Au NP Research Articles

Catalytic reduction of 4-nitrophenol with gold nanoparticles stabilized by large-ring cyclodextrins

Au NP, stabilized by large-ring cyclodextrins, proved to be efficient for the catalytic reduction of 4-nitrophenol.

Ultrafine gold nanoparticle embedded poly(diallyldimethylammonium chloride)–graphene oxide hydrogels for voltammetric determination of an antimicrobial drug (metronidazole)

In this work, gold nanoparticle (Au NP) decorated poly(diallyldimethylammonium chloride) (PDDA) functionalized graphene hydrogel (Au NP@PDDA/GH) nanocomposites were fabricated.

A rapid and ultrasensitive colorimetric biosensor based on aptamer functionalized Au nanoparticles for detection of saxitoxin.

Saxitoxin (STX) is one of the most important marine toxins which affects the safety of domestic water. Rapid, sensitive and selective recognition of STX is crucial in environment monitoring. Here, we demonstrate a facile and ultrasensitive colorimetric sensor based on gold nanoparticles (Au NPs) and aptamer (Au NPs-aptamer biosensor) for specific and quantitative detection of STX. The aptamer reacts specifically with STX, resulting in the aggregation of Au NPs and the color change of the Au NP solution. The lowest detection concentration of the colorimetric sensor is 10 fM (3 fg mL−1), and a good linear relationship (R2 = 0.9852) between the absorbance ratio and STX concentrations (10 fM to 0.1 μM) indicates that our Au NPs-aptamer biosensor can be used for quantitative sensing of STX. The detection time of STX is 30 minutes, and the sensor is successfully applied in the specific detection of STX in seawater. The Au NP-aptamer biosensor shows great potential in practical applications to monitor environmental pollution, marine aquaculture pollution, and seafood safety.

Influence of patch size and chemistry on the catalytic activity of patchy hybrid nonwovens.

In this work, we provide a detailed study on the influence of patch size and chemistry on the catalytic activity of patchy hybrid nonwovens in the gold nanoparticle (Au NP) catalysed alcoholysis of dimethylphenylsilane in n-butanol. The nonwovens were produced by coaxial electrospinning, employing a polystyrene solution as the core and a dispersion of spherical or worm-like patchy micelles with functional, amino group-bearing patches (dimethyl and diisopropyl amino groups as anchor groups for Au NP) as the shell. Subsequent loading by dipping into a dispersion of preformed Au NPs yields the patchy hybrid nonwovens. In terms of NP stabilization, i.e., preventing agglomeration, worm-like micelles with poly(N,N-dimethylaminoethyl methacrylamide) (PDMA) patches are most efficient. Kinetic studies employing an extended 1st order kinetics model, which includes the observed induction periods, revealed a strong dependence on the accessibility of the Au NPs' surface to the reactants. The accessibility is controlled by the swellability of the functional patches in n-butanol, which depends on both patch chemistry and size. As a result, significantly longer induction (tind) and reaction (tR) times were observed for the 1st catalysis cycles in comparison to the 10th cycles and nonwovens with more polar PDMA patches show a significantly lower tR in the 1st catalysis cycle. Thus, the unique patchy surface structure allows tailoring the properties of this “tea-bag”-like catalyst system in terms of NP stabilization and catalytic performance, which resulted in a significant reduction of tR to about 4 h for an optimized system.

Optimization and gas sensing properties of Au nanoparticle modified α-Fe2O3 nanodisk structures for highly sensitive acetone detection

Au nanoparticle (Au NP) modified α-Fe2O3 nanodisk structures are obtained using a facile hydrothermal method and annealing based surface treatment.

The role of adsorbed oleylamine on gold catalysts during synthesis for highly selective electrocatalytic reduction of CO2 to CO.

The low-coordinated sites of electrocatalysts favour hydrogen evolution, while the edge sites are active for CO2 reduction. Oleylamine is used to stabilize nanoparticles by adsorbing on the low-coordinated sites. The hydrogen evolution reaction was dramatically suppressed and the FECO remained >93% from -0.4 to -0.8 V (vs. RHE) when oleylamine ligands existed on the surface of a gold catalyst. More H+ and electrons were involved in the CO evolution reaction, which changed the rate-limiting step from single-electron transfer to the chemical reaction step. The results establish that the surface-adsorbed surfactants during catalyst synthesis have an important effect on CO2 electrocatalytic reduction.

Controlled Phase Behavior of Thermally Sensitive Poly(N-isopropylacrylamide/ionic liquid) with Embedded Au Nanoparticles.

We have synthesized a series of poly(N-isopropylacrylamide/ionic liquid) with deposited Au nanoparticles. The size of the nanoparticle range was varied from 10 to 35 nm, and these were characterized by transmission electron microscopy analysis. Ionic liquids (IL) were chosen by varying the polymerizable unit to be both in cationic (allyl) and anionic (acrylate) moiety. One-pot polymerization was done with N-isopropylacrylamide and IL using ammonium persulphate as the initiator, to which were added already prepared Au NPs. These thermally sensitive composites formed, possessed reversible swelling/deswelling abilities in water, and demonstrated a reversible visible phase transition, which was detected by differential scanning calorimetric measurements. The lower critical solution temperature (LCST) showed dependency on the size of nanoparticles and the IL independently. It was seen that the LCST of PNIPAM-based composite films can be tuned from 32 °C to a range of 23–67 °C by choosing the desired Au NP size, its concentration and kind of IL.

Gas-Phase Synthesis for Label-Free Biosensors: Zinc-Oxide Nanowires Functionalized with Gold Nanoparticles

Metal oxide semiconductor nanowires have important applications in label-free biosensing due to their ease of fabrication and ultralow detection limits. Typically, chemical functionalization of the oxide surface is necessary for specific biological analyte detection. We instead demonstrate the use of gas-phase synthesis of gold nanoparticles (Au NPs) to decorate zinc oxide nanowire (ZnO NW) devices for biosensing applications. Uniform ZnO NW devices were fabricated using a vapor-solid-liquid method in a chemical vapor deposition (CVD) furnace. Magnetron-sputtering of a Au target combined with a quadrupole mass filter for cluster size selection was used to deposit Au NPs on the ZnO NWs. Without additional functionalization, we electrically detect DNA binding on the nanowire at sub-nanomolar concentrations and visualize individual DNA strands using atomic force microscopy (AFM). By attaching a DNA aptamer for streptavidin to the biosensor, we detect both streptavidin and the complementary DNA strand at sub-nanomolar concentrations. Au NP decoration also enables sub-nanomolar DNA detection in passivated ZnO NWs that are resilient to dissolution in aqueous solutions. This novel method of biosensor functionalization can be applied to many semiconductor materials for highly sensitive and label-free detection of a wide range of biomolecules.

Photothermal effect of Au nanoparticles and photothermal inactivation to saccharomycetes cell

Au nanoparticles (Au NPs) absorb light energy and convert it to thermal energy that transfers to environment. The temperature variation of Au NP and environment as well as photothermal conversion efficiency of Au NP are problems concerned by researchers. Herein the linear absorption of Au NP is simulated based on Mie theory, the surface plasmon resonance peak wavelength increases with increase of NP diameter, and the absorption reaches the maximum when the diameter is 70 nm. The heat transfer from an Au NP to water is simulated by finite element method, the thermal influence space is shown to be a sphere with radius of dozens of nanometers. The increase of Au NP temperature is fast in initial stage and slow in later stage of irradiation, the NP temperature saturates with elapse of irradiation time. The photothermal conversion efficiency is determined to be 0.7. Thermal effect of Au NPs to saccharomycetes cell is investigated through laser irradiation at 532 nm, the cell that adheres Au NPs are found to be killed by photothermal effect, which shows application of Au NPs in photothermal therapy.

A signal-on fluorescence based biosensing platform for highly sensitive detection of DNA methyltransferase enzyme activity and inhibition.

DNA methylation mediated by DNA methyltransferase (MTase) enzyme is internal cell mechanism which regulate the expression or suppression of crucial genes involve in cancer early diagnosis. Herein, highly sensitive fluorescence biosensing platform was developed for monitoring of DNA Dam MTase enzyme activity and inhibition based on fluorescence signal on mechanism. The specific Au NP functionalized oligonucleotide probe with overhang end as a template for the synthesis of fluorescent silver nanoclusters (Ag NCs) was designed to provide the FRET occurrence. Following, methylation and cleavage processes by Dam MTAse and DpnI enzymes respectively at specific probe recognition site could resulted to release of AgNCs synthesizer DNA fragment and returned the platform to fluorescence signal-on state through interrupting in FRET. Subsequently, amplified fluorescence emission signals of Ag NCs showed increasing linear relationship with amount of Dam MTase enzyme at the range of 0.1-20 U/mL and the detection limit was estimated at 0.05 U/mL. Superior selectivity of experiment was illustrated among other tested MTase and restriction enzymes due to the specific recognition of MTase toward its substrate. Furthermore, the inhibition effect of applied Dam MTase drug inhibitors screened and evaluated with satisfactory results which would be helpful for discovery of antimicrobial drugs. The real sample assay also showed the applicability of proposed method in human serum condition. This novel strategy presented an efficient and cost effective platform for sensitive monitoring of DNA MTase activity and inhibition which illustrated its great potential for further application in medical diagnosis and drug discovery.

Hybrid film of single-layer graphene and carbon nanotube as transparent conductive electrode for organic light emitting diode

Single layer graphene as a transparent conductive electrode (TCE) suffers from high sheet resistance, low work function, and hydrophobicity. In this work, a hybrid TCE of single-layer graphene, carbon nanotube (CNT) and gold nanoparticles (Au NP) decoration is proposed. The hybridization of graphene with CNT enhances the electrical conductivity while maintaining its high transmittance. The Au NP decorated TCE shows a sheet resistance of ∼100 Ω/sq and transmittance of 96%. The potential of TCE is demonstrated in a solution-processed yellow organic light emitting diode (OLED). By introducing a thin layer of Al-doped zinc oxide between the Au NPs and graphene-carbon nanotube networks which increases the hydrophilicity of the surface, OLED with a current efficiency of ∼2.1 cd/A and a turn-on voltage of ∼5 V is obtained suggesting that this TCE can be a viable option for OLED-anode.

Effect of Hot-Electron Injection on the Excited-State Dynamics of a Hybrid Plasmonic System Containing Poly(3-hexylthiophene)-Coated Gold Nanoparticles

We investigated the photophysical interaction between a conjugated polymer (CP) and a plasmonic gold nanoparticle (Au NP) using transient absorption spectroscopy. We prepared a hybrid system contai...

The Fabrication of Rigid Crosslinker-Decorated Gold Nanoparticle Array Film for Catalyzing CO2 Cycloaddition

Abstract In order to precisely design the active sites in two-dimensional (2D) gold-based catalysts, we have developed a convenient and versatile plasma-assisted droplet evaporation-rigid crosslinking method for the fabrication of gold nanoparticle (Au NP) array film. Four kinds of Au NP arrays have been decorated respectively with rigid sulfurated crosslinkers i.e. thieno[3,2-b]thiophene, 2,2′-bithiophene, 1,4-benzenedithiol and 4,4′-thiodibenzenethiol, and the density of crosslinkers can be adjusted under plasma treatment. Particularly, the utilization of 4,4′-thiodibenzenethiol gave uniform particle sizes to form a periodical 2D structure, which provides multiple exposed active sites of gold nanoparticles rather than enwinding by the alkyl chains. Meanwhile, the weaker electron-donating effect and steric hindrance of rigid groups in the crosslinkers could also enhance the catalytic activity. In addition, the Au NP array film can be transferred from the glass substrate and further composited with polymers and metal organic framework (MOF) into self-standing composite membrane. Therefore, this rigid crosslinked array film can serve as an environmentally friendly catalyst for CO2 cycloaddition under atmospheric CO2 pressure, which offers a novel application of Au NPs array film, and opens up a new way for the design and fabrication of 2D hybrid materials.

Arbitrary Gold Nanoparticle Arrays Fabricated through AFM Nanoxerography and Interfacial Seeded Growth.

Based on arrays of Au seeds fabricated withatomicforce microscopy (AFM) nanoxerography, the seeded growth of gold nanoparticles (Au NPs) on surface is achieved. The size evolution of Au NPs in each spot is tracked by in situ AFM and SEM images because each spot can be easily localized in the array system. The extinction microspectra extracted in real time with enhanced signals and red-shift can further monitor the increasing size of Au NPs. As a powerful platform, AFM nanoxerography makes it easy to tune the spot size and the intervals among spots in the Au NP arrays without preparing a template. It also allows for fabricating arbitrary patterns including various symbols and graphs. More interestingly, the in situ growth of Au NPs offers an approach to decreasing the interparticle distance, and thus forming closely interconnected Au nanowire assembly, exhibiting immense potential in the nanoelectronic system.

Three-dimensional periodic structures of gold nanoclusters in the interstices of sub-100 nm polymer particles toward surface-enhanced Raman scattering

Regularly ordered polymer nanoparticle (PNP) assemblies incorporating gold nanoparticle (Au NP) clusters into the PNP interstices were fabricated by a simultaneous deposition of PNPs and Au NPs on a glass substrate. Monodisperse PNPs with an average size of 66 nm were employed as a template in the co-assembly to create the sub-100 nm periodic Au nanostructures on the substrate. First, mono-layering of PNP array with incorporation of 14 nm Au NPs was performed by a drop-casting to examine the number ratio of Au NPs to PNPs for multi-layering. Absorption spectra of the mono-layered co-assemblies of PNPs and Au NPs were employed to characterize the clustered state of Au NPs in the interstices of mono-layered PNPs. The number ratio suitable for homogeneous incorporation of Au NPs clustered in the interstice was found to be ranged from 6 to 8 in the characterization. Then, multi-layered co-assemblies of PNPs and clustered Au NPs were fabricated by a vertical deposition method with the Au NP number ratio of 8 to PNPs. Lifting rate of the substrate on which the PNPs were deposited was varied in the vertical deposition method to tune the film thickness of NP co-assembly. A decrease in the lifting rate to 1 μm/s could thicken the film to 0.71 μm corresponding to 13 layers of PNPs, resulting in the fabrication of periodic structures of Au NP clusters with a high packing density. Signal-to-noise ratio in the Raman measurement using p-mercaptobenzoic acid as a target molecule was successfully enhanced by multi-layering of the co-assembly, indicating that Au NP clusters were homogeneously incorporated into the interstices of PNPs in the co-assemblies.

Self-healing and high reusability of Au nanoparticles catalyst based on supramolecular hydrogel

In this work, supramolecular hydrogels were utilised as soft reactor for gold nanoparticles (Au NPs) to prepare cucurbit[8]uril (CB[8]) based supramolecular hydrogel loaded with Au NP(Au/CB[8] hydrogel) catalysts. The morphology and structure of the catalysts were characterized via UV–vis spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray powderdiffraction and thermo gravimetric analyzer analysis. The Au/CB[8] hydrogels were utilised as catalysts and reaction media for the reduction reactions of 4-nitrophenol (4-NP) with NaBH4 aqueous. The reduction rate constants at four temperatures (16 °C, 25 °C, 34 °C and 43 °C) and the activation parameters were calculated. The activation energy of 4-NP was 65.83 kJ mol−1. These types of hydrogel-composite catalyst systems exhibit self-healing and can be used repetitively up to seven times with 100% conversion and only 20% reduction in the initial reduction rate. This process provides a novel method for the production of highe fficiency and self-healing nanomaterals with various applications.

Ultrafast Relaxation Processes of Conjugated Polymer Nanoparticles in the Presence of Au Nanoparticles.

Considering the importance of conjugated polymer nanoparticles, major emphasis has been given for designing and understanding the energy transfer and charge transfer processes of organic-inorganic hybrids for light harvesting applications. In the present study, we have designed an aqueous solution-based light harvesting system using conjugated polymer nanoparticles (poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene], MEH-PPV) and Au nanoparticles. The change in photo-induced processes in the presence of metal nanoparticles are studied by steady-state absorption, time-resolved emission, time-resolved fluorescence up-conversion, ultrafast anisotropy and femtosecond transient absorption spectroscopy. Global and target analysis of transient absorption data validate the creation of a collective delocalized state in polymer nanoparticles, and the time scale for excitation energy funnelling from S1 state to low lying collective delocalized state (CLs ) is 18 ps. Then, the electron transfer from the CLs state to Au NP occurs with a time constant of 150 ps. The 815 ps long lived charge transfer (CT) state signifies the charge transfer from the CLs state of polymer nanoparticles to Au NP. Such basic understanding of relaxation processes in hybrid systems is very important for designing inorganic-organic hybrid light-harvesting systems.

Rational Design of Electrocatalytic Interfaces: Cd UPD Mediated Nitrate Reduction on Pd:Au Bimetallic Surfaces

INTRODUCTION Efforts in our laboratories have been focused on the rational design and assembly of bifunctional electrocatalytic interfaces incorporating two electrocatalysts acting in series as a means of improving both the overall activity and specificity of redox processes involving multiple transfer of electrons. This strategy was recently implemented to promote the reduction of NO3 - on Au NP dispersed on the surface of glassy carbon, GC, by adsorbed hemin (Hm), an iron porphyrin, in aqueous electrolytes containing Cd2+.1 This work represents an extension of this previous study in which Hm has been replaced by Pd nanoparticles, NP, co-dispersed with Au NP on GC, a tactic that virtually eliminates the formation of Au|Pd alloys. Impetus for this selection was provided by the much lower overpotential for NO2 - reduction on Pd compared to that on adsorbed Hm, a factor that would lead to overall activities surpassing those found earlier for the Cd(UPD)|Hm system. EXPERIMENTAL All electrochemical measurements were performed in an all-glass, three-compartment cell, filled with deaerated (Ar, Airgas, PP300) 0.1 M HClO4 solutions prepared from ultrapure perchloric acid (OmniTrace Ultra) and ultra-high purity water, UPW, generated by a Barnstead system (18.2 MΩ cm). A carbon rod (Alfa Aesar, diameter 6.15 mm) and a Ag/AgCl (Basi, MF2052) were used as counter and reference electrodes, respectively. Experiments were carried out with a GC disk electrode, GCE, (Pine Instruments, disk area, 0.196 cm2) using a commercial rotator (Pine Instruments, Model AFMSRX) and a Metrohm Autolab (PGSTAT302N). Cadmium perchlorate, Cd(ClO4)2 (Sigma-Aldrich, 99.999%), and sodium nitrate, NaNO3, (Sigma Aldrich, ACS reagent) were used as received. Nanoparticles, NP of Au and Pd were synthesized and cleaned using a methodology previously described in which an aqueous solution of the corresponding metallic precursor (HAuCl4 or H2PdCl4) was reduced with ice-cold and freshly prepared NaBH4 solution in the presence of trisodium citrate.2 Stock suspensions of each type of NP were prepared by mixing 1 volume of the original, as received, NP, with 3 volumes of UPW. To prepare either Au or Pd dispersions on the GCE, denoted hereafter as Au|GCE or Pd|GCE, 10 µL of the diluted NP aqueous suspensions were delivered to the GC surface using a micropipette, and then allowed to dry with a gentle stream of Ar. To prepare the co-dispersed Pd and Au NP on a GC disk, Pd:Au|GCE, 500 µL of each dilute NP suspension were mixed in a vial and following sonication, 10 µL of the mixture then delivered on the GCE using a micropipette, and allowed to dry under Ar. RESULTS AND DISCUSSION Shown in 1 are cyclic voltammograms recorded with Au|GCE (magenta), Pd|GCE (black) and Pd:Au|GCE (green) in pristine 0.1 N HClO4, displayed features believed to be characteristic of the metals involved. Integration of the characteristic reduction peaks in green in Fig 1 were found to be approximately half of those in either the Au|GCE or Pd|GCE (see magenta and black curves), and thus consistent with the relative amounts of each of the NP in the Pd:Au|GCE. Shown in Panel A, Fig. 2 are cyclic voltammograms obtained with these NP modified GCE surfaces in 0.1 M HClO4 containing 1 mM Cd(ClO4)2 and 2 mM NaNO3. Cursory inspection of these data reveals much higher activity for the Pd:Au|GCE, even though the amount of each NP was decreased to half, compared to the single metal surfaces. The same overall trend was found for measurements performed under forced convection, as shown in Panel B in this figure which reinforces the view that the two catalysts are indeed acting in series, i.e., Cd UPD on Au is responsible for the conversion of NO3 - to NO2 -, whereas Pd reduces NO2 - further to products of lower oxidation states. REFERENCES Y. Chen, H. Zhu, M. Rasmussen and D. Scherson, J. Phys. Chem. Lett., 1, 1907 (2010).C. M. Sanchez-Sanchez, F. J. Vidal-Iglesias, J. Solla-Gullon, V. Montiel, A. Aldaz, J. M. Feliu and E. Herrero, Electrochim. Acta, 55, 8252 (2010). ACKNOWLEDGEMENTS: This work was supported by a grant from NSF, CHE-1412060. Figure 1

Gold Nanoparticle Embedded Modified MWCNT Electrodes for Electrochemical Detection of Arsenic in Water

Email of corresponding author: dipban@iitg.ac.in : We focus on electrochemical detection of arsenite and/or arsenate in water using different kinds of electrodes made from gold nanoparticle embedded on substituted multiwall-carbon-nanotubes (MWCNT). The CNTs were functionalised with thiol groups by reaction with cysteamine. Following this, three different electrodes were fabricated using thiol substituted MWCNTs, gold nanoparticle (Au NP) embedded thiol substituted MWCNTs, and magnetite doped Au NP embedded MWCNTs. Subsequently, effect of Au NPs on the electrodes in the selectivity and sensitivity of the sensor was studied. The aforementioned experiments suggest that the affinity of the arsenite ions towards the thiol groups were found to be magnified by the integration of an optimal amount of Au NPs. Further, addition of magnetite particles in the CNT matrix made the sensor more sensitive towards arsenic detection. The working principles, mainly the change of the surface potential, of the electrodes were characterized by surface potential microscopy (SPOM) study using atomic force microscopy (AFM). The study helped in the miniaturization of the arsenic sensor using screen printed commercial electrode system with a modification of the working electrode based on requirement as stated before. Interestingly, we extracted the electrochemical response using an open source Arduino UNO based potentiostat unit, as shown in Fig. 1, to translate the concept into a portable electrochemical arsenic sensor. Keywords: Arsenite/Arsenate sensor, electrochemical, Screen printed electrode, Gold nanoparticle, Arduino UNO. Figure 1

(Invited) Ultrafast Exciton, Bi-Exciton and Trion Dissociation Dynamics in Metal@Semiconductor Hetero-Structure Interface

Multiexciton harvesting from semiconductor quantum dot has been a new approach for improving the semiconductor device efficiency which include quantum dot sensitized solar cells (QDSC) and photodetectors. Till date, not many reports are available where relation between exciton/multiexciton dissociation in metal−semiconductor nanohybrid system and boosting the power conversion efficiency (PCE) of QDSC are discussed. Herein we report a detailed spectroscopic investigation on the dissociation dynamics of i) exciton in Au@CdSe, ii) biexciton in Au@CIS (CuInS2) and, iii) trion in Au@2D-MoS2 utilizing both time-resolved PL and ultrafast transient absorption (TA) techniques. Ultrafast transient absorption studies suggest that in all the above three systems the ultrafast formation of exciton/bi-exciton/trion, which efficiently dissociates in Au-semiconductor nano-hybrid structures. Prior to the dissociation electrons are captured by Au NP in the nanohybrid from the conduction band of CdSe/CIS/2D-MoS2 nano-structures which is energetically higher than Fermi level of Au. Here we demonstrate the proof-of-concept in multi-electron dissociation which may provide a new approach for improving the efficiency in QDSSCs. These findings can be an efficient approaches towards the design and development of efficient solar cell and optoelectronic devices using the principles of multiexciton/trion generation and extracting them in metal-semiconductor nanohybrid system.