Au Nanoparticle Composites Research Articles

Ratiometric electrochemical and impedimetric dual-mode aptasensor based on thionine-functionalized Ti3C2Tx MXene/Pt and Au nanoparticle composites for reliable detection of aflatoxin B1

Rapid and reliable detection of aflatoxin B1 (AFB1) is critical in public health, food safety and environmental control. Herein, a ratiometric electrochemical (EC) and electrochemical impedance spectroscopy (EIS) dual-mode aptasensing platform based on thionine-functionalized Ti3C2Tx MXene/Pt and Au nanoparticle composites (MXene@Thi/PtAuNPs) was constructed for accurate and reliable detection of AFB1. The MXene@Thi/PtAuNPs composites were prepared by a facile and mild approach. The electroactive molecule Thi embedded in MXene could not only inhibit the aggregation of MXene nanosheets, but also act as an internal reference probe to form a ratiometric sensing strategy. The decoration of Pt and Au nanoparticles can further effectively enhance the conductivity and catalytic activity of the composites. The MXene@Thi/PtAuNPs composites were then served as a support to sequentially assemble hairpin DNA (hDNA) and ferrocene-labelled AFB1 aptamer (Fc-Apt) to construct the dual-mode sensor. The developed dual-mode sensor with both ratiometric EC detection (based on IThi/IFc) and EIS detection (based on Ret) can mutually verify the detection results obtained by two modes, offering more accurate and reliable results, which enabled sensitive and reliable AFB1 detection in the concentration range of 10.0 pg mL−1-30.0 ng mL−1 (ratiometric EC mode) and 3.0 pg mL−1-30.0 ng mL−1 (EIS mode), respectively. The sensing platform also demonstrated favorable selectivity, reproducibility and stability, and satisfactory applicability in corn sample, showing great potential in the sensing of mycotoxins in agricultural products.

Environmental profiling of gold nanoparticles by flavonoids fractionalization from carrica papaya leaf extract for photocatalytic debasement of organic contaminants and it's cyto-toxic analysis

In present investigation, Carica papaya leaf extract has been employed as a bio-reductant agent in order to synthesize ecologically sustainable bio-coupled gold nanoparticles. The formation of gold nanoparticles was confirmed based on colour change of solution and its surface plasmon resonance peak measured using UV–Vis Spectrophotometer (UV–Vis). The Morphology and size of nanoparticles were determined using transmission electron microscope (SEM/TEM), and its crystalline structure by X-ray diffraction studies. Surface area was determined via BET isotherm analysis. The elemental composition of Au nanoparticles was developed using the technique of energy dispersive spectroscopy (EDS). Furthermore, FTIR analysis delineated the presence of functional groups present in the samples of the synthesized AuNPs. Thus, the efficiency of bio coupled Au nanoparticles in photo catalytically decomposing methylene blue was examined under the influence of visible light., the lethal MB colorant had been reduced to 95 % Within 90 min. And also 60% TOC removal was recorded after 5 min of degradation reaction, which increased to 99% after 90 min. Furthermore, cytotoxic experiments on Michigan Cancer Foundations-7 (MCF-7) cell lines showed that Au nanoparticles are effective anticancer agents with an IC50 of 87.2 g/mL on the top of the present work revealed the eco-safety and affordable production of Au nanoparticles from Carica papaya leaf extract, which displayed photocatalytic debasement of organic pollutants and cyto-toxicity effects was investigated.

Implementation of π-π interaction in AuNPs@GDY to boost the bioelectrocatalysis in enzymatic biofuel cells

The main challenges (sluggish electron transfer, low energy density) hinder the future application of enzymatic biofuel cells (EBFCs), which urgent to take effective measures to solve these issues. In this work, a composite of Au nanoparticles decorated graphdiyne (AuNPs@GDY) is fabricated and employed as the carrier of enzyme (G6PDH), and a mechanism based on π-π interaction of electron transfer is proposed to understand bioelectrocatalysis processes. The results show that the AuNPs@GDY composite exhibits the highest current density among the three materials (GDY, AuNPs, and AuNPs@GDY), which is 3.4 times higher than that of GDY and 2.5 times higher than that of AuNPs. Furthermore, the results reveal that the AuNPs could increase the loading of enzymes and provide more active site for reaction, while GDY provides highly π-conjugated structure and unique sp/sp2-hybridized linkages interface. This work provides new insights to explore a theoretical basis for the development of more efficient bioelectrocatalytic systems.

Synthesis of Porous Polydimethylsiloxane Gold Nanoparticles Composites by a Single Step Laser Ablation Process

Typically, polymeric composites containing nanoparticles are realized by incorporating pre-made nanoparticles into a polymer matrix by using blending solvent or by the reduction of metal salt dispersed in the polymeric matrix. Generally, the production of pre-made Au NPs occurs in liquids with two-step processes: producing the gold nanoparticles first and then adding them to the liquid polymer. A reproducible method to synthetize Au nanoparticles (NPs) into polydimethylsiloxane (PDMS) without any external reducing or stabilizing agent is a challenge. In this paper, a single-step method is proposed to synthetize nanoparticles (NPs) and at the same time to realize reproducible porous and bulk composites using laser ablation in liquid. With this single-step process, the gold nanoparticles are therefore produced directly in the liquid polymer. The optical properties of the suspensions of AuNPs in distilled water and in the curing agent have been analyzed by the UV-VIS spectroscopy, employed in the transmission mode, and compared with those of the pure curing agent. The electrical dc conductivity of the porous PDMS/Au NPs nanocomposites has been evaluated by the I–V characteristics. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis have monitored the composition and morphology of the so-obtained composites and the size of the fabricated Au nanoparticles. Atomic force microscopy (AFM) has been used to determine the roughness of the bulk PDMS and its Au NP composites.

Selective and Sensitive Determination of Folic Acid Based on Molecularly Imprinted Poly (o-aminophenol) and Reduced Graphene Oxide Decorated with Au Nanoparticles

Background: Folic acid (pteroylglutamic acid, FA), known as a water soluble vitamin of B complex family, plays an important role in the human body. However, excess intake of FA would mask the vitamin B12 deficiency symptoms which may lead to other health risks. Therefore, it is very important to develop a method for the sensitive and selective determination of FA in natural sources, fortified foods and multivitamin preparations. Methods: An electrochemical sensor was fabricated for the analysis of FA, which was based on electropolymerized molecularly imprinted poly (o-aminophenol) film and reduced graphene oxide decorated with Au nanoparticles composites (rGO-AuNPs). The transmission electron microscope, cyclic voltammetry, electrochemical impedance spectroscopy and differential pulse voltammetry were utilized for the characterization of the imprinted polymer film. Results: Under the optimized experimental conditions, the proposed sensor exhibited two distinct linear responses ranging from 0.02 to 0.8 μmol L-1 and 0.8 to 10 μmol L-1 towards the concentrations of FA, and the detection limit was found to be 2.8 nmol L-1 (S/N=3). The molecularly imprinted film proposed was also found to exhibit comparatively high selectivity toward folic acid against structurally similar analogues, and the preparation of the sensor was simple and reproducible. Conclusions: In this work, a molecularly imprinted film fabricated on an rGO-AuNPs modified electrode was developed for the sensitive and selective determination of FA. Furthermore, the method was applied to the detection of FA in infant formula milk, multivitamin tablets and blood serum sample with satisfactory results.

Nano‐Sized Au Particle‐Modified Carbon Nanotubes as an Effective and Stable Cathode for Li−CO2 Batteries

AbstractLithium‐carbon dioxide (Li−CO2) batteries show a great potential in the fields of CO2 fixation and energy storage, and moreover the research of Li−CO2 batteries is of great significance to the practical application of Lithium‐air (Li‐air) batteries. However, the sluggish kinetics and high charging potential causing by the wide band gap insulator Li2CO3 make it extremely important to research cathode catalysts that can promote the decomposition of Li2CO3 and reduce the charge potential. Here, we prepared a composite of Au nanoparticles uniformly distribute on carbon nanotubes (CNTs) network (AuNPs/CNTs) as an efficient cathode catalyst. Benefitted by the small sized Li2CO3 which is easier to decompose during charge process, the AuNPs/CNTs‐based batteries exhibit a high specific capacity of 6399 mAh g−1, a low overpotential of 1.53 V and a stable cycling performance of 46 cycles, demonstrating the conspicuous catalytic performance of AuNPs/CNTs.

Enhancing the photocatalytic activity of TiO2 and TiO2–SiO2 by coupling with graphene–gold nanocomposites

In the present paper, a novel composite Graphene–Gold (Gr–Au)/TiO2–SiO2 photocatalyst was synthesized and tested for the removal of methylene blue and rhodamine B in water solutions. First, Gr–Au nanoparticle composite was synthesized by simultaneous reduction and deposition of Au nanoparticles on Gr surface. The photodegradation of methylene blue and rhodamine B in aqueous solutions was studied using various photocatalysts, including neat TiO2–SiO2, Gr/TiO2–SiO2 and Gr–Au/TiO2–SiO2 composites. The Gr weight ratio in this research is 2% in the Gr/TiO2–SiO2 composites. Detailed characterization (field emission scanning electron microscope, Raman, Fourier transform infrared spectra and UV–vis absorbance spectroscopy) of such material was conducted. As a result, the uniform deposition of nanometer-sized Au NPs on the graphene sheets was observed. The Gr–Au/TiO2–SiO2 exhibited excellent photocatalytic efficiency because of the reduction of electron–hole recombination. The Gr2%–Au0.1%/TiO2–SiO2 composite had the highest photoactivity.

A highly selective electrochemical sensor based on surface molecularly imprinted copolymer for the detection of 5-hydroxytryptamine

In this work, a novel composite of Au nanoparticles (Au NPs), ionic liquid (i.e. 1-aminopropyl-3-methylimidazolium bromine, [APMIM]Br) and multi-walled carbon nanotubes (MWCNTs@IL-Au) is prepared through ion-exchange and Au-N coordination between MWCNTs, IL, and Au NPs under mild conditions. The composite is used as support, itaconic acid (IA) and acrylamide (Aam) as functional monomers, 5-hydroxytryptamine (5-HT) as template molecule, ethylene glycol dimethylacrylate (EGDMA) as cross-linking agent and azobisisobutyronitrile (AIBN) as initiator are mixed to synthesize surface imprinted copolymer (DSMIP). The obtained DSMIP-MWCNTs@IL-Au has good conductivity and strong adsorption capacity for 5-HT due to hydrogen bonding and electrostatic interaction. When it is immobilized on a glassy carbon electrode for the electrochemical determination of 5-HT, the resulting sensor presents a wide linear response range (i.e. 0.20–10 μmol L−1 and 10–400 μmol L−1) and low limit of detection (i.e. 0.080 μmol L−1). Furthermore, it shows high selectivity, stability and reproducibility. To evaluate its practicability, the sensor is applied to the determination of 5-HT in human serum and human urine samples, and comparable results are achieved.

Dual origins of photocatalysis: Light-induced band-gap excitation of zirconium oxide and ambient heat activation of gold to enable 13CO2 photoreduction/conversion

Photoconversion of CO2 into fuels completes the carbon neutral cycle in a sustainable society. To exclude the contribution of adventitious carbon, monitoring the time course of 13CO2 conversion into 13C-fuel is essential, but has been rarely reported. In the present work, a composite of Au nanoparticles with ZrO2 was found to be effective in converting 13CO2 into 13CO at a rate of 0.17 μmol h−1 gcat−1 in the presence of H2 and UV–vis light. The detected 12CO as a minor byproduct (11.9 %) was identified as due to adsorbed 12CO2 from the air. The 12C ratio in the total amount of CO2 was evaluated based on a 13CO2 photoexchange reaction (8.7 %). The discrepancy between these values suggested a slower exchange reaction step between the chemisorption site for CO2 reduction and the physisorption site for CO2 compared to the reduction step to CO. Furthermore, based on in-profile kinetic studies using sharp-cut filters and control reactions in the dark, the contribution ratio for CO2 conversion was determined to be via charge separation at the band-gap of ZrO2 (λ < 320 nm): 69 % and via ambient heat (12kT): 31 %. Localized surface plasmon resonance (LSPR) absorption of Au and infrared absorption in the range of λ > 320 nm did not promote catalysis. The LSPR absorption was further investigated by Au L3-edge extended X-ray absorption fine structure analysis. Ambient heat on the Au nanoparticles should have promoted H2 activation enough, supplying protons to the CO2 reduction sites over ZrO2; however, a temperature increase of 26 K on the Au surface was marginal for further H2 activation. CO2 photoconversion with added moisture was also attempted; the CO formation rate using ZrO2 under these conditions was 0.15 μmol h−1 gcat−1. However, 47 % was characterized as 12CO originating from chemisorbed 12CO2, and H2 was also formed at a comparable rate of 0.14 μmol h−1 gcat−1 from a competing reaction. The addition of Au to ZrO2 was found to suppress CO formation and promote H2 formation, and Mg2+ addition to Au–ZrO2 effectively suppressed H2 formation directing to the CO formation.

Gold Electrode Fused with AuNPs/GQDs Showing Enhanced Electrochemical Performance for Detection of Phenolic Compounds

Gold electrode (GE) is modified with composite of Au nanoparticles (AuNPs) and graphene quantum dots (GQDs), and its electrochemical performance is evaluated. The modified electrode (GE/AuNPs/GQDs) exhibits higher electrochemical activity and better stability than bare GE and AuNPs or GQDs modified GEs. The higher electrochemical activity of GE/AuNPs/GQDs is attributed to the increase of the active surface area and the decrease of the interface transfer resistance that accelerates reactant absorption and electron transfer of the electrodes. In addition, π-π interaction between GQDs in the GE/AuNPs/GQDs and aromatic rings of phenolic compounds contributes to the enhanced electrochemical activity in detection of phenolic compounds. Given the high electrochemical activity and long cycling stability, the method for GE modification can be applicable to the detection of phenolic compounds.

Au nanoparticles controlled by lattice Zn2+ of supports

Supported Au nanoparticles (NPs) have attracted much attention in catalytic field because of their high activity and selectivity. However, its activity was affected by its dispersion. In this work, a controlled impregnation method was used to prepare Au/Zn-hydrotalcites (Au/Zn-HTs). The role of lattice Zn2+ in controlling Au NPs was studied. The size, structure, and composition of Au NPs were characterized using techniques of nitrogen physisorption, X-ray diffraction, scanning transmission electron microscopy, temperature-programmed reduction, and X-ray photoelectron spectroscopy. The mean size of Au/Zn-HTs by this work was 1.8 nm, which was smaller than the mean size of catalysts by traditional method. The mechanism of forming Au NPs was investigated. There was electron transfer between Au and Zn2+, displaying the interaction between them. It was found that dispersion of Zn2+ and the interaction between Au and Zn were two key factors affecting the dispersion of Au NPs. The dispersion of Zn2+ could be controlled by adjusting its content in HTs. The yield of acetophenone was 92% by Au/Zn-HTs, while it was below 65% for catalysts prepared by traditional method.

Enhancement of corrosion resistance and bioactivity of titanium by Au nanoparticle-loaded TiO2 nanotube layer

Abstract To further improve the modified benefit of TiO 2 nanotube (TN) arrays as an implant surface layer, Au nanoparticles (AuNPs) were uniformly loaded into TN arrays by using a simple electrochemical deposition method. Morphology, phase composition, surface roughness, and water contact angle of as-prepared AuNP–TN arrays were examined through various characterizations. AuNP–TN arrays exhibited much rougher surface and higher surface energy than pure Ti and TN arrays without loading of AuNPs. The corrosion behavior in simulated body fluids was evaluated by a potentiodynamic polarization test, and the corrosion resistance of the AuNP–TN arrays was significantly enhanced. In vitro bioactivity assessments showed that the AuNP–TN arrays possessed higher apatite-forming ability than pure Ti and TN arrays. In vitro cell culture tests also confirmed that the AuNP–TN array surface could promote osteoblast cell attachment and proliferation. The highly active surface of AuNP–TN arrays was believed to provide a solid and practical foundation of effective substrate for implant designs.

Layered Metal Nanoparticle Structures on Electrodes for Sensing, Switchable Controlled Uptake/Release, and Photo-electrochemical Applications.

Layered metal nanoparticle (NP) assemblies provide highly porous and conductive composites of unique electrical and optical (plasmonic) properties. Two methods to construct layered metal NP matrices are described, and these include the layer-by-layer deposition of NPs, or the electropolymerization of monolayer-functionalized NPs, specifically thioaniline-modified metal NPs. The layered NP composites are used as sensing matrices through the use of electrochemistry or surface plasmon resonance (SPR) as transduction signals. The crosslinking of the metal NP composites with molecular receptors, or the imprinting of molecular recognition sites into the electropolymerized NP matrices lead to selective and chiroselective sensing interfaces. Furthermore, the electrosynthesis of redox-active, imprinted, bis-aniline bridged Au NP composites yields electrochemically triggered "sponges" for the switchable uptake and release of electron-acceptor substrates, and results in conductive surfaces of electrochemically controlled wettability. Also, photosensitizer-relay-crosslinked Au NP composites, or electrochemically polymerized layered semiconductor quantum dot/metal NP matrices on electrodes, are demonstrated as functional nanostructures for photoelectrochemical applications.

A biomimetic enzyme modified electrode for H2O2 highly sensitive detection.

An efficient catalyst based on artificial bionic peroxidase was synthesized for electrocatalysis. A poly(ethyleneimine)/Au nanoparticle composite (PEI-AuNP) was prepared and it was then linked to hemin via a coupling reaction between carboxyl groups in hemin and amino groups in PEI without the activation of a carboxyl group by carbodiimide. Fourier transform infrared (FTIR) spectroscopy verified the formation of amido bonds within the structure. The presence of AuNPs contributed greatly in establishing the amido bonds within the composite. Transmission electron microscopy (TEM) and UV-visible spectroscopy were also used to characterize the PEI-AuNP-hemin catalyst. PEI-AuNP-hemin exhibited intrinsic peroxidase-like catalytic activities. The PEI-AuNP-hemin deposited on a glass carbon electrode had strong sensing for H2O2 with a well-defined linear relationship between the amperometric response and H2O2 concentration in the range from 1 μM to 0.25 mM. The detection limit was 0.247 nM with a high sensitivity of 0.347 mA mM(-1) cm(-2). The peroxidase-like catalytic activity of PEI-AuNP-hemin is discussed in relation to its microstructure. The study suggests that PEI-AuNP-hemin may have promising application prospects in biocatalysis and bioelectronics.

Improved photocatalytic activity of self-assemble TiO 2 nanobelts with Au nanoparticles

Self-assemble TiO2 nanobelts composited with Au nanoparticles were prepared by hydrothermal method and followed by the deposition of Au nanoparticle on the surface of spheres. It is found that the Au/s-TiO2 sample exhibits a much better photocatalytic activity under UV light irradiation, compared with s-TiO2 and TiO2 nanoparticles. The band gap is enlarged because of the quantum confinement effect, accompanying stronger redox ability; the specific surface area is also increased due to unique self-assemble one-dimensional nanobelts; the composition of Au nanoparticles would promote the separation of charge carriers. All these factors contribute to the enhanced photocatalytic activity of Au/s-TiO2, indicating the potential application of the self-assemble low-dimensional nanostructure as new improved functional nano-materials.

MnO2–Au Composite Electrodes for Supercapacitors

Abstract The MnO2 nanorod–Au nanoparticle composites that exhibit superior supercapacitance and long-term durability have been fabricated using a two-step procedure. The role of Au nanoparticles is not only to improve the electrical conductivity but also to enhance the structural stability. The composites have a specific capacitance of 406.8 F g−1 at a scan rate of 50 mV s−1, which is almost five times that of the pure MnO2 nanorods. The composites have 91.3% capacitance retention over 2000 charge–discharge cycles at 5 A g−1, which is much better than the capacitance retention of pure MnO2 nanorods (74.6%).

Electrochemical detection of 4-nitrophenol based on a glassy carbon electrode modified with a reduced graphene oxide/Au nanoparticle composite

A new electrochemical sensor for 4-nitrophenol (4-NP) detection based on the reduced graphene oxide (RGO) and Au nanoparticle composite was developed. The RGO film was first electrodeposited onto a glassy carbon electrode (GCE). Then Au nanoparticles (AuNPs) were electrochemically deposited onto the RGO film. The morphology and electrochemical properties of the AuNP/RGO composite were investigated. The synergic effect of AuNPs and RGO nanosheets as co-modifiers greatly facilitates electron-transfer processes between the electrolyte and the GCE, and thus leads to a remarkably improved sensitivity for 4-NP detection. Two detection modes, differential pulse voltammetry (DPV) and square wave voltammetry (SWV), were applied. A wide linear range of values, 0.05–2.0 μM and 4.0–100 μM for DPV and 0.05–2.0 μM for SWV, were obtained. The limit of detection (LOD) of 4-NP was 0.01 μM and 0.02 μM for DPV and SWV, respectively. This sensor was successfully used in the detection of real water samples from Xiangjiang River.

Size-Controlled Electron Transfer and Photocatalytic Activity of ZnO–Au Nanoparticle Composites

This Letter describes size-controlled photocatalytic activity of ZnO nanoparticles coated with glutathione-protected gold nanoparticles with diameters of 1.1, 1.6, and 2.8 nm. The photocatalytic activity of the ZnO–Au composites was found to increase with increasing gold size for both oxidative and reductive catalytic reactions. Photoluminescence decay dynamics of the composites showed that the electron-transfer rate from the photoexcited ZnO to gold nanoparticle also increased as the gold size increased. These results demonstrate that the photogenerated electron transfer and the resulting catalytic activity of the composites can be controlled by the size of the mediating gold capacitors.

Electrochemically Triggered Au Nanoparticles “Sponges” for the Controlled Uptake and Release of a Photoisomerizable Dithienylethene Guest Substrate

1,2-Di(2-methyl-5-(N-methylpyridinium)-thien-3-yl)-cyclopentene undergoes a reversible photoisomerization between open and closed states. The closed isomer state exhibits electron acceptor properties, whereas its irradiation using visible light (λ > 530 nm) yields the open state that lacks electron acceptor features. The electropolymerization of thioaniline-functionalized Au nanoparticles (NPs) in the presence of the closed photoisomer state yields a molecularly imprinted Au NPs matrix, cross-linked by redox-active bis-aniline π-donor bridges. The closed isomer is stabilized in the imprinted sites of the bis-aniline-bridged Au NPs composite by donor-acceptor interactions. The electrochemical oxidation of the bis-aniline bridging units to the quinoid acceptor state leads to imprinted sites that lack affinity interactions for the binding of the closed state to the matrix, leading to the release of the closed photoisomer to the electrolyte solution. By the cyclic reduction and oxidation of the bridging units to the bis-aniline and quinoid states, the reversible electrochemically controlled uptake and release of the closed photoisomer is demonstrated. The quantitative uptake and release of the closed isomer to and from the imprinted Au NPs composites is followed by application of CdSe/ZnS quantum dots as auxiliary probes. Similarly, by the reversible photochemical isomerization of the closed substrate to the open substrate (λ > 530 nm) and the reversible photoizomerization of the open substrate to the closed state (λ = 302 nm), the cyclic photonic uptake and release of the closed substrate to and from the imprinted Au NPs matrix are demonstrated. Finally, we demonstrate that the electrochemically stimulated uptake and release of the closed substrate to and from the imprinted Au NPs composite controls the wettability of the resulting surface.

Preparation and optical limiting properties of carbon nanotubes coated with Au nanoparticle composites embedded in silica gel-glass

Au nanoparticle (NP) coated carbon nanotubes (CNTs) (CNTs@AuNPs) embedded in silica gel-glass (CNTs@AuNPs/silica gel-glass) were prepared by the sol–gel technique. Subsequent analysis confirmed the successful introduction of the CNTs@AuNPs to the silica gel-glass. Coating with AuNPs dramatically improved the mechanical properties of the silica gel-glass matrix, despite the higher Brunauer–Emmett–Teller (BET) specific surface area and pore volume of the CNTs@AuNPs/silica gel-glass compared with CNT/silica gel-glass. The optical limiting (OL) properties of the CNTs@AuNPs measured at a laser wavelength of 532 nm were slightly weaker after introduction into the solid-state matrix. This reduction is probably attributed to the synergistic nonlinear optical effects of reverse saturable absorption arising from the CNTs and saturable absorption from the AuNPs embedded in the silica gel-glass.