Spherical Gold Nanostructures Research Articles

Nanostars Carrying Multifunctional Neurotrophic Dendrimers Protect Neurons in Preclinical In Vitro Models of Neurodegenerative Disorders.

A challenge in neurology is the lack of efficient brain-penetrable neuroprotectants targeting multiple disease mechanisms. Plasmonic gold nanostars are promising candidates to deliver standard-of-care drugs inside the brain but have not been trialed as carriers for neuroprotectants. Here, we conjugated custom-made peptide dendrimers (termed H3/H6), encompassing motifs of the neurotrophic S100A4-protein, onto star-shaped and spherical gold nanostructures (H3/H6-AuNS/AuNP) and evaluated their potential as neuroprotectants and interaction with neurons. The H3/H6 nanostructures crossed a model blood–brain barrier, bound to plasma membranes, and induced neuritogenesis with the AuNS, showing higher potency/efficacy than the AuNP. The H3-AuNS/NP protected neurons against oxidative stress, the H3-AuNS being more potent, and against Parkinson’s or Alzheimer’s disease (PD/AD)-related cytotoxicity. Unconjugated S100A4 motifs also decreased amyloid beta-induced neurodegeneration, introducing S100A4 as a player in AD. Using custom-made dendrimers coupled to star-shaped nanoparticles is a promising route to activate multiple neuroprotective pathways and increase drug potency to treat neurodegenerative disorders.

Plasmon-enhanced photoluminescence from TiO2 and TeO2 thin films doped by Eu3+ for optoelectronic applications.

In this work we study the luminescence properties of europium-doped titanium dioxide and tellurium oxide thin films enhanced by gold plasmonic nanostructures. We propose a new type of plasmon structure with an ultrathin dielectric film between plasmonic platform and luminescent material. Plasmonic platforms were manufactured through thermal annealing of the gold thin film. Thermal dewetting of gold film results in spherical gold nanostructures with average dimensions of 50 nm. Both, luminescent TiO2:Eu and TeO2:Eu films were deposited by RF magnetron sputtering from mosaic targets. The morphology of the gold nanostructures was investigated by SEM and TEM, while the composition of oxides film was analyzed by XPS. Luminescence properties were studied on the basis of excitation and emission spectra. The experiments show that the additional dielectric layer enhances the luminescence intensity. Such structures could be potential candidates as phosphors in white LEDs.

Bifunctional Diblock DNA-Mediated Synthesis of Nanoflower-Shaped Photothermal Nanozymes for a Highly Sensitive Colorimetric Assay of Cancer Cells.

The activity of a nanozyme is closely related to its surface area-to-volume ratio and the surrounding temperature. To acquire highly active nanozymes, one-pot metallization-like synthesis of novel nanoflower-shaped photothermal nanostructures was conducted using polyadenine-containing diblock DNA as the scaffold. The nanoflower-shaped structures with a high surface area-to-volume ratio and photothermal performance exhibited excellent peroxidase-mimicking activity, and the biorecognition capability was retained by the capping agent of diblock DNA. The functionalized nanostructures were used for a proof-of-concept colorimetric assay of cancer cells in vitro. Upon incorporation of 808 nm laser irradiation, high sensitivity and selectivity for the cancer cell assay were achieved with the lowest detection level of 10 cells/mL. Relative to spherical gold nanostructures, the nanoflower-shaped photothermal nanozyme exhibited higher assay sensitivity, paving the way for the construction of nanozyme-based colorimetric sensors for point-of-care testing.

Computational characterization of plasma effects in ultrafast laser irradiation of spherical gold nanostructures for photothermal therapy

Ultrashort pulsed lasers can provide high peak intensity with low pulse fluence. This makes them an ideal choice in photothermal therapy and applications where damage to the surrounding material needs to be minimized. Depending on the peak intensity, the ultrashort pulsed laser’s interaction with matter can lead to plasma formation through nonlinear effects such as multiphoton and impact electron excitation. The capability of the spherical gold nanoparticles, as the most employed nanoparticle so far for photothermal therapy, to enhance and strongly localize the incident laser field leads to plasma formation around the particles at even lower pulse fluences. Under certain circumstances, during the pulse duration, this plasma can absorb more energy than the nanoparticle itself. Consequently, the absorbed energy by the generated plasma can act as an energy source for different phenomena such as the evolution of the temperature distribution, thermoelastic stress generation, and stress-induced bubble formation. In this paper, we study the plasma-mediated interaction of a 45 fs pulsed laser with two types of spherical gold nanoparticles in water: solid nanoparticle and core–shell (silica–gold) nanoparticle. We use a numerical framework based on the finite element method (FEM) to compare energy deposition profiles in these nanoparticles and in their surrounding plasma, by focusing on the impact of the nanoparticle size and the laser fluence. Our calculations show that the maximum energy deposition in plasma occurs in core–shell nanoparticles with a diameter of 130 nm and the ratio of core to shell radius of 0.8 and in solid nanoparticles with a diameter of 170 nm.

A novel and greener approach for shape controlled synthesis of gold and gold–silver core shell nanostructure and their application in optical coatings

Green and facile synthetic methods have gained marvellous fame for the production of polyhedral, anisotropic and spherical gold, and gold–silver bimetallic nanostructures. The useful pivotal characteristics of a green procedure are the usage of environment benign solvent medium, reducing and stabilising agents, and shorter reaction time. We describe here a novel, and greener method for the production of gold and gold–silver core shell nanostructures using aqueous fish scales extract of the Labeo rohita. The effect of various reaction parameters, such as temperature and concentration for the synthesis of the nanostructures were studied. Results indicated that triangular and decahedron gold nanostructures were formed at a lower temperature (40°C) and concentration (10%). While, icosahedral and spherical gold nanostructures were produced at a comparatively higher temperature (100°C) and concentration (40%). The study also revealed that the core–shell bimetallic nanostructures with different morphologies (spherical and oval-shape) were formed at different ratios of chloroaurate and silver nitrate solution. Thus, the present study indicated a simple shape controlled synthesis of gold and gold silver core–shell nanostructures. The synthesised gold nanotriangles were coated over the glass substrate and found to be highly efficient in absorbing infra-red radiations for potential architectural applications. Therefore, the study demonstrated the facile usage of gold nanotriangles for optical coatings. The present strategy depicted the dual functional ability of the fish scale extract as reducing and stabilising agents. This strategy also eliminates the usage of hazardous chemicals, toxic solvents and harsh reducing and stabilizing agents.

Kinetically Controlled Growth of Gold Nanoplates and Nanorods via a One-Step Seed-Mediated Method

In this research, we further developed the one-step seed mediated method to synthesize gold nanoparticles (GNPs) and control their resulting shapes to obtain hexagonal, triangular, rod-shaped, and spherical gold nanostructures. Our method reveals that the reaction kinetics of formation of GNPs with different shapes can be controlled by the rate of addition of ascorbic acid, because this is the critical factor that dictates the energy barrier that needs to be overcome. This in turn affects the growth mechanism process, which involves the adsorption of growth species to gold nanoseeds. There were also observable trends in the dimensions of the GNPs according to different rates of addition of ascorbic acid. We performed further analyses to investigate and confirm the characteristics of the synthesized GNPs.

Real time nanoscale structural evaluation of gold structures on Si (100) surface using in-situ transmission electron microscopy

Transport behavior of gold nanostructures on Si(100) substrate during annealing under high vacuum has been investigated using in-situ real time transmission electron microscopy (TEM). A comparative study has been done on the morphological changes due to annealing under different vacuum environments. Au thin films of thickness ∼2.0 nm were deposited on native oxide covered silicon substrate by using thermal evaporation system. In-situ real time TEM measurements at 850 °C showed the isotropic growth of rectangular/square shaped gold-silicon alloy structures. During the growth, it is observed that the alloying occurs in liquid phase followed by transformation into the rectangular shapes. For similar system, ex-situ annealing in low vacuum (10−2 millibars) at 850 °C showed the spherical gold nanostructures with no Au-Si alloy formation. Under low vacuum annealing conditions, the rate of formation of the oxide layer dominates the oxide desorption rate, resulting in the creation of a barrier layer between Au and Si, which restricts the inter diffusion of Au in to Si. This work demonstrates the important role of interfacial oxide layer on the growth of nanoscale Au-Si alloy structures during the initial growth. The time dependent TEM images are presented to offer a direct insight into the fundamental dynamics of the sintering process at the nanoscale.

Multipole Surface Plasmon Resonance in Electrodeposited Gold Nanoparticles

Electrodeposition is a convenient, economical and template-free tool to create the gold nanostructures. A two-electrode electrochemical process is used for the deposition process. In this method by controlling the deposition time and electrode potential, nearly spherical and rod-like gold nanostructures were synthesized through the reduction of Chlorauric acid with citric acid as a complexing agent. Spherical gold nanostructures of different size around 2 nm to 30 nm and rod-like nanostructures with an aspect ratio 0.5 were grown directly on fluorine-doped tin oxide (FTO)-coated glass substrate. The growth mechanism of gold nanostructures is explained with the help of oriented attachment process. The contact angle measurement showed the hydrophilic nature of gold nanostructures using water with contact angle of about 56°. The optical properties showed a dipole, quadrupole and an octupole plasmon resonance mode at around 625 nm, 530 nm and 422 nm respectively. The dipole resonance peak extends further to give a broad absorption band in the near infrared region of electromagnetic waves. The refractive index sensitivity of gold nanoparticles in various solvents was investigated by calculating the red shift of surface plasmon resonance (SPR) peaks. The quadrupole plasmon resonance mode showed maximum SPR sensitivity as compared to dipole and octupole plasmon resonance mode. The controlled formation of gold nanoparticles with variation of SPR over wide range of visible region supports the potential applications in biosensors, nanoelectronics and plasmon enhanced light absorption in photovoltaics, etc.

Novel two-step synthesis of various gold nanostructures using Langmuir monolayers

Ribbon-like, wedge-shaped, and spherical gold nanostructures were prepared via a novel two-step growth method. Various gold nanostructures were first pre-formed in aqueous solution by using β-cyclodextrin (β-CD) as both reducing and capping agent. Due to the continuous growth of the pre-formed gold nanostructures at the air/water interface with the help of the Langmuir monolayers of 1-hexadecyl-3-methylimidazolium bromide (C 16mimBr), morphology changes can be observed obviously. The gold nanostructures were characterized by transmission electron microscopy (TEM) and UV–vis spectroscopy. A possible mechanism based on the interaction between β-CD and the pre-formed gold nanostructures is proposed.

Analytical Application of Pyramidal, Rodlike, and Spherical Gold Nanostructures: Simultaneous Detection of Ascorbic Acid and Uric Acid

AbstractSimultaneous detection of ascorbic (AA) and uric acid (UA) is developed at pyramidal (NP), rodlike (NR), and spherical (NS) gold nanostructures, due to their high electrocatalytic activities toward the oxidation of AA and UA. Unlike at bare gold electrode, the fouling resulted from the oxidized product of AA is eliminated at the nanostructured gold electrode. The voltammetric signals of AA and UA are completely separated with a potential difference of 216 mV, 158 mV and 195 mV, respectively, at the pyramidal, rodlike, and spherical gold surfaces. The experimental results reveal that solution pH effects the peak separation of AA and UA, acidic solution is more favorable for the simultaneous determination of AA and UA than neutral one, than alkaline one. The coexistence of a large excess of AA does not interfere with the voltammetric sensing of UA, vice versa. All the three kinds of nanostructured gold electrodes show excellent sensitivity, stability, selectivity, low detection limit, quick response and wide linear range in the repeated detection of AA and UA. The practical utility of the present nanostructured gold electrodes is demonstrating by determining the concentration of AA in fruit juice and UA in urine sample.

Pyramidal, Rodlike, Spherical Gold Nanostructures for Direct Electron Transfer of Copper, Zinc-Superoxide Dismutase: Application to Superoxide Anion Biosensors

It is the first time that direct electron transfer of copper, zinc-superoxide dismutase (Cu, Zn-SOD) is realized at nanospherical, nanorodlike, and nanopyramidal gold nanostructures, without any mediators or promoters. Thermodynamic and kinetic parameters of the electron transfer vary with the morphology of the electrodeposited gold nanostructures, suggesting the morphology-dependent electrochemistry of SOD. Experimental results reveal that SOD is strongly confined onto the nanostructured gold surfaces and processes its inherent enzymatic activity after being adsorbed on all three kinds of gold nanostructures, which also enable the direct electron transfer of SOD itself. A combination of the facilitated direct electron transfer and the bifunctional enzymatic catalytic activities of the SOD substantially offers a dual electrochemical approach to determination of O2(*-), in which O2(*-) could be detected both anodically and cathodically. In both the oxidation and reduction regions, the present O2(*-) biosensors display excellent analytical performance, such as wide linear range, low detection limit, quick response time, and good stability and reproducibility, while not being limited by interferences, for instance, uric acid, ascorbic acid, and hydrogen peroxide.

Morphology-Dependent Electrochemistry and Electrocatalytical Activity of Cytochrome c

The morphology-dependent electrochemistry and electrocatalytical activity of cytochrome c (cyt. c) were investigated at pyramidal, rodlike, and spherical gold nanostructures directly electrodeposited onto sputtered gold surfaces. Direct, reversible electron transfer of cyt. c, for the first time, was realized at nanorod-like and nanopyramidal gold surfaces without any mediators or promoters, while no redox reaction was observed at the nanospherical gold electrode. The electrochemical properties of cyt. c vary with the shape of gold nanostructures with respect to the reversibility of electrode reactions, kinetic parameters, the formal potentials (E0'), and charge-transport resistance (Rct), suggesting shape-dependent mechanisms for the electrode reactions of cyt. c. The experimental results manifest that cyt. c was stably immobilized on the nanostructured gold electrodes with different conformational changes of the heme microenvironment. Consequently, not only the electroactivity, but also the inherent biological activity of the immobilized cyt. c strongly depended on the shape of the electrode surfaces. The facilitated electron transfer combined with the intrinsic catalytical activity of cyt. c substantially constructed a third-generation H2O2 biosensor with high selectivity, quick response time, large linear range, and good sensitivity. The electrocatalytical activity of the immobilized cyt. c toward H2O2 was also found to be morphology dependent, and the linear range of H2O2 detection could be tuned by means of employing the nanostructured gold surfaces with different shapes.

Shape-Controlled Electrodeposition of Gold Nanostructures

A one-step, nontemplated, low-cost electrochemical method for the growth of gold nanostructures with different shapes is reported here. It is the first time that nanopyramidal, nanorod-like, and spherical gold nanostructures were fabricated on polycrystalline gold substrates through electrochemical overpotential deposition (OPD) by easily manipulating the deposited potentials and concentrations of HAuCl4. X-ray diffraction and electrochemical analyses revealed that the pyramidal structures are more extensively dominated by (111) facets in comparison with the other nanostructures. The nanopyramids, which have anisotropic structures, exhibited broad extinction over the visible region, most likely due to plasmon resonance. Oxygen reduction activity of a gold electrode with the pyramidal structures was lower than those of the electrodes with the other nanostructures since the activity at the gold (111) surface is lower than that at the (100) and (110) surfaces.