Tunable Hollow Metal Nanorods- A Novel Approach

An adaptable approach for preparing nano-materials of engineered size, shape, composition, and porosity has been developed by researchers at Simon Fraser University, Canada.
They have developed a simple technique to engineer hollow metal nanostructures of well-defined properties.
The nanostructures have a tunable diameter, length, and shape that are defined by the sacrificial template used to grow the hollow product. The electrochemically synthesized templates are
regular, polycrystalline cylindrical silver nanorods with dimensions dictated by both the physical mold that confines their growth as well as the conditions for electrodeposition. This template can be selectively etched to isolate a porous hollow nanostructure.
These robust hollow metal nanostructures have potential applications in the selective delivery and release of reagents such as medicinal drugs.
The photothermal properties of metal nanostructures have been investigated for destroying cancer cells.


Reference: ACSNano,VOL.3,NO. 6, 1365–1372 , 2009

Thiolate Ligand Stabilization of Gold Nanoparticles

Polydentate amphiphilic thiols possess excellent properties for gold nanoparticle stabilization and functionalization and resistant to exchange reactions.

Gold -thiol bond is generally believed to be one of tightest link for gold surface functionalization and well-known for its thermodynamic stability. In biological environment, where thiol groups are presents, prevention of thiolate-thiol excahnge is also an important consideration. In such situations, a reliable functionalization can provide kinetic stability against ligand exchange.

Different efforts have been made to improve the exchange stability of thiolate ligands on gold nanoparticles.
Recently, German scientist have synthesized the trithiol
1,1,1-tris(mercaptomethyl)undecane as a model to investigate the particle stabilization and exchange properties of tripodal organothiolate.

for further details, refer to: Chem. Commun., 2006, 3693–3695 | 3693

Cancer Photothermal Therapy using Gold Nanoshells

Almost all available hyperthermic techniques for cancer tumor therapy suffers with low spatial selectivity in the heating of tumors and surrounding healthy tissues.A new approach to overcome this limitation has been developed over last five years and it has been called 'plasmonic photothermal therapy(PPTT).

In this approach tumor tissues are labeled by gold(or silver) nanoparticle with different shapes and structures. By exposing nanoparticles to laser radiation near their plasmon-resonant absorption, it is possible to produce local heating of labeled cells without harming the healthy ones.

Recently, Scientists from Russia have used plasmonic silica/gold nanoshells to produce a controllable laser hyperthermia.They have synthesized gold nanoshells with very high extinction in the NIR spectral range.Laser irradiation parameters are optimized on the basis of experiments conducted using test-tube phatom and laboratory rats.Thermal imaging system is used for studying temperature distribution on the animal skin surface athypodermic and intramuscular injection of gold nano-shells.

For more details refer to : Journal of Biomedical Optics 14(2), 021016

Recent Study of Growth Kinetic for Gold Nanorods

For the first time, scientists at Mainz University, Germany have  reported the growth kinetic model for the formation of gold nanorods by combining Small-angle X-ray scattering(SAXS) and optical extinction spectroscopy.

Despite several in situ (dark-field microscopy) and ex situ (electron microscopy) studies of metal nanoparticle growth, the anisotropic growth kinetics was not well-understood until now mainly because the crystallization is a nonequilibrium process. Using simultaneous optical spectroscopy and time-resolved small-angle X-ray scattering at a synchrotron X-ray source, Researchers directly monitor the anisotropic growth kinetics of gold  nanorods and extract the growth parameters for both crystal directions (along the rod’s long and short axes) independently. They have found that a crossover from 1D to 3D growth modes at 8 and 12 min, respectively, where the nanorods attain their maximum aspect ratio. The growth model explains and predicts this crossover point without the need of a switch for the growth mode and allows for the fine-tuning of the particle shapes.

From their study, The Researchers concluded that the time evolution of nanorod formation extracted in parallel with SAXS and optical spectroscopy shows a simple exponentially decreasing growth rate. The initial growth rate in the long nanorod direction is 5 times larger than that in the short axis direction. Both rates decrease exponentially with a slightly faster time constant for the long axis, which leads to a switch from 1D to 3D growth after about 8−12 min and reduces the aspect ratio of the final products to about 3. 

Researcher believe that the experimentally determined time constants and growth models discussed in their work will aid the development of more detailed molecular simulations for gold nanorod growth.

High storage-DVDs created using gold-nanorods

Researchers at the Swinburne University of Technology, in Hawthorn, Australia, have found a way to add two more dimensions to optical-disc recording: wavelength and polarization. The technique could pack 1.6 terabytes of data on a standard-size DVD, —the equivalent of 30 Blu-ray discs. Moreover, it could be compatible with today’s disk-drive technology.
The Australian researchers are very optimistic about this new technology. They say that data recording could be done with a cheaper laser diode and that high-speed recording and readout should be possible. They have signed a research agreement with Samsung and believe that the technology will be available commercially in 5 to 10 years.

Their research involves making a new kind of disc. They dispersed gold nanorods of three different sizes in a polymer solution, coated thin glass films with the solution, and then used glue to assemble a stack of three of the films, one on top of the other.

For recording the disc, a tunable laser is focussed on 750-nanometer-wide spots on a gold nanorod layer. The tiny rods have a tendency to collapse into spheres when they absorb light and are heated to a certain threshold. But the rods are selective. Nanorods of a specific size absorb a specific wavelength and then only if they are aligned with the direction of the light’s polarization. Under those conditions, the energy waves traveling along the rods’ surface—called surface plasmons—resonate with the light’s frequency. So when the laser beam is focused on the bits, only some of the rods turn into spheres.

There are many different sizes of rods in random orientation.Light impinging with a certain color and polarization will only target a subpopulation of gold nanorods, leaving the remaining rods for the next recording. That means each bit area can hold multiple bits. To demonstrate the technology, reserachers created six patterns on each of the three nanorod layers by focusing light on a grid of 75-by-75 bits. The volume of their disk is about 12 cm³, which gives a total data capacity of 1.6 terabytes.

Reading the bits involves focusing light from the same laser on the bits but with much lower energy. The nanorods shine when they absorb the dim light, which must be of the same wavelength and polarization that could change their shape during recording.

People have been thinking about 3-D optical data storage for a while, but this is the first time data has been recorded and read in five dimensions

Identification of Additional Plasmon Mode for Triangular Gold Nanoprism

The use of anisotropic nanomaterials in applications such as biodetection,catalysis,and electronics has led to a continuously increasing interest in the development of synthetic methods for preparing new shapes.
In particular,triangular nanoprisms are a class of nanostructures that have generated intense interest due to their unusual optical properties and the recent development of new methodologies for preparing bulk quantities of them. Gold nanoprisms have been synthesized exclusively by thermal methods with varying degrees of success regarding purity and size control.The optical spectra of nanoprisms should exhibit a distinct dipole resonance as observed in isotropic spherical structures in addition to weaker higher order resonances.The identification of higher order surface plasmon resonance modes with these nanostructures is important because it provides not only greater understanding of their physical properties but also a spectroscopic fingerprint that can be used to characterize and assess the quality of such structures. Recently researchers presented a synthetic approach and separation procedure for synthesizing and isolating large quantities of gold nanoprisms with uniform edge lengths and thicknesses, which has allowed the use of UV−vis−NIR spectroscopy to observe an in-plane quadrupole resonance mode of such structures.
The researchers have develop a method for synthesizing Au nanoprisms in their purest form. The purity of such materials has allowed them to correlate their structure with their optical properties and identify the quadrupole plasmon resonance, which has never been observed in solution because of inhomogeneity and impurities found in the products formed from other preparatory procedures. In view of the high stability of gold as compared with silver, these structures should provide a route to synthesizing many technologically useful materials not attainable with their less noble analogue.

Gold Nanorods Assemblies with Nano Gaps

Gold nanorods continue to gather increasing interest due to their facile synthesis, unique optical properties, and potential for medical and electronic applications. To take advantage of these properties, several research groups are pursuing methods to self-assemble or to arrange these nanomaterials into useful formations.End-to-end assemblies are of particular appeal since gaps between the nanorods could serve as spacers for single-molecule electronic devices. Several successful approaches to accomplish end-to-end assembly have been reported in the literature; however, each of these approaches relies on modifying already synthesized gold nanorods by adding the desired linker agent.

Seeking a new bottom-up technique to generate gold nanorods assembled end-to-end, researchers have developed a novel method to grow the rods directly from chemically linked seed particles. The researchers started with citrate-stabilized gold nanoparticles, then allowed these seeds to self-assemble using a water-soluble dithiol-functionalized polyethylene glycol linker. The seed particle dimers were then exposed to growth conditions similar to those typically used to form unlinked gold nanorods, extending each rod to a length of 500 nm. About 55% of the rods grown using this method were linked end-to-end. Transmission electron microscopy revealed a gap of 1−2 nm between these linked rods, a size well-suited for placing a single molecule within the gap. The linked nanorods were flexible around the hinging molecule, demonstrated by flow linear dichroism. The researchers suggest that exposing the linked nanorods to a low-concentration solution of an electronically relevant molecule would result in one or a few molecules within each nanogap, enabling single-molecule electronic measurements.