod dimers. The longitudinal plasmon band is found to shift to lower energies for end-to-end assembly, but a shift to higher energies is found for the side-by-side orientation, in agreement with the optical absorption experiments. The strength of plasmon coupling was seen to increase with decreasing internanorod distance and an increase in the number of interacting nanorods. For both side-by-side and end-to-end assemblies, the strength of the longitudinal plasmon coupling increases with increasing nanorod aspect ratio as a result of the increasing dipole moment of the longitudinal plasmon. For both the side-by-side and end-to-end orientation, the simulation of a dimer of nanorods having dissimilar aspect ratios showed a longitudinal plasmon resonance with both a blue-shifted and a red-shifted component, as a result of symmetry breaking. A similar result is observed for a pair of similar aspect ratio nanorods assembled in a nonparallel orientation. The internanorod plasmon coupling scheme concluded from the experimental results and simulations is found to be qualitatively consistent with the molecular exciton coupling theory, which has been used to describe the optical spectra of H and J aggregates of organic molecules. The coupled nanorod plasmons are also suggested to be electromagnetic analogues of molecular orbitals. Investigation of the plasmon coupling in assembled nanorods is important for the characterization of optical excitations and plasmon propagation in these nanostructures. The surface plasmon resonance shift resulting from nanorod assembly also offers a promising alternative for analyte-sensing assays.     

Use of capillary electrophoresis for characterisation of vinyl‐terminated Au nanoprisms and nanooctahedra

It is described a simple, rapid and efficient methodology to characterise and separate gold nanoprisms and nanooctahedra by capillary electrophoresis. This technique is suitable to distinguish between morphologies and it can be used as a powerful separation tool after a customised synthesis of both structures. This synthesis was carried out by amending two parameters, temperature and pH, and a sharp decrease was found in nanotriangles when temperature was increased from 70 up to 95°C. However, when the synthesis was performed at a given temperature, an increase in pH did not promote an important change in isolation of any structure until pH = 9.5, critical in the final morphology of the nanoparticle. Gold nanoprisms and nanooctahedra were successfully separated by capillary electrophoresis according to differences in charge‐to‐mass ratio of the morphologies. Final particle morphology was confirmed by transmission electron microscopy analysis. Under optimal working conditions, a mixture containing both shapes of gold nanoparticles was initially injected and two major peaks were obtained for each structure. Capillary electrophoresis allowed to study pH and temperature influence on both morphologies. It was inferred that the ratio between triangles and octahedra decreased to a great extent when increasing both temperature and pH.     

Optical properties of Au-Ag nanoboxes studied by single nanoparticle spectroscopy

The optical properties of two Au-Ag nanobox samples with average edge lengths of 44 and 58 nm and wall thicknesses of 6 and 8 nm, respectively, have been studied by single particle spectroscopy. The measurements gave an average line width of Gamma = 306 +/- 7 meV with a standard deviation of sigma = 30 meV for the 44-nm boxes, and Gamma = 350 +/- 9 meV with sigma = 35 meV for the 58-nm boxes. These line widths are much broader than those of gold nanorods with comparable resonance energies. The increased broadening is attributed to a combination of surface scattering of electrons, as well as increased radiation damping for the nanoboxes. Discrete dipole approximation calculations have been performed with and without surface scattering of electrons to compare with the experimental spectra. The calculations confirm that both electron-surface scattering and radiation damping are important effects in this system.     

Single-crystalline gold microplates: synthesis, characterization, and thermal stability

Single-crystalline gold microplates of several 10 microm in lateral size, characterized by hexagonal, truncated triangular, and triangular shapes with (111) planes as two basal surfaces, have been synthesized in large quantities through a solution phase process. Significantly, such anisotropic Au nanostructures exhibit remarkable optical properties, in which the dipole plasmon resonance shifting in the NIR region and the quadrupole plasmon resonance at approximately 820 nm were observed. Fragmentation of Au microplates is found when the temperature is higher than 450 degrees C, indicating they are not thermodynamically stable structure at high temperature. Investigations on the Au microplates upon heating suggest that the melting and collapsing start mainly at the edges that should be Au (110) facets. This work is valuable for Au nanostructures applied at elevated temperatures.     

Predication of second-order optical nonlinearity of [(Bu2t Im)AuX] (X=halogen) using time-dependent density-functional theory combined with sum-over-states method

The dipole polarizability and second-order polarizability of recently synthesized (1,3-di-ter-butylimidazol-2-ylidine) gold complexes [(Bu2t Im)AuX] (X=halogen) were investigated by using time-dependent density-functional theory combined with sum-over-states method. We have discovered that these complexes possess remarkably larger molecular second-order polarizability compared with the organometallic and organic complexes. The value of the second-order polarizability increases in the order of F相似文献   

Green, effective chemical route for the synthesis of silver nanoplates in tannic acid aqueous solution

Silver nanoplates, with average size tunable from 50 to 500 nm, have been synthesized via a simple room-temperature tannic acid (TA) solution-phase chemical reduction method. The synthesis was a seedless process in which tannic acid was used as a reducing as well as a capping agent, and did not need any other surfactant or capping agent to direct the anisotropic growth of the silver nanoparticles. The morphology of silver nanoplates has been confirmed by transmission electron microscopy, the growth process of nanoplates has been studied by UV/vis spectroscopy. Control experiments have been explored for a more thorough understanding of the growth mechanism. It was found that both the concentrations of TA and the pH of solution were the key elements to control the morphology silver nanoplates. The optical in-plane dipole plasmon resonance bands of these silver plates could be tuned from 520 to 1100 nm.     

Tailoring the synthesis and heating ability of gold nanoprisms for bioapplications

The paper describes a novel and straightforward wet-chemical synthetic route to produce biocompatible single-crystalline gold tabular nanoparticles, herein called nanoprisms (NPRs) due to their characteristic shape. Besides the novelty of the method to produce NPRs with an unprecedented high yield, the synthesis avoids the use of highly toxic cetyltrimethylammonium bromide (CTAB), the most widely used surfactant for the synthesis of gold anisotropic nanoparticles such as nanorods or nanoprisms. The method presented here allows for tuning the edge length of NPRs in the range of 100-170 nm by adjusting the final concentration/molar ratio of gold salt and reducing agent (thiosulfate), while the thickness of NPRs remained constant (9 nm). Thus, the surface plasmon band of NPRs can be set along the near-infrared (NIR) range. The resulting NPRs were derivatized with heterobifunctional polyethylene glycol (PEG) and 4-aminophenyl β-D-glucopyranoside (glucose) chains to improve their stability and cellular uptake, respectively. The heating properties of colloidal solutions of NPRs upon 1064 nm light illumination were evaluated. As a proof of concept, the biocompatibility and suitability of functional NPRs as photothermal agents were studied in cell cultures. Due to their biocompatibility (avoiding CTAB), ease of production, ease of functionalization, and remarkable heating features, the NPRs discussed herein represent a significant advance in the biocompatibility of nanoparticles and serve as an attractive alternative to those currently in use as plasmonic photothermal agents.     

Improving surface plasmon resonance imaging of DNA by creating new gold and silver based surface nanostructures

The use of nanoparticles (NPs) can substantially improve the analytical performance of surface plasmon resonance imaging (SPRi) in general, and in DNA sensing in particular. In this work, we report on the modification of the gold surface of commercial biochips with gold nanospheres, silica-coated gold nanoshells, and silver nanoprisms, respectively. The NPs were tethered onto the surface of the chip and functionalized with a DNA probe. The effects of tethering conditions and varying nanostructures on the SPRi signals were evaluated via hybridization assays. The results showed that coupling between planar surface plasmons and electric fields, generated by localized surface plasmons of the NPs, is mandatory for signal enhancement. Silver nanoprisms gave the best results in improving the signal change at a target DNA concentration of <50 nM by +50 % (compared to a conventional SPRi chip). The limit of detection for the target DNA was 0.5 nM which is 5 times less than in conventional SPRi.

The optically detected coherent lattice oscillations in silver and gold monolayer periodic nanoprism arrays: the effect of interparticle coupling

Using femtosecond transient spectroscopy, we studied the optically detected laser-induced coherent phonon oscillation of monolayers of periodic arrays of prismatic-shaped silver and gold nanoparticles, assembled by using the technique of nanosphere lithography. In this method, the same size of polystyrene sphere and the same vacuum conditions are used. Under these circumstances, the gold nanoprisms formed are found to have sharper tips than the corresponding silver nanoprisms. For both gold and silver nanoparticles, the surface plasmon absorption maximum is found to depend linearly on size. The coherent lattice oscillation periods are also found to depend linearly on size. However, although the observed dependence for the silver nanoparticle is found to follow the calculated dependence of a single particle on size (based on a one-dimensional standing wave model), the gold nanoparticle deviates from this model, and the deviation is found to increase with the size of the nanoparticles. This deviation can be explained by considering interparticle coupling. A simple interparticle lattice oscillating dipolar coupling model of the dimer is found to qualitatively account for both the sign and the size dependence of the deviation. The absence of this deviation in the silver nanoparticle arrays is blamed on the weak interparticle coupling due to their rounded tips and the possibility of oxidation of their surfaces.     

Dipole-dipole plasmon interactions in gold-on-polystyrene composites

Red-shifting of the optical absorption spectra of aggregates of gold nanoparticles by dipole-dipole interactions is of considerable interest, both for theoretical reasons and because the phenomenon can be potentially exploited in various applications. A convenient and practical way to control the effect is to assemble the aggregated ensemble of n gold nanoparticles on the outer surface of larger dielectric spheres. Here, we show by experiment and calculation how the spectra of these structures can be systematically morphed from that of isolated gold particles, through the regime of broad absorption dominated by particle-particle interactions, and finally to the limiting case of a continuous nanoshell. The experimental data were produced using the process of deposition-precipitation, which provides a facile method to decorate polystyrene microspheres with gold nanoparticles. There is no need for prior functionalization of the microsphere surface in our method of deposition-precipitation. Calculations were carried out using a code based on the discrete dipole approximation (DDA). The spectra were dominated by three effects. These were a peak absorption at about 540 nm produced by the conventional plasmon resonance of spherical gold nanoparticles, a broad absorption in the range 600-900 nm caused by diverse dipole-dipole interactions between particles, which strengthened as the number of attached gold particles increased and finally, when n was large, an absorption peak due to the onset of nanoshell-like resonances. The experimental spectra could be successfully fitted by spectra calculated using combinations of these effects.