Interface Of Gold Nanoparticles Research Articles

Analysis of magnetic field impact on nanoparticles used in nanomedicine and a measurement approach

Nanomedicine, in particular the use nanoparticles for drug delivery (DD), is an increasing field of development and advancement. The influence and the interference of magnetic field about delivery action is an important field of investigation. Vaccines and specific drugs for known and rare pathologies can get benefits from this approach. The main goal of the work is to provide a modelling that can support the know-how of the impact of a magnetic field about the delivery of drug allocated on Nanoparticles (NPs), thus defining guidelines to measure the delivery function for generic biocompatible NPs. In particular, by means of Finite Element Method (FEM) approach, the impact magnetic field, on gold nanoparticle (GN), used in nanomedicine for DD process, is analysed to facilitate the knowledge of the delivery mechanisms. The study is addressed to the estimation of the magnetic field distribution on the GNs interface, supporting the efficacy of the magnetic field stimulation. The paper is concluded by discussing measurement approaches useful to define guidelines. The main goal of the paper is to provide a methodology to understand DD phenomena in nanotechnology using a magnetic field as stimuli, by defining at the same time tools and approaches tailoring a measurement protocol in nanotechnology.

A Study of the Interface of Gold Nanoparticles Conjugated to Cowpea Fe-Superoxide Dismutase.

The iron superoxide dismutase (FeSOD) is a first barrier to defend photosynthetic organisms from superoxide radicals. Although it is broadly present in plants and bacteria, FeSODs are absent in animals. They belong to the same phylogenic family as Mn-containing SODs, which are also highly efficient at detoxifying superoxide radicals. In addition, SODs can react with peroxynitrite, and FeSOD enzyme has already been used to evaluate the anti-nitrative capacity of plant antioxidants. Gold nanoparticles (AuNPs) have been shown to significantly improve the functionality and the efficiency of ligands, providing they are properly assembled. In this work, the characteristics of the recombinant cowpea (Vigna unguiculata) FeSOD (rVuFeSOD) immobilized onto AuNPs were investigated as a function of (1) NP surface chemistry and (2) biofunctionalization methods, either physical adsorption or covalent bonding. The NP surface chemistry was studied by varying the concentration of the ligand molecule 11-mercaptoundecanoic acid (MUA) on the NP surface. The coverage and activity of the protein on AuNPs was determined and correlated to the surface chemistry and the two biofunctionalization methods. rVuFeSOD-AuNPs conjugate stability was monitored through absorption measurements, agarose gel electrophoresis and DLS, enzymatic activity by a colorimetric assay and by in-gel activity assay, and coverage was measured by colorimetric assay. When using physical adsorption, the NP is the most perturbing agent for the activity of the enzyme. In contrast, only the NP coverage was affected by MUA ligand concentration. However, during covalent attachment, both the NP and the concentration of MUA on the surface influenced the enzyme activity, while the coverage of the NP remained constant. The results evidence the importance of the biomolecule and AuNP interaction for the functionality of the hybrid. These strategies can be used to develop electrochemical biosensors for O2•- and for peroxynitrite in biomedical applications.

Ultrafast electron transfer at the interface of gold nanoparticles and methylene blue molecular adsorbates.

Due to their unique property of possessing localized surface plasmon resonance (LSPR), metal nanoparticles (MNPs) have drastically impacted many applications. For instance, local field enhancement through LSPRs and plasmonic hot electron transfer are known to enhance the efficiency of MNP-based photoreactions. Here, we report on the ultrafast electron transfer from gold nanoparticles (Au-NPs) to methylene blue (MB) molecular adsorbate using femtosecond pump-probe and steady-state absorption and emission spectroscopy techniques. Although the energy band alignment of the interface allows both dipole-dipole Förster resonance energy transfer (FRET) and charge transfer, because the MB emission intensity at the Au-NPs/MB nanocomposite decreased by a factor of ∼3.6, the FRET process was ruled out. Selective excitation of LSPRs at the Au-NPs/MB nanocomposite sample in pump-probe experiments led to the formation of the MB ground-state depletion and a positive induced absorption at wavelengths shorter than ∼500 nm, which was attributed to the shoulder of the MB- anion absorption. Furthermore, despite the fact that the concentration of Au-NPs in the nanocomposite sample is the same as that in the Au-NPs solution, the initial intensity of the LSPR depletion signal was about six times weaker than that in the Au-NPs sample. These observations suggest that electron transfer from excited Au-NPs to MB adsorbates took place on a time-scale that is shorter than the ∼50 fs experimental temporal resolution.

Strong metal-support interaction boosting the catalytic activity of Au/TiO2 in chemoselective hydrogenation

Gold catalysts have been reported as highly effective catalysts in various oxidation reactions. However, for chemoselective hydrogenation reactions, gold-based catalysts normally show much lower catalytic activity than platinum group metals, even though their selectivities are excellent. Here, we report that the chemoselective hydrogenation activity of 3-nitrostyrene to 3-vinylaniline over Au/TiO2 can be enhanced up to 3.3 times through the hydrogen reduction strategy. It is revealed that strong metal-support interaction, between gold nanoparticles (NPs) and TiO2 support, is introduced through hydrogen reduction, resulting in partial dispersion of reduced TiOx on the Au surface. The partially covered Au not only increases the perimeter of the interface between the gold NPs and the support, but also benefits H2 activation. Reaction kinetic analysis and H2-D2 exchange reaction show that H2 activation is the critical step in the hydrogenation of 3-nitrostyrene to 3-vinylaniline. Density functional theory calculations verify that hydrogen dissociation and hydrogen transfer are favored at the interface of gold NPs and TiO2 over the hydrogen-reduced Au/TiO2. This study provides insights for fabricating highly active gold-based catalysts for chemoselective hydrogenation reactions.

Ultrasensitive evaluation of Ribonuclease H activity using a DNAzyme-powered on-particle DNA walker

The evaluation of Ribonuclease H (RNase H) activity is very important for anti-HIV drug development and the study of cellular processes, including DNA replication, DNA repair and transcription. However, the highly sensitive detection of RNase H activity with a simple strategy remains challenging. Here, a DNAzyme-powered on-particle DNA walker was proposed as a signal amplifier to evaluate the RNase H activity at levels as low as 0.00847 U mL−1. Pre-caged enzyme strands and substrate strands of Mn2+-specific DNAzyme were modified at the interface of gold nanoparticles, forming the DNA walker probes. In the absence of RNase H, a minimum fluorescent signal was observed due to excellent ability of gold nanoparticles to quench the fluorophore that labeled the substrate strand. In the presence of RNase H, the DNA/RNA hybrid complex was hydrolyzed to release single stranded DNA, which was able to hybridize to the locker strand that caged the enzyme strand. Following the addition of Mn2+, the active forms of DNAzymes were cleaved at the RNA site of substrate strands, releasing enhanced fluorescent molecules. Finally, the walker strands traveled over the AuNPs like a machine to amplify the signal, thus indirectly measuring the activity of RNase H. This approach proved to be an ultrasensitive and simple method for the evaluation of RNase H activity in cell extracts and has also been successfully used to evaluate the effects of inhibitors.

Catalytic hairpin assembly-assisted lateral flow assay for visual determination of microRNA-21 using gold nanoparticles.

The authors describe an improved lateral flow assay based on (a) the use of catalytic hairpin assembly (CHA), and (b) on signal amplification performed at the interface of gold nanoparticles (AuNPs). The combination of the amplification capability of the CHA reaction and the unique optical properties of AuNPs results in an assay that has a sensitivity that is improved by more than two orders of magnitude. MicroRNA-21 was employed as a model analyte to prove the concept. The presence of microRNA-21 triggers the self-assembly of two hairpin DNAs into double stranded DNA and exposing biotin molecules on the surface of AuNPs. Hence, the target becomes recycled and the signal is strongly amplified. The AuNPs carrying biotin are captured on the test line of the strip to display a red zone. This enables the visual recognition of microRNA without the need for any instrumentation. The fast quantitation of microRNA via the red band intensity is accomplished with the help of software, and the limit of detection is 0.89 pM. The enhanced lateral flow assay was employed to the determination of microRNA-21 in cell extracts and spiked serum samples. Graphical abstract A lateral flow assay for microRNAis described with a detection limit that is improved by two orders of magnitude. It is based on catalytic hairpin assembly (CHA) signal amplification performed at the interface of gold nanoparticles.

Atomic-Scale Explanation of O2 Activation at the Au-TiO2 Interface.

By a combination of electron paramagnetic resonance spectroscopy, finite-temperature ab initio simulations, and electronic structure analyses, the activation of molecular dioxygen at the interface of gold nanoparticles and titania in Au/TiO2 catalysts is explained at the atomic scale by tracing processes down to the molecular orbital picture. Direct evidence is provided that excess electrons in TiO2, for example created by photoexcitation of the semiconductor, migrate to the gold particles and from there to oxygen molecules adsorbed at gold/titania perimeter sites. Superoxide species are formed more efficiently in this way than on the bare TiO2 surface. This catalytic effect of the gold nanoparticles is attributed to a weakening of the internal O-O bond, leading to a preferential splitting of the molecule at shorter bond lengths together with a 70% decrease of the dissociation free energy barrier compared to the non-catalyzed case on bare TiO2. The findings are an important step forward in the clarification of the role of gold in (photo)catalytic processes.

ChemInform Abstract: Maleimide‐Modified Gold Nanoparticles (AuNPs): A Versatile Platform for Interfacial Click Reactions Leading to Chemically Modified AuNPs

AbstractReview: [30 refs.

Maleimide-Modified Gold Nanoparticles (AuNPs): A Versatile ­Platform for Interfacial Click Reactions Leading to Chemically Modified AuNPs

The maleimide moiety can undergo a wide variety of organic reactions, including Diels–Alder reactions, dipolar cycloadditions, and Michael-type additions, making it a suitable moiety for further elaboration of the functionality at the interface of gold nanoparticles (AuNPs) through key reactions that are useful in a host of applications. This account will cover: (1) our approach to prepare maleimide-AuNPs, (2) our survey of the scope of the reactivity of organic-solvent-soluble maleimide-AuNPs, which are very slow, impractical, and required the development of high-pressure techniques in AuNP chemistry yielding dramatic results, and (3) the extension of these ideas to prepare water-soluble small AuNPs to expand the scope of the organic transformation to aqueous environments. Within each of these sections there were challenges that had to be overcome, and we will describe the evolution of the ideas so that readers can get a glimpse of our thinking and problem solving as we proceeded. 1 Introduction 2 Maleimide-AuNPs: The Synthetic Strategy 3 Reactivity of the Organic-Solvent-Soluble Maleimide-AuNP Template 4 Synthesis of the Water-Soluble Maleimide-AuNP Template 5 Reactivity of the Water-Soluble Maleimide-AuNP Template 6 Concluding Remarks

An Azide-Functionalized Nitronyl Nitroxide Radical: Synthesis, Characterization and Staudinger–Bertozzi Ligation Reactivity

An azide-functionalized nitronyl nitroxide was synthesized and its reactivity towards the Staudinger–Bertozzi ligation was explored. Whereas a model reaction in solution showed the conversion of nitronyl nitroxide to an imino nitroxide radical, the same reaction at the interface of gold nanoparticles allowed for successful covalent incorporation of the nitronyl nitroxide radical onto the nanoparticles.

2P062 金ナノ粒子の界面におけるアミロイド線維形成機構に関する研究(01C. 蛋白質:物性,ポスター,第52回日本生物物理学会年会(2014年度))

2P062 金ナノ粒子の界面におけるアミロイド線維形成機構に関する研究(01C. 蛋白質:物性,ポスター,第52回日本生物物理学会年会(2014年度))

Molecular Adsorption and Resonance Coupling at the Colloidal Gold Nanoparticle Interface

Second harmonic generation is used to investigate the adsorption properties of malachite green, brilliant green, and methyl green to the surface of 80 nm colloidal gold nanoparticles capped with mercaptosuccinic acid in water. The experimental results are fit using the modified Langmuir model to obtain the free energies of adsorption and the adsorbate site densities for each cationic triphenylmethane molecular dye. Malachite green is observed to bind more strongly than brilliant green or methyl green to the nanoparticle surface but has a lower adsorbate site density, indicating differences in image-charge effects, adsorbate–adsorbate repulsions, and adsorption tilt angles. Complementary measurements from extinction spectroscopy show plasmonic and molecular resonance coupling leading to the formation of new polaritonic states and Fano-type resonances with corresponding plasmon and molecular spectral depletions as the adsorbate concentration is increased. The changes in the resonance coupling spectra are co...

Microfabricated Gas Chromatograph for On-Site Determination of Trichloroethylene in Indoor Air Arising from Vapor Intrusion. 1. Field Evaluation

Results are presented of inaugural field tests of two identical prototype microfabricated gas chromatographs (μGC) adapted for the in situ determination of trichloroethylene (TCE) in indoor air in support of vapor intrusion (VI) investigations. Each μGC prototype has a pretrap and partially selective high-volume sampler of conventional design, a micromachined-Si focuser for injection, dual micromachined-Si columns for separation, and an integrated array of four microscale chemiresistors with functionalized gold nanoparticle interface films for multichannel detection. Scrubbed ambient air is used as the carrier gas. Field-generated calibration curves were linear for injected TCE masses of 26-414 ng (4.8-77 ppb·L; r(2) > 0.98) and the projected single-sensor detection limit was 0.052 ppb for an 8-L air sample collected and analyzed in 20 min. Consistent performance between the prototypes and good medium-term stability were shown. Above the mitigation action level (MAL) of 2.3 ppb for the field-test site, μGC TCE determinations fell within ±25% of those from the reference method for 21 of 26 measurements, in the presence of up to 37 documented background VOCs. Below the MAL, positive biases were consistently observed, which are attributable to background VOCs that were unresolvable chromatographically or by analysis of the sensor-array response patterns. Results demonstrate that this type of μGC instrument could serve the need for routine TCE determinations in VI-related assessment and mitigation efforts.

Probing the colloidal gold nanoparticle/aqueous interface with second harmonic generation

The interface of 16 nm colloidal gold nanoparticles with the aqueous solution in which they are suspended is investigated using second harmonic generation. The population of malachite green freely adsorbing to the gold nanoparticle interface as a function of concentration is obtained. The experimental results are in good agreement with the modified Langmuir model, which includes depletion of the adsorbate bulk concentration. The free energy of adsorption is determined to be −15.4 ± 0.4 kcal/mol with 1.13 ± 0.04 × 10 3 sites per nanoparticle. These results provide the first direct measurement of the isotherm of molecules adsorbing to colloidal metallic nanoparticles.

Densely integrated array of chemiresistor vapor sensors with electron-beam patterned monolayer-protected gold nanoparticle interface films

Use of electron-beam induced crosslinking to pattern films of monolayer-protected gold nanoparticles (MPNs) onto a chemiresistor (CR) sensor array is described. Each of the four CRs comprises a 100 µm(2) set of interdigital electrodes (IDEs) with 100 nm widths and spaces, separated from adjacent devices by 4 µm. Films of four MPNs, each with a different thiolate monolayer, were successively patterned on the IDEs. Vapor exposures yield rapid, reversible changes in CR resistances and differential vapor sensitivities comparable to those reported for larger CRs with unpatterned MPN films. The array response patterns facilitate vapor discrimination. This is the smallest MPN-coated CR array yet reported. The advantages of using such an array as the detector in microfabricated gas chromatographic analyzers are considered.

Rapid identification and high sensitive detection of cancer cells on the gold nanoparticle interface by combined contact angle and electrochemical measurements

In this study, we have proposed a novel strategy for the rapid identification and high sensitive detection of different kinds of cancer cells by means of electrochemical and contact angle measurements. A simple, unlabeled method based on the functionalized Au nanoparticles (GNPs) modified interface has been utilized to distinguish the different cancer cells, including lung cancer cells, liver cancer cells, drug sensitive leukemia K562/B.W cells and drug resistant leukemia K562/ADM cells. The relevant results indicate that under optimal conditions, this method can provide the quantitative determination of cancer cells, with a detection limit of ∼10 3 cells mL −1. Our observations demonstrate that the difference in the hydrophilic properties for target cellular surfaces and in the uptake efficiency of the anticancer drug daunorubicin for different cancer cells could be readily chosen as the elements of cancer identification and sensitive detection. This raises the possibility to advance the promising clinic diagnosis and monitoring of tumors with the aim of successful chemotherapy of human cancers.