Vicinity Of Gold Nanoparticles Research Articles

Increase of OH radical yields due to the decomposition of hydrogen peroxide by gold nanoparticles under X-ray irradiation.

We elucidate the decomposition mechanism of hydrogen peroxide, which is formed by water radiolysis, by gold nanoparticles (GNPs) under X-ray irradiation. The variations in yields of hydrogen peroxide generated in the presence of GNPs are evaluated using the Ghormley technique. The increase of yields of OH radicals has been quantified using Ampliflu® Red solutions. Almost all hydrogen peroxide generated by irradiation of <25 Gy is decomposed by GNPs, while the yield of OH radicals increases by 1.6 times. The amount of OH radicals thus obtained is almost equivalent to that of the decomposed hydrogen peroxide. The decomposition of hydrogen peroxide is an essential reaction to produce additional OH radicals efficiently in the vicinity of GNPs.

Monte Carlo simulation of free radical production under keV photon irradiation of gold nanoparticle aqueous solution. Part II: Local primary chemical boost

For the past two decades, gold nanoparticles (GNPs) have been investigated as a radiosensitizing agent for radiation therapy. Many theoretical studies have shown that GNPs increase the dose deposition for keV photon irradiation, both at macro and nano-scales, due to a high photon-gold interaction probability. We studied by Monte Carlo simulations the production of radiolysis chemical products (O•H and H2O2) following an ionization event induced by a 20–90 keV photon in a nanoparticle (NP). We focused here on the primary chemical processes occurring around nanoparticles. In the micrometer range, we obtained an excess of chemical species following GNP ionization, as compared to a reference water nanoparticle (WNP) ionization. This difference came from the dominant processes of photon interaction, i.e., Compton for water and photoelectric for gold, which are characterized by different emitted-electron energy spectra. The overproduction of chemical species could be up to 5 times higher for GNP, depending on the photon energy. The mean concentration of chemical species within 100 nm is higher for GNPs compared to WNPs due to Auger electrons when the nanoparticle radius was equal to 5 nm. On the contrary, it was quite comparable when the nanoparticle radius was equal to 50 nm. This reveals that gold Auger-electrons do not necessarily induce a significant boost of chemical species in the vicinity of GNP, as compared to WNP. However, the chance of GNP ionization to occur is larger, due to higher photon-gold interaction probability than that of water, and could result, especially for large GNPs, in accumulation of oxidative stress in its vicinity.

Femtosecond Plasmonic Laser Nanosurgery (fs-PLN) mediated by molecularly targeted gold nanospheres at ultra-low pulse fluences

Plasmonic Laser Nanosurgery (PLN) is a novel photomodification technique that exploits the near-field enhancement of femtosecond (fs) laser pulses in the vicinity of gold nanoparticles. While prior studies have shown the advantages of fs-PLN to modify cells, further reduction in the pulse fluence needed to initiate photomodification is crucial to facilitate deep–tissue treatments. This work presents an in-depth study of fs-PLN at ultra-low pulse fluences using 47 nm gold nanoparticles, conjugated to antibodies that target the epithelial growth factor receptor and excited off-resonance using 760 nm, 270 fs laser pulses at 80 MHz repetition rate. We find that fs-PLN can optoporate cellular membranes with pulse fluences as low as 1.3 mJ/cm2, up to two orders of magnitude lower than those used at lower repetition rates. Our results, corroborated by simulations of free-electron generation by particle photoemission and photoionization of the surrounding water, shed light on the off-resonance fs-PLN mechanism. We suggest that photo-chemical pathways likely drive cellular optoporation and cell damage at these off-resonance, low fluence, and high repetition rate fs-laser pulses, with clusters acting as local concentrators of ROS generation. We believe that the low fluence and highly localized ROS-mediated fs-PLN approach will enable targeted therapeutics and cancer treatment.

Charge-Induced Lattice Compression in Monolayer MoS2

Electron beam or photonic excitation of localized surface plasmon resonances (LSPRs) in gold nanoparticles and their subsequent nonradiative relaxation create a nonuniform charge distribution near the metal–semiconductor interface via hot-electron injection from gold nanoparticles to the monolayer MoS2 conduction band states. These charge domains induce lattice compression in the MoS2 lattice because of the inverse piezoelectric response arising due to the noncentrosymmetric nature of the crystal lattice. Our high-resolution transmission electron microscopy studies reveal that as much as 9–10% biaxial compressive strain is generated in free-standing monolayer MoS2 in the vicinity of gold nanoparticles, which relaxes rapidly within 50 nm from the edge of the gold nanoparticle. The metal interface-induced hot-electron injection via photonic excitation of LSPRs and the resultant lattice distortion also manifest in shifts as well as broadening of A1g(Γ) and E2g1(Γ) Raman modes of the monolayer MoS2 in presenc...

Radio-sensitization efficacy of gold nanoparticles in inhalational nanomedicine and the adverse effect of nano-detachment due to coating inactivation

Gold nanoparticles (GNPs) are an emerging area of interest in radiation therapy due to their unique radio-sensitizing properties. In the literature, the enhancing capability of GNPs is usually quantified using the metric dose enhancement ratio (DER). Traditionally, the focus of the vast majority of studies has always been on intravenous administration of GNPs. However, recent work showed the potential of using GNP inhalation, rather than intravenous injection, to enhance the dose to the lung. Yet, some of these studies are employing simplistic analytical methods to calculate DER and, thus far, there are no detailed computations of the enhancement profiles therein. Moreover, the coating on the GNP surface can be adversely affected by the large gradient of the radiation dose in the immediate vicinity of GNPs, leading to the rupture of ligands and detachment of GNPs from the surface of the membrane, and hence the loss of its efficacy. In this study, a next-generation deterministic code was used to resolve the DER profile at the interface between the septum, air, and surface of GNPs when they are attached and detached. The results show that the large values of DER in conjunction with the developed hot spots are very effective in lung treatment; on the other hand, coating rupture can lead to significant reduction in DER that may reach 64%. Thus, GNPs can be beneficial in inhalational medicine to treat lung cancer, provided that more comprehensive studies on the characteristics of the coating are addressed to maximize the radio-therapeutic benefit of GNPs.

WE-G-BRE-02: Biological Modeling of Gold Nanoparticle Radiosensitization for Proton Therapy

Purpose: The aim of this work is to investigate the radiosensitization effect of gold nanoparticles (GNP) in a proton beam. A computational model was built using the Local Effect Model (LEM) to predict the biological outcome of gold nanoparticle (GNP) sensitization. We present the results using a clinical proton beam, 6MV photon beam and two kilovoltage photon beams. Methods: First, Monte Carlo simulations were carried out using TOPAS (TOol for PArticle Simulation) to obtain the spatial dose distribution in the vicinity of GNPs. The dose distribution was then used as an input for LEM, which predicts dose-response curves for high linear energy transfer radiation using the track structure. The cell survival curves were evaluated for three particle sources (proton beam, MV photon beam and kV photon beam), various treatment depths for each particle source, various GNP uptakes and two different GNP sizes. Results: For proton therapy, the GNP sensitization effect is highly dependent on the treatment depth due to the energy-dependent interaction probability. We predict that if GNPs can be taken up by the cell nucleus, proton therapy can be significantly enhanced. If GNPs are only internalized into the cytoplasm, proton therapy can still be enhanced by GNPs and if GNPs are not internalized into cells, there will be no direct damage to the nucleus. For the same GNP uptake and concentration, the cell survival at 2Gy is reduced by 80% using kilovoltage photons, 50% using protons and only 2% using clinical MV photons. Finally, for the same weight of GNPs taken up by the cells, 10 nm GNPs causes 3 times more damage than 50 nm GNPs. Conclusion: We showed that GNPs have potential to be used to enhance radiation therapy for clinical proton beams.

Enhancement of electrical conductivity, dielectric anisotropy and director relaxation frequency in composites of gold nanoparticle and a weakly polar nematic liquid crystal

We report complex permittivity characteristics in composites of gold nanoparticles (GNP) and a weakly polar nematic liquid crystal possessing a low frequency director relaxation. Differential calorimetric measurements show that the inclusion of GNP has a strong influence on the isotropic–nematic (fluid–orientational fluid) transition temperature as well its first order character in terms of the transition entropy. The absolute value of conductivity increases by two to three orders of magnitude with respect to that for the host liquid crystal and its concentration dependence is demonstrated to be described by the percolation scaling law generally observed in composites of metal particles and polymers. However, the obtained exponent is much smaller, possibly owing to thermal fluctuations present in the fluid-like nematic medium. The activation energy governing the temperature dependence of conductivity is much higher in the nematic than in the isotropic phase. The frequency dependence of the ac conductivity exhibits a critical frequency that is concentration-dependent, but the exponents obtained defy Jonscher's Universal Response principle. A surprising feature is the observation of a substantial increase of not only the principal permittivity values, but their anisotropy as well. These studies also constitute the first report on the influence of GNP on the director relaxation mode of nematics. In contrast to the behaviour of the static permittivity, the dynamics of the system as measured using the director relaxation is seen to become faster with the presence of GNP. We provide an explanation for this antagonistic behaviour in terms of the alignment of the liquid crystal molecules in the vicinity of GNP, and the importance of the weak polarity of the liquid crystals used.

Photoluminescence enhancement of carbon dots by gold nanoparticles conjugated via PAMAM dendrimers

Carbon dots (CDs) have many fascinating fluorescent properties, however, their low quantum yield limits their applications. In this study, the photoluminescence (PL) of CDs in the vicinity of gold nanoparticles (Au NPs) is enhanced significantly due to the surface plasmon resonance (SPR) of the Au NPs. This is achieved by conjugating Au NPs and CDs to dendrimers (PAMAM) through an amidation reaction, resulting in the formation of the Au-PAMAM-CD conjugates. The maximum 62-fold enhancement was obtained with an optimized molar ratio between Au NPs, PAMAM, and CDs. In this process, PAMAM, which serves as a spacer, can keep Au NPs and CDs at an appropriate distance for PL enhancement. The adjustment of the amount of Au NPs or CDs linked to PAMAM can induce the optimum PL enhancement. This strategy can be easily applied to different metal-space-fluorophore systems to enhance the fluorescence of fluorophores.

Gold Nanoparticle Capping Layers: Structure, Dynamics, and Surface Enhancement Measured Using 2D‐IR Spectroscopy

Surface analysis: two-dimensional infrared spectroscopy (2D-IR) was used to probe amide and carboxylate functional groups in the vicinity of gold nanoparticles and their aggregates. The data presented shows that the unique ability of 2D-IR spectroscopy to characterize broadening mechanisms and cross peaks offers new insights into gold nanoparticle capping layer structure and dynamics.

Experimental photophysical characterization of fluorophores in the vicinity of goldnanoparticles

We propose an experimental-based tool for dealing with fluorescence modulation close tonanoparticles for application in studies of fluorophores in the vicinity of gold nanoparticles(AuNPs), typically addressed via theoretical models. We performed a photophysicalcharacterization of fluorophores in the vicinity of AuNPs, showing that correctΦF determination suffers from a local pH effect, and address the observed radiativeenhancement. Our approach is based on the experimental assurance that the referencefluorophores are in the same optical conditions as those of the AuNP–fluorophoreconjugates. We demonstrate the relevance for introducing corrections for the inner filtereffect and the reabsorption of the emitted light caused by AuNPs. The proposed approachcould circumvent the need for theoretical based corrections and allow for moreaccurate determination of fluorescence emission in the vicinity of gold nanoparticles.

Localization of the electromagnetic field in the vicinity of gold nanoparticles: Surface modification of different substrates

Theoretical predictions and experimental results for nanosized modification of metal (Au), semiconductor (Si), or dielectric (soda lime glass) substrates using near-electromagnetic field enhancement in the vicinity of gold nanoparticles are presented. The near field properties for the system consisting of an isolated gold nanoparticle or nanoparticle aggregate deposited on the substrates, which is irradiated by electromagnetic wave, are investigated using Finite Difference Time Domain Simulation technique. The influence of the substrate material on the near field distribution characteristics is predicted. The results reveal that the field on the substrate surface is enhanced in the three investigated cases, but its spatial distribution and magnitude depend on the substrate material. In the case of the metal and semiconductor substrate the enhanced near field is strongly localized in the vicinity of the contact point with the particle, in an area with diameter smaller than the particle's one. The intensity of the enhanced field on the glass is more than an order of magnitude lower than the case of using silicon substrate. The properties of the near field on the substrate surface also depend on the particle arrangement. For a two-dimensional gold nanoparticle array, when the particles are closely arrayed, the intensity of the enhanced field on the substrate surface is minimal. With the increase of the interparticle distance the near field intensity increases. The validity of the obtained theoretical results is confirmed experimentally.

Near field properties in the vicinity of gold nanoparticles placed on various substrates for precise nanostructuring

We present theoretical results on the near field distribution in the vicinity of gold particles excited by laser radiation and placed on various substrate materials. The study is directed towards the precise nanostructuring of different material surfaces. The calculations are performed on the basis of the FDTD simulation technique. Metal (Au), semiconductor (Si) and dielectric (SiO2) substrate materials are investigated. Experimental results are shown to confirm the validity of the obtained FDTD simulation results. The results show that the field in the vicinity of the point of contact is enhanced, and the enhancement factor depends on the substrate material, particle size and the wavelength of the incident optical radiation. The characteristic size of the field enhanced area is found to be several times smaller than the gold particle size: for the case of the smallest particle diameter of 40 nm it is about 10 nm. The enhancement factor of the electric field on the substrate surface is highest when the substrate is gold metal and it decreases about two orders of magnitude when dielectric SiO2 substrate is used. The characteristic penetration depth of the enhanced field is within several tens of nanometres and the depth weakly depends on the substrate material and the laser excitation wavelength. The dependence of the gold particle size on the field enhancement factor is investigated as well. The present results can be used to predict and design precise nanostructuring on different materials with gold nanoparticles excited by a femtosecond laser pulse.

Nanostructuring of silicon surface by femtosecond laser pulse mediated with enhanced near-field of gold nanoparticles

Nanostructure fabrication on a silicon substrate using a near-field electromagnetic enhancement in the vicinity of gold nanoparticles is studied. Experimental and theoretical investigations are made in order to clarify the properties of the nanoholes produced. The obtained results show that this nanofabrication technique is a flexible method for precise surface nanostructuring. Gold particles with diameters of 40, 80, or 200 nm are placed on the silicon substrate by a spin-coating method, and a 100 fs laser pulse (λ=820 nm) is used to irradiate the samples. A theoretical treatment of the results obtained is made by FDTD (finite difference time domain) simulation and calculations of the near field scattering cross section based on Mie’s theory. The effect of the laser fluence, polarization, and particle size and arrangement on the nanohole properties is studied. The nanohole profiles correspond to the field distributions on the substrate in the low laser fluence region. By using a lower laser fluence than the ablation threshold of bulk silicon, a hole with a diameter of about 40 nm can be produced using a 200 nm gold particle. Furthermore, the gold particles exhibit a considerable field enchantment even at gold particle sizes of a few tens of nanometers, which offers a good opportunity for further decreases in the size of the produced structures. A highest electric field enhancement factor of about 26 is obtained for particles with a diameter of 200 nm. With the decrease of the particle size the field enhancement also decreases. Particle arrangement on the substrate surface strongly affects both the electric field distribution and the enhancement effect of the particles. The highest enhancement for a particle pair is obtained when the polarization of the incident radiation is parallel to the pair axis (longitudinal mode). A good correlation is obtained between the near-field distribution predicted by FDTD simulation and the parameters of the experimentally produced nanoholes.

Nanoparticle-based optical biosensors for the direct detection of organophosphate chemical warfare agents and pesticides

Neurotoxic organophosphates (OP) have found widespread use in the environment for insect control. In addition, there is the increasing threat of use of OP based chemical warfare agents in both ground based warfare and terrorist attacks. Together, these trends necessitate the development of simple and specific methods for discriminative detection of ultra low quantities of OP neurotoxins. In our previous investigations a new biosensor for the direct detection of organophosphorus neurotoxins was pioneered. In this system, the enzymatic hydrolysis of OP neurotoxins by organophosphate hydrolase (OPH) generated two protons in each hydrolytic turnover through reactions in which P–X bonds are cleaved. The sensitivity of this biosensor was limited due to the potentiometric method of detection. Recently, it was reported that a change in fluorescence properties of a fluorophore in the vicinity of gold nanoparticles might be used for detection of nanomolar concentrations of DNA oligonucleotides. The detection strategy was based on the fact that an enhancement or quenching of fluorescence intensity is a function of the distances between the gold nanoparticle and fluorophore. While these reports have demonstrated the use of nanoparticle-based sensors for the detection of target DNA, we observed that the specificity of enzyme–substrate interactions could be exploited in similar systems. To test the feasibility of this approach, OPH-gold nanoparticle conjugates were prepared, then incubated with a fluorescent enzyme inhibitor or decoy. The fluorescence intensity of the decoy was sensitive to the proximity of the gold nanoparticle, and thus could be used to indicate that the decoy was bound to the OPH. Then different paraoxon concentrations were introduced to the OPH–nanoparticle–conjugate–decoy mixtures, and normalized ratio of fluorescence intensities were measured. The greatest sensitivity to paraoxon was obtained when decoys and OPH–gold nanoparticle conjugates were present at near equimolar levels. The change in fluorescence intensity was correlated with concentration of paraoxon presented in the solution.