Well-dispersed Gold Nanoparticles Research Articles

Photocatalytically induced Au/mpg-C3N4 nanocomposites for robust electrochemical detection of Cr(VI) in tannery wastewater

Chromium readily undergoes redox speciation, and Cr(VI) oxidation state is ubiquitous and mobile in the environment. Under physiological conditions, Cr(VI) reduction yields species as Cr(V) or Cr(VI), which shows reactivity towards DNA damaging. Therefore, accurate detection of Cr species in the environmental compartment is of utmost importance. In compliance with green chemistry, Au/mpg-C3N4 nanocomposites were successfully fabricated by ultra-violet photo-reduction without a reducing agent. The Au/mpg-C3N4 nanocomposites were characterized by scanning electron microscope (SEM), X-ray diffractometry (XRD), X-ray photoelectron spectrometry (XPS), and infrared spectrophotometry. Well-dispersed gold nanoparticles with an average diameter of 50 nm decorated on mpg-C3N4. We developed a method to determine Cr(VI) with excellent sensitivity (0.002196 μA/ppb) and detection limit (14.7 ppb) using Au/mpg-C3N4 modified glassy carbon working electrode by linear sweep voltammetry (LSV). The same electrode can use in real-time Cr(VI) monitoring using amperometry. The new sensor is stable and free from interferences from other species in natural water, and it can also be used in real-time Cr(VI) monitoring over wide concentration ranges.

Temperature-responsive mesoporous silica nanoreactor with polymer gatings immobilized surface via a ‘grafting-to’ approach as peroxidase-like catalyst

Abstract An efficient gold decorated mesoporous silica/polymer hybrid nanoreactor was prepared for catalytic applications. The Huisgen cyclo-addition method was used to immobilize poly(2-(dimethylamino)ethyl methacrylate (PDMAEMA) gatings on the surface of the mesoporous silica using a ‘grafting-to’ approach. The catalyst particles exhibited well-ordered mesoporous structural integrity with well-dispersed gold nanoparticles showing resonance plasma absorption. The catalyst exhibited efficient peroxidase like activity for the oxidation of 3,3,5,5-tetramethylbenzidine in the presence of H2O2, which was found to be in consistent with the standard Michaelis-Menten kinetics. The change in the catalytic activity with temperature was evaluated using 4-nitrophenol reduction as the model reaction. The catalyst showed nonlinear variation of the rate constants with temperature. A sharp decrease in the rate constant was observed above 35 °C due to the thermodynamic volume phase transition of the grafted PDMAEMA chains. In contrast, a typical Arrhenius-type dependence of the rate constant on temperature was observed above and below the transition temperature of PDMAEMA.

Mercapto-Functionalized Porous Organosilica Monoliths Loaded with Gold Nanoparticles for Catalytic Application.

Porous organosilica monoliths have attracted much attention from both the academic and industrial fields due to their porous structure; excellent mechanical property and easily functionalized surface. A new mercapto-functionalized silicone monolith from a precursor mixture containing methyltrimethoxysilane; 3-mercaptopropyltrimethoxysilane; and 3-mercaptopropyl(dimethoxy)methylsilane prepared via a two-step acid/base hydrolysis–polycondensation process was reported. Silane precursor ratios and surfactant type were varied to control the networks of porous monolithic gels. Gold nanoparticles were loaded onto the surface of the porous organosilica monolith (POM). Versatile characterization techniques were utilized to investigate the properties of the synthesized materials with and without gold nanoparticles. Scanning electron microscopy was used to investigate the morphology of the as-synthesized porous monolith materials. Fourier transform infrared spectroscopy was applied to confirm the surface chemistry. 29Si nuclear magnetic resonance was used to investigate the hydrolysis and polycondensation of organosilane precursors. Transmission electron microscopy was carried out to prove the existence of well-dispersed gold nanoparticles on the porous materials. Ultraviolet–visible spectroscopy was utilized to evaluate the high catalytic performance of the as-synthesized Au/POM particles

Ultrafast synthesis of gold nanoparticles on cellulose nanocrystals via microwave irradiation and their dyes-degradation catalytic activity

This study represents a well-dispersed gold nanoparticles (AuNPs) synthesis process via cellulose nanocrystals (CNC) which acts as both reducing and supporting agent. The synthesis process was ultrafast and completed in a few seconds using microwave irradiation. The entire synthesis process was cost-effective, sustainable and eco-friendly. The synthesized (AuNPs/CNC) nanocomposite was investigated by transmission electron microscopy, selected area electron diffraction, Fourier transform infrared spectroscopy, energy dispersive X-ray analysis, X-ray diffraction, and UV–vis spectroscopy. The obtained AuNPs were well accumulated on the CNC surface and had a uniform spherical shape with an average diameter of 8 ± 5.3 nm. The diameter of AuNPs could be altered by tuning the concentration of CNC suspension. The synthesized AuNPs/CNC nanocomposite film exhibited excellent degradation properties against various organic dyes, namely, Allura red, Congo red, Rhodamine B and Amaranth. The ultrafast degradation reactions followed pseudo first order kinetics. In the catalytic degradation reaction, AuNPs/CNC was transmitting electrons from a donor (NaBH4) to an acceptor (a dye).

In-situ graft-crosslinked gold nanoparticles with high-density surface defects and coated with a polytaurine membrane for the voltammetric determination of dopamine

Well-dispersed and graft-crosslinked gold nanoparticles (AuNPs) were synthesized by the reduction of tetrachloroaurate with hydrazine at room temperature. The AuNPs possess a high density of surface defects which is due to grafting of n-octanoic acid to polyvinylpyrrolidone. The physical and chemical properties of the resulting AuNPs were characterized by UV-vis, XRD, TEM/HRTEM, SAED, and XPS, respectively. The modified AuNPs were placed on a glassy carbon electrode (GCE) in an electropolymerized taurine layer to obtain a sensitive, selective, stable and rapid electrochemical dopamine sensor. The peak current, typically measured at 0.17V (vs. SCE), increases linearly in the 1.0 to 120μM dopamine concentration range, and the limit of detection (at S/N= 3) is 0.16μM with a sensitivity of 2.94μA·μM-1·cm-2. The sensor was successfully applied to the determination of dopamine in injections and spiked serum samples. The recoveries from spiked serum samples range from 97.5 to 102.4%, with RSDs ranging between 2.8 and 3.4%. Graphical abstract Schematic representation of a glassy carbon electrode modified with in-situ graft-crosslinkedgold nanoparticles combined with an electropolymerized polytaurine membrane. The sensor exhibits excellent features towards dopamine determination.

Eco-synthesis of gold nanoparticles by Sericin derived from Bombyx mori silk and catalytic study on degradation of methylene blue

In recent years, the eco-friendly synthesis of noble metal nanoparticles using bio-resources has given rise to a new trend in nanoscience and nanotechnology. In the present work, well-dispersed gold nanoparticles (AuNPs) are synthesized by redox of chloroauric acid (HAuCl4.H2O) using Silk Sericin (SS) obtained from Bombyx mori cocoons. The selection of SS, a textile industry waste, as a bio template is mainly due to its dual action as a metal ion reduction and stabilizer of the formed nanoparticles. The formed AuNPs are characterized by a transverse peak in the wavelength range λ = 530–540 nm in the UV–visible spectra and characteristic Bragg’s reflections observed in the XRD profile. The transmission electron microscopy (TEM) indicates the evolution of spherical AuNPs with the radii of individual particles in the range of 5–15 nm. The X-ray photoelectron spectroscopy (XPS) study showed two distinct peaks separated by 3.65 eV are observed due to the splitting of the Au4f level. Further, the potential catalytic action of the AuNPs is evaluated on the reduction of Methylene blue (MB). The study confirms the degradation of MB as a function of AuNPs concentration. Almost all the MB dye degrades in the highest AuNPs concentration.

Two-dimensional titanate-based zwitterionic hydrophilic sorbent for the selective adsorption of glycoproteins

The selective adsorption towards glycoproteins from complex biosamples is of vital importance in life science studies. A new zwitterionic hydrophilic material, i.e., a functionalized titanate nanosheet, is prepared by assembling well-dispersed gold nanoparticles (AuNPs) on the surface of ultrathin titanate nanosheets via an ion-exchange approach, followed through immobilizing l-cysteine (L-Cys) by Au-S bonding. This 2D-titanate-based zwitterionic hydrophilic material is shortly termed as L-Cys/Au/TiNSs and it exhibits transverse several hundred nanometers with an ultrathin nanosheet structure. The zwitterionic hydrophilic titanate nanosheets have strong adsorption affinity to glycoproteins, offering a large binding capacity towards immunoglobulin G (1098.9 mg g−1), which could be readily stripped into an ammonium hydroxide (NH4OH) solution (0.5%, m/v) with a recovery of 82.4%. The practical applications of L-Cys/Au/TiNSs are further proved by successful specific adsorption of IgG from human serum.

Visual Detection of Melamine in Urine Based on an AuNPs-Curcumin System

Abstract A colorimetric method involving a novel gold nanoparticle-curcumin system is described for determination of melamine in urine. The natural phenol curcumin can reduce chloroauric acid to form well-dispersed gold nanoparticles, while at high concentration of melamine, reduction is suppressed and blue aggregates are quickly formed, which is confirmed by UV-vis spectroscopy and TEM images. The ratio of absorbances at 673 and 546 nm increases linearly in the 0.5 to 4 ppm melamine concentration range, and the detection limit is 0.16 ppm. The assay has been applied to analyze urine samples and showed recoveries with RSDs of <5%. The gold nanoparticle-curcumin based analytical system is simple for one-pot synthesis, convenient for visual detection and rapid requiring only 30 min. Therefore, it is a promising assay approach for melamine adulteration and well suited for homecare testing.

Biocompatible, small-sized and well-dispersed gold nanoparticles regulated by silk fibroin fiber from Bombyx mori cocoons

Biocompatible, small-sized but well-dispersed gold nanoparticles (Au NPs) remain a major challenge for their synthesis. Here a convenient solution impregnation technique is developed to prepare such Au NPs under the regulation of degummed silk fibroin fibers (SFFs) extracted from Bombyx mori cocoons. SFFs play multiple roles in the formation of Au NPs such as reactive substrate to capture AuCl4- ions by the chelation of -C = O, reducing agent for Au(0) by the reduction of -OH, and modifiers to render biocompatible Au NPs by some functional groups and biomolecules. The as-prepared Au NPs with a size of 7–10 nm are embedded in the solid SFF substrate, and can disperse well in the liquid system by the disintegration of SFFs into silk fibroin (SF) in a certain CaCl2 solution. The biocompatible Au NPs exhibit uniform small size and distribute stably in both solid and solution states, which have distinctive properties and functional advantages, and bring great convenience to their storage and transportation.

Polymer-Templated Gold Nanoparticles on Optical Fibers for Enhanced-Sensitivity Localized Surface Plasmon Resonance Biosensors.

Dense arrays of well-dispersed gold nanoparticles (AuNPs) on optical fibers are shown to bridge the gap in sensitivity and sensing performance between localized surface plasmon resonance (LSPR) and classical SPR sensing. A simple self-assembly method relying on a poly(styrene- b-4-vinylpyridine) (PS- b-P4VP) block copolymer brush layer was used to immobilize AuNPs of different diameters from 10 to 92 nm on optical fibers. In comparison with standard AuNP deposition methods using (3-aminopropyl)trimethoxysilane (APTMS) and polyelectrolytes, the sensitivity with the PS- b-P4VP templating method was found to be 3-fold better, a consequence of the smaller gap between particles and the presence of fewer AuNP aggregates. Hence, the sensitivity of the LSPR sensor for IgG was comparable to a classical SPR, also on optical fibers, and about 68% of that for a prism-based wavelength-interrogation SPR instrument. The reproducibility and the detection limit of the LSPR sensor were about the same as the SPR sensor. The enhanced performance of the LSPR sensors using the PS- b-P4VP block copolymer fabrication method paves the way for use of these LSPR biosensors in a smaller and more cost-effective platform.

Hierarchically assembled two-dimensional gold boron nitride-tungsten disulphide nanohybrid interface system for electrobiocatalytic applications

Abstract In this study, we report for the first time, the fabrication of hybrid dual 2D-nanohybrid structure as an interface system for electrochemical biosensing, bioelectronics, and electrobiocatalysis devices through self-assembly combination of gold nanoparticles (AuNPs) with hybrid 2D materials consisting of boron nitride (BN) and tungsten disulphide (WS2). Horseradish peroxidase (HRP) was immobilized on the hybrid dual 2D-nanoparticle system to form a biointerface system. Structural characterization showed high crystallinity in the fabricated structure, while morphological characterization confirmed the high surface area of the hybrid material and the presence of well-dispersed gold nanoparticles (AuNPs). Electrochemical characterization also confirmed that the fabricated HRP/BN/WS2/AuNPs/GC bioelectrode exhibited excellent electron transfer properties at the interface. The electrobiocatalytic activity of the nanohybrid interface structure was studied using hydrogen peroxide (H2O2) as a model analyte. The fabricated bioelectrode exhibited a wide linear range from 0.15 mM to 15.01 mM towards hydrogen peroxide detection with a limit of detection of 3.0 mM (S/N = 3) and a sensitivity of 19.16 μA/mM/cm2. A density functional theory (DFT) calculation was also used to validate the charge transport mobility and conductivity of BN/Au/WS2(001) nanohybrid structure as biosensing interface material. The DFT calculations combined with the experimental studies showed that the BN/Au/WS2(001) nanocomposite enhances the performance of the nanocomposite as sensor due to the introduction new electronic states emanating from the N 2p orbital. This work thus set the stage for the use BN/WS2/AuNPs nanohybrid system as interface material for bioelectronics and biosensing devices fabrications and applications.

Highly sensitive detection of bisphenol A in real water samples based on in-situ assembled graphene nanoplatelets and gold nanoparticles composite

The in-situ assembly of well-dispersed gold nanoparticles (AuNPs) and graphene nanoplatelets (GNPs) composite was carried out. The GNPs-AuNPs composite was characterized by Raman spectroscopy, transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). GNPs-AuNPs modified glassy carbon electrode (GNPs-AuNPs/GCE) was fabricated, and its electrochemical behaviors were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV). The highly sensitive and selective determination of bisphenol A (BPA) at GNPs-AuNPs/GCE in sulfuric acid solution was observed by DPV. Plots of peak currents versus BPA concentrations were fitted successfully to obtain a linear relationship and a nonlinear relationship in the BPA concentration range of 5 × 10−3–100 μM and 0.05–500 nM with good coefficient of determination (R2), respectively. The limit of detection (LOD) was calculated to be 0.027 nM. The recoveries of quantitative analysis of BPA in mountain spring water and tap water at GNPs-AuNPs/GCE were in the range of 96.9%–103.3% and 97.9%–104.2%, with relative standard deviation (RSD) in the range of 0.12–1.10% and 0.48–1.78%, respectively. The GNPs-AuNPs/GCE possessed good anti-interference ability, stability, repeatability, and reproducibility. It could be used as a simple, fast and sensitive electrochemical sensor electrode for determining trace amount of BPA in water samples.

Tailorable Au Nanoparticles Embedded in Epitaxial TiO2 Thin Films for Tunable Optical Properties.

The unique property of plasmonic materials to localize light into deep sub-wavelength regime has greatly driven various applications in the field of photovoltaics, sensors, and photocatalysis. Here, we demonstrate the one-step growth of an oxide-metal hybrid thin film incorporating well-dispersed gold (Au) nanoparticles (NPs) with tailorable particle shape and diameters (ranging from 2 to 20 nm) embedded in highly epitaxial TiO2 matrix, deposited using pulsed laser deposition. Incorporation of Au NPs reduces the band gap of TiO2 and enhances light absorption in the visible regime owing to the excitation of localized surface plasmons. Optical properties, including the plasmonic response and permittivity, and photocatalytic activities of the Au-TiO2 hybrid materials are effectively tuned as a function of the Au NP sizes. Such optical property tuning is well captured using full-field simulations and the effective medium theory for better understanding of the physical phenomena. The tailorable shape and size of Au NPs embedded in TiO2 matrix present a novel oxide-metal hybrid material platform for optical property tuning and highly efficient plasmonic properties for future oxide-based photocatalytic sensors and devices.

Gold nanoparticles, capped by carboxy-calix[4]resorcinarenes: effect of structure and concentration of macrocycles on the nanoparticles size and aggregation

Small (dcore ≈ 2–5 nm) well-dispersed gold nanoparticles (AuNPs) stabilized by amphiphilic octacarboxy-calix[4]resorcinarenes with different substituents on the lower rim—methyl (С1–CR), pentyl (С5–CR) and undecyl (С11–CR)—in an aqueous solution were obtained. The nanoparticles were studied by spectrophotometry, transmission electron microscopy, FTIR-spectroscopy, dynamic light scattering, small angle X-ray scattering and X-ray powder diffraction. The influence of HAuCl4/macrocycle ratio during the synthesis on the nanoparticles size and aggregation only for weakly associated С1–CR and С5–CR was achieved. The self-association effect of С11–CR on the nanoparticles stabilization is found. The existence of gold in the form of crystallites and their average sizes were defined. The average nanoparticle sizes were determined and the structure of macrocyclic shells on the surface of nanoparticles in an aqueous solution was proposed. The formation of cooperative calix[4]resorcinarene associates on the AuNPs surface due to the multiple supramolecular interactions leads to the creation of functional gold nanoparticles.

Synthesis of AuNPs@RGO nanosheets for sustainable catalysis toward nitrophenols reduction

A facile, green and one-pot synthesis strategy for the convenient preparation of well-dispersed gold nanoparticles (AuNPs) decorated reduced graphene oxide (RGO) without using any other toxic chemicals and reductants is reported herein. The synthesized AuNPs@RGO hybrid nanomaterials were characterized by UV–visible absorption spectroscopy, FT-IR, XRD, Raman, SEM, TEM and EDX analysis. The AuNPs@RGO acts as an efficient catalyst for the reduction of organic nitroaromatics (2- & 4-nitro phenols) in the presence of NaBH4. This newly synthesized hybrid AuNPs@RGO has superior catalytic activity over any other Au-nanomaterials ever reported. The rate of nitro aromatics reduction is found to be dependent on concentrations of substrate, reductant and catalyst. The mechanisms for the synthesis and catalytic reduction have been studied and discussed.

Toward an Effective Control of the H2 to CO Ratio of Syngas through CO2 Electroreduction over Immobilized Gold Nanoparticles on Layered Titanate Nanosheets

In recent years, the electroreduction of CO2 to valuable products has emerged as a rational answer to rising CO2 emissions and a strategic approach to incorporate renewable electricity from intermittent sources (e.g., wind and solar) into the global energy supply. The reduction of CO2 to CO has been highlighted in the widely explored industrial conversion of syngas (CO and H2) to fuels. Herein, we report a promising electrocatalyst incorporating well-dispersed gold nanoparticles (Au NPs) on ultrathin titanate nanosheets (TiNS). By tuning the contents of Au (in the ranges of 0 to 93 wt % Au) in the hybrid Au/TiNS architecture, CO product selectivity was effectively controlled (in the range of CO Faradaic efficiency from 3 to over 80%) with the sole additional formation of H2, which is of pronounced industrial interest. Most importantly, a control of both component amounts was suggested to result in a variation of corresponding electronic properties based on the interaction between Au NP and TiNS substrate, dictating the stabilization of formed reaction intermediates and resulting product selectivity. In addition, our Au/TiNS achieved optimally high CO and H2 production current densities, with 73 wt % Au at the low cathodic potential region (−0.6 to −0.9 VRHE). The suggested synergetic effect between both catalytic components underlines the promising character of this hybrid system and is expected to significantly add to the strategic production of syngas for subsequent applications.

Rapid synthesis of gold nanoparticles using silk fibroin: characterization, antibacterial activity, and anticancer properties

In the present work, well-dispersed gold nanoparticles (AuNPs) were synthesised by the reduction of HAuCl4.xH2O using silk fibroin as a reducing agent. UV-visible spectroscopy confirmed the formation of AuNPs by showing surface plasmon resonance (SPR) at 526–518 nm. The FT-IR study revealed that the hydroxyl groups in the Tyr residue and the carboxyl groups in the Asp and/or Glu residues were the most active functional groups for the conversion of Au ion reduction. The transmission electron microscope (TEM) images showed that the formed nanoparticles were uniformly embedded in the silk fibroin solution. The AuNPs are spherical in shape with smooth edges and around 5–8 nm in diameter. Also, these possess very good stability and dispersity and can be stored for a long period. Further, the X-ray diffraction (XRD) study confirmed the nanocrystalline phase of the gold with cubic crystal structure. The biogenic gold nanoparticles displayed antibacterial activity against Gram-positive and Gram-negative bacteria, and also showed promising anticancer properties.

A disposable aptasensing device for label-free detection of fumonisin B1 by integrating PDMS film-based micro-cell and screen-printed carbon electrode

A disposable aptasensing device for specific detection of fumonisin B1 (FB1), the most toxic of fumonisin B-series, has been fabricated. In this design, the pretreated screen-printed carbon electrode (SPCE) has been firstly covered by a polydimethylsiloxane (PDMS) film with a hole to construct a micro-cell with the conventional three electrodes at the bottom. Subsequently, well-dispersed gold nanoparticles (AuNPs) have been electrodeposited on the working electrodes to serve as excellent matrices for thiolated aptamer immobilization. Since a single nanoparticle could be conjugated with a large number of aptamer probe, the dense decoration of AuNPs on SPCE provided abundant binding sites for aptamer anchoring, finally enhancing the impedance signal effectively. A high affinity between FB1 and its aptamer has been demonstrated by a small association constant (Ka) of 1.19×109M−1 calculated by Langmuir adsorption isotherm. The developed aptasensor showed a good linearity in the range from 10pgmL−1 to 50ngmL−1 with a low detection limit of 3.4pgmL−1 (S/N=3). The developed aptasensing device is cost-effective, simple in operation, high-sensitive, less reagent consumption, and can be easily expand to other mycotoxins if the specific aptamer is available.

Well-dispersed gold nanoparticles anchored into thiol-functionalized hierarchically porous materials for catalytic applications

In this work, we demonstrate a novel method that enables the fabrication of thiol-functionalized hierarchically porous materials (SH-HPMs) by combination of hyper-cross-linking and molecular templating of core-shell bottlebrush copolymers. Well-dispersed gold (Au) nanoparticles with an average size of 3.0 nm, synthesized by in situ reduction of HAuCl4, were then anchored into the SH-HPMs support, which showed remarkable catalytic performances on the reduction reaction of 4-nitrophenol.

Fabrication of gold nanoparticles-decorated reduced graphene oxide as a high performance electrochemical sensing platform for the detection of toxicant Sudan I

In this paper, we are presenting a facile, green and in situ synthesis strategy for the convenient preparation of well-dispersed gold nanoparticles (AuNPs)-decorated reduced graphene oxide (RGO) without the use of any template molecules and poisonous reductant. The as-synthesized nanocomposite has been detailedly characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, thermogravimetric analysis as well as electrochemical technologies. The morphological and structural characterizations illustrate that AuNPs can be efficiently decorated on RGO with the Au content of 20.33wt% in the matrix and the size of the embedded AuNPs vary between 25 and 40nm. The electrochemical investigations confirm that the small-sized AuNPs on the RGO film can remarkably boost the electrocatalytic activity for the oxidation of Sudan I, which can be used as an enhanced electrochemical sensing platform for the sensitively detection of the toxicant Sudan I. Moreover, the kinetic parameter studies demonstrate that the Sudan I electro-oxidation at the AuNPs/RGO electrode is a diffusion-controlled process which involves two-electron and two-proton transfer. Under the optimal conditions, a wide linear range of Sudan I detection from 0.01 to 70μmolL−1 with good linearity (R2=0.9965, 0.9942) and a low detection limit (1.0nmolL−1, S/N=3) were obtained. In comparison with the existing analogues ever reported, the AuNPs/RGO eletrode exhibits overwhelmingly superior comprehensive properties for the sensitive detection of Sudan I. Finally, the newly developed sensor was applied to quantitative determination of Sudan I in food samples such as chilli powder and ketchup sauce with satisfactory sensitivity, selectivity and reversibility.