Catalytic Gold Nanoparticles Research Articles

Ultrasensitive colorimetric detection of NF-κB protein at picomolar levels using target-induced passivation of nanoparticles.

We developed a highly sensitive and selective sensor based on the nanoprobe conjugates of catalytic nanoparticles and double-stranded DNA (dsDNA) for the colorimetric detection of NF-κB protein. The sensing mechanism takes advantage of the catalytic activity of nanoparticle surfaces and the specific binding of NF-κB to a dsDNA sequence. In the presence of NF-κB, the highly selective interactions between dsDNA and NF-κB lead to the passivation of the catalytic nanoparticle surfaces, impeding the sodium borohydride-mediated reduction rate of 4-nitrophenol. The correlation between the NF-κB concentration and the visualized reduction rate of 4-nitrophenol from yellow to colorless clearly demonstrates the highly quantitative nature of the sensor. Importantly, this sensor can conclusively detect concentrations as low as 6.39 pM of NF-κB, which to best of our knowledge is the lowest limit of detection for a colorimetric NF-κB detection system. The excellent sensitivity of this sensor relies on the high binding constant of NF-κB to dsDNA and the catalytic activity of nanoparticle surfaces for the signal amplification. This sensor allows visual detection without the need for any spectrometric instrumentation. We also determined the various parameters such as the pH, temperature, incubation time, and salt concentration for optimal NF-κB-dsDNA interactions. Finally, we demonstrated the performance of the sensor with simulated sample analysis. Graphical abstract A highly sensitive and selective colorimetric detection of protein NF-κB using the nanoprobeconjugates of catalytic gold nanoparticles and double-stranded DNA (dsDNA) has been developed.

Observation and Identification of an Atomic Oxygen Structure on Catalytic Gold Nanoparticles

AbstractInteractions between oxygen and gold surfaces are fundamentally important in diverse areas of science and technology. In this work, an oxygen dimer structure was observed and identified on gold nanoparticles in catalytic decomposition of hydrogen peroxide to oxygen and water. This structure, which is different from isolated atomic or molecular oxygen surface structures, was observed with in situ surface‐enhanced Raman spectroscopic measurements and identified with density functional theory calculations. The experimental measurements were performed using monodisperse 5, 50 and 400 nm gold particles supported on silica with liquid‐phase hydrogen and deuterium peroxides at multiple pH values. The calculations show that on surfaces with coordinatively unsaturated gold atoms, two oxygen atoms preferentially share a gold atom with a bond distance of 0.194–0.196 nm and additionally bind to two other surface gold atoms with a larger bond distance of 0.203–0.213 nm, forming an Au‐O‐Au‐O‐Au structure. The formation of this structure depends on reaction rates and conditions.

Observation and Identification of an Atomic Oxygen Structure on Catalytic Gold Nanoparticles.

Interactions between oxygen and gold surfaces are fundamentally important in diverse areas of science and technology. In this work, an oxygen dimer structure was observed and identified on gold nanoparticles in catalytic decomposition of hydrogen peroxide to oxygen and water. This structure, which is different from isolated atomic or molecular oxygen surface structures, was observed with in situ surface-enhanced Raman spectroscopic measurements and identified with density functional theory calculations. The experimental measurements were performed using monodisperse 5, 50 and 400 nm gold particles supported on silica with liquid-phase hydrogen and deuterium peroxides at multiple pH values. The calculations show that on surfaces with coordinatively unsaturated gold atoms, two oxygen atoms preferentially share a gold atom with a bond distance of 0.194-0.196 nm and additionally bind to two other surface gold atoms with a larger bond distance of 0.203-0.213 nm, forming an Au-O-Au-O-Au structure. The formation of this structure depends on reaction rates and conditions.

Partial Reduction and Selective Transfer of Hydrogen Chloride on Catalytic Gold Nanoparticles.

HCl in solution accepts electron density from Au NPs and partially reduces at room temperature, as occurs with other simple diatomic molecules, such as O2 and H2 . The activation can be run catalytically in the presence of alkynes to give exclusively E-vinyl chlorides, after the regio- and stereoselective transfer of HCl. Based also on this method, vinyl chloride monomer (VCM) can be produced in a milder and greener way than current industrial processes.

Partial Reduction and Selective Transfer of Hydrogen Chloride on Catalytic Gold Nanoparticles

AbstractHCl in solution accepts electron density from Au NPs and partially reduces at room temperature, as occurs with other simple diatomic molecules, such as O2 and H2. The activation can be run catalytically in the presence of alkynes to give exclusively E‐vinyl chlorides, after the regio‐ and stereoselective transfer of HCl. Based also on this method, vinyl chloride monomer (VCM) can be produced in a milder and greener way than current industrial processes.

A surface enhanced Raman scattering quantitative analytical platform for detection of trace Cu coupled the catalytic reaction and gold nanoparticle aggregation with label-free Victoria blue B molecular probe

With development of economy and society, there is an urgent need to develop convenient and sensitive methods for detection of Cu2+ pollution in water. In this article, a simple and sensitive SERS sensor was proposed to quantitative analysis of trace Cu2+ in water. The SERS sensor platform was prepared a common gold nanoparticle (AuNP)-SiO2 sol substrate platform by adsorbing HSA, coupling with the catalytic reaction of Cu2+-ascorbic acid (H2A)-dissolved oxygen, and using label-free Victoria blue B (VBB) as SERS molecular probes. The SERS sensor platform response to the AuNP aggregations by hydroxyl radicals (•OH) oxidizing from the Cu2+ catalytic reaction, which caused the SERS signal enhancement. Therefore, by monitoring the increase of SERS signal, Cu2+ in water can be determined accurately. The results show that the SERS sensor platforms owns a linear response with a range from 0.025 to 25μmol/L Cu2+, and with a detection limit of 0.008μmol/L. In addition, the SERS method demonstrated good specificity for Cu2+, which can determined accurately trace Cu2+ in water samples, and good recovery and accuracy are obtained for the water samples. With its high selectivity and good accuracy, the sensitive SERS quantitative analysis method is expected to be a promising candidate for determining copper ions in environmental monitoring and food safety.

Anchoring and promotion effects of metal oxides on silica supported catalytic gold nanoparticles

The understanding of the interactions between the different components of supported metal doped gold catalysts is of crucial importance for selecting and designing efficient gold catalysts for reactions such as CO oxidation. To progress in this direction, a unique supported nano gold catalyst Au/SS was prepared, and three doped samples (Au/SS@M) were elaborated. The samples before and after test were characterized by Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS). It is found that the doping metal species prefer to be located on the surface of gold nanoparticles and that a small amount of additional reductive metal leads to more efficient reaction. During the catalytic test, the nano-structure of the metal species transforms depending on its chemical nature. This study allows one to identify and address the contribution of each metal on the CO reaction in regard to oxidative species of gold, silica and dopants. Metal doping leads to different exposure of interface sites between Au and metal oxide, which is one of the key factors for the change of the catalytic activity. The metal oxides help the activation of oxygen by two actions: mobility inside the metal bulk and transfer of water species onto of gold nanoparticles.

Formation and Catalysis of Gold Nanoparticles Generated through the Physical Mixing of AuCl(PPh3) and Oxides

AuCl(PPh 3 ) was mixed with various kinds of inorganic supports with a mortar. Thermal treatment of the mixture resulted in the formation of gold nanoparticles, particularly when NaY zeolite and CeO 2 were employed as the supports for gold. Catalytic performance in the aerobic oxidation of benzyl alcohol was in good correlation with the degree of the dispersion of gold.

Sequence-Dependent Structure/Function Relationships of Catalytic Peptide-Enabled Gold Nanoparticles Generated under Ambient Synthetic Conditions.

Peptide-enabled nanoparticle (NP) synthesis routes can create and/or assemble functional nanomaterials under environmentally friendly conditions, with properties dictated by complex interactions at the biotic/abiotic interface. Manipulation of this interface through sequence modification can provide the capability for material properties to be tailored to create enhanced materials for energy, catalysis, and sensing applications. Fully realizing the potential of these materials requires a comprehensive understanding of sequence-dependent structure/function relationships that is presently lacking. In this work, the atomic-scale structures of a series of peptide-capped Au NPs are determined using a combination of atomic pair distribution function analysis of high-energy X-ray diffraction data and advanced molecular dynamics (MD) simulations. The Au NPs produced with different peptide sequences exhibit varying degrees of catalytic activity for the exemplar reaction 4-nitrophenol reduction. The experimentally derived atomic-scale NP configurations reveal sequence-dependent differences in structural order at the NP surface. Replica exchange with solute-tempering MD simulations are then used to predict the morphology of the peptide overlayer on these Au NPs and identify factors determining the structure/catalytic properties relationship. We show that the amount of exposed Au surface, the underlying surface structural disorder, and the interaction strength of the peptide with the Au surface all influence catalytic performance. A simplified computational prediction of catalytic performance is developed that can potentially serve as a screening tool for future studies. Our approach provides a platform for broadening the analysis of catalytic peptide-enabled metallic NP systems, potentially allowing for the development of rational design rules for property enhancement.

Colorimetric detection of human chorionic gonadotropin using catalytic gold nanoparticles and a peptide aptamer.

We combined catalytic gold nanoparticles (AuNPs) with an hCG-specific peptide aptamer to create a simple, sensitive, label-free colorimetric assay for hCG. The applications of this colorimetric biosensor may be expanded by changing the peptide aptamer.

Thiol anchoring and catalysis of gold nanoparticles at the liquid interface of thin-organic film-modified electrodes

The deposition of in-situ formed gold nanoparticles at the liquid/liquid (L/L) interface is studied by means of thin-organic-film-modified electrodes (TFE). The degree of ordering and aggregation of gold nanoparticles can be tuned by adding a lipophilic and hydrophilic thiol in the organic and aqueous phase, respectively. The ordered thiol-anchored gold nanoparticles exhibit pronounced catalytic effect toward electron-transfer reactions across the L/L interface.

Catalytic gold nanoparticles immobilized on yeast: From biosorption to bioreduction

In this study, gold nanoparticles (AuNPs) were biologically synthesized and bound to the cell surface of yeast Pichia pastoris (P. pastoris), which exhibited high affinity for Au(III) species in aqueous solution. With the assistance of TEM, FTIR and XRD, the biosynthesis of the AuNPs was investigated by chemical modification of the cell surface, KBr desorption of Au(III) species from the cell surface, and reduction of Au(III) species with mannocarolose extracted from the yeast. Furthermore, the results showed that [AuCl4]− ions were rapidly absorbed and reduced into Au(I) ions by NH2, OH, and other functional groups on the cell surface. Further, the Au(I) ions were reduced into Au(0) to form AuNPs immobilized on the cells. Mannocarolose played an important role in the reduction process. And the catalytic application of AuNPs/P. pastoris to the reduction of 4-nitrophenol was studied. Two other catalysts were prepared by introducing an extraneous reductant to clarify the importance of the AuNPs-yeast involvement in the reduction of 4-nitrophenol. The AuNPs/P. pastoris composites exhibited the best catalytic activity, and their catalytic activity can remain stable even after several rounds of reuse. This work demonstrates the fabrication of a catalyst, through the immobilization of AuNPs onto yeast by extending biosorption to biosynthesis, thus highlighting their potential application as environmentally benign catalysts.

Pattern Recognition Analysis of Proteins Using DNA‐Decorated Catalytic Gold Nanoparticles

A label-free protein analysis strategy is based on patterns of gold nanoparticle (AuNP) growth. AuNPs pretreated with different oligonucleotides are challenged with various proteins. After Au reduction, the colorimetric patterns are processed with linear discriminant analysis. This method discriminates different proteins, or one protein of different concentrations, in mixed samples or even serum and urine.

Fluorescent sensing of mercury(ii) based on formation of catalytic gold nanoparticles

A fluorescence assay for the highly sensitive and selective detection of Hg(2+) using a gold nanoparticle (AuNP)-based probe was proposed. The assay was based on the formation of Hg-Au alloys, which accelerated the oxidization of o-phenylenediamine by dissolved oxygen to produce 2,3-diaminophenazine, a fluorescent product.

Influence of catalytic gold and silver metal nanoparticles on structural, optical, and vibrational properties of silicon nanowires synthesized by metal-assisted chemical etching

We report on the structural and vibrational characterization of silicon (Si) nanowire arrays synthesized by metal-assisted chemical etching (MACE) of Si deposited with metal nanoparticles. Gold (Au) and silver (Ag) metal nanoparticles were synthesized by glancing angle deposition, and MACE was performed in a mixture of H2O2 and HF solution. We studied the structural differences between Au and Ag-etched Si nanowires. The morphology of the synthesized nanowires was characterized by scanning electron microscopy and transmission electron microscopy. The optical and vibrational properties of the Si nanostructures were studied by photoluminescence and Raman spectroscopy using three different excitation sources (UV, visible, and near-infrared) and are correlated to their microstructures. The structural differences between Au-etched and Ag-etched nanowires are due to the higher degree of hole injection by the Au nanoparticle and diffusion into the Si nanowires, causing enhanced Si etching by HF on the nanowire surface. Au-etched nanowires were observed to be mesoporous throughout the nanowire while Ag-etched nanowires consisted of a thin porous layer around the crystalline core. In addition, the surface-enhanced resonant Raman scattering observed is attributed to the presence of the sunken metal nanoparticles. Such Si nanostructures may be useful for a wide range of applications such as photovoltaic and biological and chemical sensing.

Experimental and theoretical study on the synthesis of gold nanoparticles using ceftriaxone as a stabilizing reagent for and its catalysis for dopamine

Electrochemical synthesis of gold nanoparticles on the surface of glassy carbon electrode and preparation of GNPs in aqueous solution using ceftriaxone as an innocuous stabilizing reagent were proposed. The gold nanoparticles were characterized by scanning electron microscopy, transmission electron microscopy, infrared spectrometry, UV spectrophotometry, powder X-ray diffraction, and cyclic voltammetry. The catalysis of gold nanoparticles on the glassy carbon electrode for dopamine was demonstrated. The results indicate that the modified electrode has an excellent repeatability and reproducibility. The relationship between the molecular structure and the dispersion of GNPs on the surface of GCE as well as the catalysis of GNPs for dopamine was discussed.

On the Effect of Atomic Structure on the Activity and Deactivation of Catalytic Gold Nanoparticles

AbstractWe present studies of the structure and stability of catalytic gold nanoparticles through in situ aberration‐corrected electron microscopy to investigate the effect of heating on the nature of the identified atomic active sites. Low coordination surface atoms are replaced by atomically clean surface facets through local rearrangements to minimise surface energy. The associated movement of surface atoms is proposed to directly precede Ostwald ripening. Expansive surface strain resulting from inherently strained structures, such as the decahedra, is shown to diminish with increasing particle size and the associated elastic energy is reduced through a shifting of the disclination axis towards the particle surface. At elevated temperatures a reduction in surface energy anisotropy may lead to energetically favourable morphologies with minimal intrinsic strain. Such processes will act as structural deactivation mechanisms, resulting in a loss of active sites without any necessary associated loss of surface area or change in particle size through traditional sintering mechanisms. Considerations of the active site stability and the particle size according to the reaction conditions are described.

Catalytic gold nanoparticles for fluorescent detection of mercury(II) and lead(II) ions

In this study, we developed a fluorescence assay for the highly sensitive and selective detection of Hg2+ and Pb2+ ions using a gold nanoparticle (Au NP)-based probe. The Hg–Au and Pb–Au alloys that formed on the Au NP surfaces allowed the Au NPs to exhibit peroxidase-mimicking catalytic activity in the H2O2-mediated oxidation of Amplex UltraRed (AUR). The fluorescence of the AUR oxidation product increased upon increasing the concentration of either Hg2+ or Pb2+ ions. By controlling the pH values of 5mM tris–acetate buffers at 7.0 and 9.0, this H2O2–AUR–Au NP probe detected Hg2+ and Pb2+ ions, respectively, both with limits of detection (signal-to-noise ratio: 3) of 4.0nM. The fluorescence intensity of the AUR oxidation product was proportional to the concentrations of Hg2+ and Pb2+ ions over ranges 0.05–1μM (R2=0.993) and 0.05–5μM (R2=0.996), respectively. The H2O2–AUR–Au NP probe was highly selective for Hg2+ (>100-fold) and Pb2+ (>300-fold) ions in the presence of other tested metal ions. We validated the practicality of this simple, selective, and sensitive H2O2–AUR–Au NP probe through determination of the concentrations of Hg2+ and Pb2+ ions in a lake water sample and of Pb2+ ions in a blood sample. To the best of our knowledge, this system is the first example of Au NPs being used as enzyme-mimics for the fluorescence detection of Hg2+ and Pb2+ ions.

On the effect of atomic structure on the deactivation of catalytic gold nanoparticles

Here we present atomic scale studies into the nature of both the internal structure and external surfaces of catalytic Au nanoparticles using aberration corrected in-situ electron microscopy. The activity of catalytic nanoparticles is thought to be highly sensitive to the particles' structure, meaning typical local atomic rearrangements are likely to significantly affect the overall performance of the catalyst. As-deposited Au nanoparticles are found to exhibit a variety of morphologies, with many being internally strained or highly stepped at the surface. Upon heating, surface atoms are observed to minimise the particles' surface energy by restructuring towards planar (111) facets, resulting in the removal of low co-ordinated sites thought to be crucial in catalysis by Au nanoparticles. These results suggest the process of surface energy minimisation made possible by heating may lead to a loss of active sites and consequently contribute to the deactivation of the catalyst.

Environmental TEM Observation of Deformations of Catalytic Gold Nanoparticles under Reaction Gas Condition

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.