High Aspect Ratio Gold Nanorods Research Articles

Synthesis of Asymmetric One-Dimensional Pd on Au Bimetallic Nanostructures.

Nanostructures composed of a gold nanorod (AuNR) core and a Pd/Pt shell are of great interest due to their potential application as plasmon resonance-enhanced catalysts. However, the synthesis of well-defined one-dimensional bimetallic nanostructures with precise control over shell thickness and length remains a challenge. In this study, we report a detailed and systematic study on the chemical synthesis of a uniform Pd shell on single crystalline and pentahedrally twinned (PHT) AuNRs of various lengths. AuNRs were used as a template, and the slow and controlled reduction of Pd(II) ions on preformed AuNRs was carried out for the formation of rectangular-shaped Au@Pd bimetallic nanorods. The Pd shell thickness around the AuNRs was controlled by the supply of Pd(II) ions in the growth solution. We were able to grow a ∼20 nm uniform Pd shell around the AuNR, keeping the rod-like morphology intact without local nucleation to form irregular shapes and randomly overgrown nanostructures. The formation of bimetallic nanorods was also extended beyond typical single crystalline nanorods to PHT high aspect ratio gold nanorods and nanowires, using them as templates. To our surprise, unusually curved asymmetric nanorods were formed when the Pd deposition was carried out on AuNRs longer than ∼800 nm which could be possibly due to a Pd and Au lattice mismatch at the interface and higher flexibility of the nanorods when they exceeded certain lengths.

Fractionation and Characterization of High Aspect Ratio Gold Nanorods Using Asymmetric-Flow Field Flow Fractionation and Single Particle Inductively Coupled Plasma Mass Spectrometry

Gold nanorods (GNRs) are of particular interest for biomedical applications due to their unique size-dependent longitudinal surface plasmon resonance band in the visible to near-infrared. Purified GNRs are essential for the advancement of technologies based on these materials. Used in concert, asymmetric-flow field flow fractionation (A4F) and single particle inductively coupled mass spectrometry (spICP-MS) provide unique advantages for fractionating and analyzing the typically complex mixtures produced by common synthetic procedures. A4F fractions collected at specific elution times were analyzed off-line by spICP-MS. The individual particle masses were obtained by conversion of the ICP-MS pulse intensity for each detected particle event, using a defined calibration procedure. Size distributions were then derived by transforming particle mass to length assuming a fixed diameter. The resulting particle lengths correlated closely with ex situ transmission electron microscopy. In contrast to our previously reported observations on the fractionation of low-aspect ratio (AR) GNRs (AR < 4), under optimal A4F separation conditions the results for high-AR GNRs of fixed diameter (≈20 nm) suggest normal, rather than steric, mode elution (i.e., shorter rods with lower AR generally elute first). The relatively narrow populations in late eluting fractions suggest the method can be used to collect and analyze specific length fractions; it is feasible that A4F could be appropriately modified for industrial scale purification of GNRs.

High Aspect Ratio Gold Nanorods Grown with Platinum Seeds

Using Au chloride as precursor, Pt nanocrystals as seeds, ascorbic acid as a reducer, and CTAB as surfactant and complexing agent, extremely long Au nanorods have been grown. The influence of different parameters such as the composition of the seeds, the amount of Pt, or the type of Pt present in solution has been analyzed. These large Au NRs have been exhaustively characterized by (S)TEM, SEM and optical microscopy as well as UV–vis spectroscopy and their morphology correlated with the growth mechanism.

Colorimetric detection of glutathione based on transverse overgrowth of high aspect ratio gold nanorods investigated by MCR-ALS

In this paper, we present a simple platform for colorimetric detection of glutathione using gold nanorods (AR ∼ 6.5 ± 0.2) as a plasmonic sensor.

Seedless synthesis of high aspect ratio gold nanorods with high yield

A seedless method has been developed for the synthesis of high aspect ratio gold nanorods. Gold nanorods with a longitudinal surface plasmon resonance of larger than 1400 nm were synthesized in one step. The yield was high, and no purification step was needed. We also synthesized normal aspect ratio gold nanorods by a seedless method. The conditions for the synthesis of uniform gold nanorods with different width and aspect ratio by a seedless method were explored. A better understanding of the seedless method enables the facile synthesis of nanomaterials with a broader size tunability and better reproducibility.

High aspect ratio gold nanorods displayed augmented cellular internalization and surface chemistry mediated cytotoxicity

Due to their unique properties, gold nanorods (GNRs) have shown tremendous potential for advancing bio-imaging and sensing applications. As these nanoparticles display size-dependent optical properties, high aspect ratio GNRs are of particular interest for these applications because of their increased scattering contrast. While studies are emerging that demonstrate successful synthesis of high aspect ratio GNRs, their behavior and fate in a physiological environment has yet to be investigated. The goal of this study was to evaluate the rate of cellular internalization and cytotoxicity of long GNRs (aspect ratio 32) in a human keratinocyte cell line. Additionally, the critical role of surface chemistry in extent of cellular interactions and cytotoxicity was evaluated. Through comparison with aspect ratio 3 GNRs, it was identified that high aspect ratio GNRs displayed enhanced cellular internalization. Furthermore, surface functionalization dictated the quantity of GNRs internalized, with tannic acid having a significant increase over polyethylene glycol. However, the augmented intracellular concentration identified with long, tannic acid GNRs resulted in a considerable degree of cytotoxicity, which was not associated with other GNR conditions. Therefore, while the inclusion of high aspect ratio GNRs may increase the capabilities for nano-based applications, there exist some unintentional toxicological consequences that must also be considered.

Orientation Sensing with Color Using Plasmonic Gold Nanorods and Assemblies.

Colorimetric analysis of broadband illumination scattered from isolated gold nanorods and reduced symmetry Dolmen structures provide a visible measure of the local nanoscale orientation of the nanostructures relative to the laboratory frame of reference. Polarized dark-field scattering microscopy correlated with scanning electron microscopy of low and high aspect ratio gold nanorods demonstrated accuracies of 2.3 degrees, which is a 5-fold improvement over photothermal and defocused imaging methods. By assigning the three color channels of the imaging detector (red, green, and blue) to the plasmon resonance wavelengths of the nanostructure, the quantitative display of orientation improved by 200%. The reduced symmetry of a gold nanorod Dolmen structure further improved the sensitivity of colorimetric orientation by a factor of 2 due to the comparative intensities of the resonances. Thus the simplicity, high accuracy, and sensitivity of visual colorimetric sensing of local nanoscale orientation holds promise for high throughput, inexpensive structure and dynamics studies in biology and material science.

Spiked Gold Beads as Substrates for Single‐Particle SERS

We introduce a new family of spiked particles resulting from the growth of high aspect ratio gold nanorods. Upon spike growth, elongated beads are obtained with sizes above 300 nm. Interestingly, and in contrast to smooth particles of the same size, these spiked-particles are not only able to sustain localized surface plasmon resonances and consequently enhance Raman signals, but are also big enough to be recognized by standard confocal optical microscopy. These spiked beads have been engineered into thin films to test their surface-enhanced Raman scattering (SERS) enhancing efficiency as a function of the particle density. Such films provide a high level of portability and easiness of use for "in-field" optical ultrasensitive analysis.

Synthesis of high aspect ratio gold nanorods and their effects on human antigen presenting dendritic cells

High aspect ratio (AR) gold nanorods (NRs) attract great interest for biomedical applications due to their novel physicochemical properties. Here, we report a facile method for preparation of high ...

Towards a Reproducible Synthesis of High Aspect Ratio Gold Nanorods

The seed-mediated method in presence of high concentrations of CTAB is frequently implemented in the preparation of high aspect ratio gold nanorods (i.e., nanorods with aspect ratios of 5 or more); however, the reproducibility has still been limited. We rendered the synthesis procedure simpler, decreased the susceptibility to impurities, and improved the reproducibility of the product distribution. As a result of the high aspect ratios, longitudinal plasmon absorptions were shifted up to very high absorption maxima of 1955 nm in UV-vis-NIR spectra (since this band is completely covered in aqueous solution by the strong absorption of water, the gold species were embedded in poly(vinyl alcohol) films for UV-vis-NIR measurements). Finally, the directed particle growth in (110) direction leads to the conclusion that the adsorption of CTAB molecules at specific crystal faces accounts for nanorod growth and not cylindrical CTAB micelles, in agreement with other observations.

PH Controlled Synthesis of High Aspect-Ratio Gold Nanorods

Here we report the two-step synthesis of high aspect-ratio gold nanorods via combining low pH growth and higher cetyltrimethylammonium bromide concentration. The approach is motivated by the "slow growth principle," which has been demonstrated recently as a effective protocol to prepare high aspect-ratio one-dimensional nanostructures. When the pH value of the growth solution gradually decreased, the growth rate of nanorods was significantly decreased and a continuous morphological changing from uniform monodisperse gold nanospheres to extraordinary long gold nanorods occured. By simultaneously decreasing the growth pH and increasing the concentration of cetyltrimethylammonium bromide, the length of gold nanorods could be further elongated to above 2 μm with large aspect-ratio of above 80. This kind of high aspect-ratio gold nanorods could be excellent building blocks for optical or electrical nanodevices in future.

Purification of High Aspect Ratio Gold Nanorods: Complete Removal of Platelets

Because physical and chemical properties of nanostructures strongly depend on their shape, it is of great importance to find either synthetic or separation techniques that can produce objects of a particular shape in a pure state. This manuscript describes a solution to a long standing problem of separating 2D platelets from 1D nanorods. The key aspect of our approach relies on the partial dissolution of faceted platelets with Au(III)/CTAB complex that transforms them into smaller nanodisks. Because of the reduction in size, the 2D structures become fully soluble in water and can be separated from the nanorods that undergo slow precipitation. In addition, the isolated nanodisks can be converted back into initial faceted platelets upon treatment with Au(I)/ascorbic acid mixture. As a result of these simple procedures, a seemingly inseparable mixture of rods, platelets, and spheres is converted into nearly pure individual components.

Luminescent Silicon Nanoparticles Formed in Solution

Here we report the two-step synthesis of high aspect-ratio gold nanorods via combining low pH growth and higher cetyltrimethylammonium bromide concentration. The approach is motivated by the "slow growth principle", which has been demonstrated recently as a effective protocol to prepare high aspect-ratio one-dimensional nanostructures. When the pH value of the growth solution gradually decreased, the growth rate of nanorods was significantly decreased and a continuous morphological changing from uniform monodisperse gold nanospheres to extraordinary long gold nanorods occured. By simultaneously decreasing the growth pH and increasing the concentration of cetyltrimethylammonium bromide, the length of gold nanorods could be further elongated to above 2 microm with large aspect-ratio of above 80. This kind of high aspect-ratio gold nanorods could be excellent building blocks for optical or electrical nanodevices in future.

Direct High-Yield Synthesis of High Aspect Ratio Gold Nanorods

We report a new development for the direct high-yield synthesis of high aspect ratio gold nanorods. By using a modified seed-mediated synthesis approach for the preparation of high aspect ratio gol...

Two-step synthesis of high aspect ratio gold nanorods

AbstractWe describe a very simple, two-step synthetic method to prepare gold nanorods with extremely high aspect ratios (> 20) and average lengths of more than 1000 nm. The method is based on a seed-mediated growth in presence of the surfactant cetyltrimethylammonium bromide. The length and aspect ratios of the nanorods can be manipulated by varying the surfactant concentration.

Seed-Mediated Synthesis of High Aspect Ratio Gold Nanorods with Nitric Acid

We report a new approach for the seed-mediated synthesis of gold nanorods with high aspect ratios by the addition of nitric acid. Various amounts of nitric acid were added during nanorod growth to significantly enhance the production of high aspect ratio nanorods. The resulting nanorods have uniform diameters of 19−20 nm and can reach lengths of 400−500 nm to yield nanorods with average aspect ratios of 21−23. The nanorods represent a large fraction of the gold nanostructures synthesized, with triangular, truncated triangular, and hexagonal nanoplates about 120−200 nm in width making up rest of the gold nanostructures formed. These nanorods spontaneously self-assemble into a high-density three-dimensional packing structure with the nanorods arranged side-by-side and end-to-end. These nanorods possess a 5-fold twinned structure with ten {111} end faces and five {100} side faces. UV−vis absorption spectrum shows a transverse plasmon absorption band at 508 nm. The longitudinal plasmon absorption band should appear beyond 2500 nm due to the extremely long length of these nanorods. The presence of nitrate ions, rather than the slight pH change caused by nitric acid, is believed to have a greater effect on the formation of these nanorods.

Gold Nanorods Grown Directly on Surfaces from Microscale Patterns of Gold Seeds

We report a strategy for patterning surfaces with high aspect ratio gold nanorods (Au NRs) by using a poly(dimethylsiloxane) (PDMS) stamp to microcontact print 3−5 nm diameter gold nanoparticle (Au NP) “seeds” onto mercaptan-functionalized Si/SiOx surfaces and subsequently grow the seeds into Au NRs via seed-mediated reduction of HAuCl4 with ascorbic acid in the presence of cetyltrimethylammonium bromide (CTAB). The patterns also contain a large number of spherical particles, which are largely removed and separated from NRs using adhesive tape. The same PDMS stamp was used more than 30 times to produce well-defined patterns without reinking with Au NP seeds. Controlled patterning of Au NRs on surfaces is important for electronics, sensing, optical, and plasmonic applications.

Seed Mediated Growth of Gold Nanoparticles on Indium Tin Oxide Electrodes: Electrochemical Characterization and Evaluation

AbstractThe seed mediated growth of gold nanoparticles on indium tin oxide (ITO) surfaces is described, which provided a new method for the construction of gold nanoparticles‐modified ITO electrodes even without using conventional linker molecules, such as (3‐mercaptopropyl)trimethoxysilane (MPTMS). In this process, ultra‐small gold seeds were formed and anchored on the ITO surfaces first. When the seeds‐deposited ITO surfaces came into contact with the gold growth solution, the growth of gold nanoparticles occurred. The morphology of the as‐prepared modified surface was found to be strongly dependent upon the substrate. On an MPTMS‐silanized ITO, mostly gold nanospheres were formed (Au/MPTMS/ITO).In contrast, on a bare ITO, some high aspect ratio gold nanorods as well as large amounts of gold nanospheres were grown and directly attached (Au/ITO). The as‐prepared two gold nanoparticles‐modified ITO electrodes exhibited different electrochemical characteristics, attributed to the influence of MPTMS molecules. Compared with Au/MPTMS/ITO, the Au/ITO was more efficient in decreasing the heterogeneous charge transfer resistance and improving the reaction reversibility of [Fe(CN)6]3−/[Fe(CN)6]4− and exhibited more attractive bioelectrocatalytic properties. Due to the block effect of the thiol monolayer, Au/MPTMS/ITO depressed the selectivity for the determination of epinephrine (EP) in the presence of ascorbic acid (AA) while Au/ITO could improve the detection sensitivity and retain the selectivity.

Synthesis and Manipulation of High Aspect Ratio Gold Nanorods Grown Directly on Surfaces

Here we describe the synthesis of Au nanorods directly on glass surfaces using seed-mediated deposition of Au from AuCl4- onto surface-attached 3-5 nm diameter Au nanoparticles (AuNPs) in the presence of cetyltrimethylammonium bromide (CTAB). The average length (200 nm to 1.2 microm) and aspect ratio (6-22) of the nanorods increases with increasing AuCl4- concentration. Short, low aspect ratio Au nanorods are manipulated with an atomic force microscopy (AFM) tip, while longer, high aspect ratio nanorods are bent and broken with the AFM tip.

Liquid crystalline assemblies of ordered gold nanorods

Gold nanorods have been prepared in aqueous solution using a seed-mediated growth approach in the presence of surfactant. We observe the formation of liquid crystalline phases in concentrated solutions of high aspect ratio (13–18) gold nanorods by polarizing microscopy, transmission electron microscopy, and small angle X-ray scattering. These phases, which are stable up to 200 °C, exhibit concentration-dependent orientational order.