Attached Au Nanoparticles Research Articles

Surface Plasmon Resonance Enhanced Photoelectrochemical Sensing of Cysteine Based on Au Nanoparticle-Decorated ZnO@graphene Quantum Dots.

In this work, Au nanoparticle-decorated ZnO@graphene core-shell quantum dots (Au-ZnO@graphene QDs) were successfully prepared and firstly used to modify an ITO electrode for the construction of a novel photoelectrochemical biosensor (Au-ZnO@graphene QDs/ITO). Characterization of the prepared nanomaterials was conducted using transmission electron microscopy, steady-state fluorescence spectroscopy and the X-ray diffraction method. The results indicated that the synthesized ternary nanomaterials displayed excellent photoelectrochemical performance, which was much better than that of ZnO@graphene QDs and pristine ZnO quantum dots. The graphene and ZnO quantum dots formed an effective interfacial electric field, enhancing photogenerated electron-hole pairs separation and leading to a remarkable improvement in the photoelectrochemical performance of ZnO@graphene QDs. The strong surface plasmon resonance effect achieved by directly attaching Au nanoparticles to ZnO@graphene QDs led to a notable increase in the photocurrent response through electrochemical field effect amplification. Based on the specifical recognition between cysteine and Au-ZnO@graphene QDs/ITO through the specificity of Au-S bonds, a light-driven photoelectrochemical sensor was fabricated for cysteine detection. The novel photoelectrochemical biosensor exhibited outstanding analytical capabilities in detecting cysteine with an extremely low detection limit of 8.9 nM and excellent selectivity. Hence, the Au-ZnO@graphene QDs is a promising candidate as a novel advanced photosensitive material in the field of photoelectrochemical biosensing.

Enhanced photocatalytic activity through anchoring and size effects of Au nanoparticles on niobate nanotubes and nanosheets for water splitting

The inorganic semiconducting potassium hexaniobate (K4Nb6O17) has a wide band gap of 3.4 eV and has been widely studied as a photocatalyst activated by the ultraviolet part of the solar spectrum. In this study, we have prepared nanotubes and nanosheets of H4Nb6O17 and attached Au nanoparticles of two different sizes to both. The resultant composites are characterised and their activity towards H2 generation by photocatalytic water splitting is investigated. We found that the morphology of the nano-niobate had minimal effect for the Au particles attached directly to the niobate, however for the (3-Aminopropyl) triethoxysilane (APTES) anchored Au particles a marked difference in their activities towards water splitting was observed. The APTES-Au-nanosheets produced a maximum volume of hydrogen of 1384.3 μmol g−1 h−1, which was much higher than the 36.9 μmol g−1 h−1 for the parent niobate nanotubes. Morphology and different interaction were considered as the main factors affecting photocatalytic efficiency.

Enhanced thermoelectric performance of vertically aligned silicon nanowires through the cold spot effect and charge carrier trapping effect of attached gold nanoparticles

The thermoelectric performance of vertically aligned silicon (Si) nanowires (NWs) with diameters of 100–150 nm fabricated through metal-assisted chemical etching is improved using electroless-deposited gold (Au) nanoparticles (NPs) (ф ≈ 10 nm). After the deposition of metal NPs, the thermal conductivity and Seebeck coefficient of the Si NWs decrease 5.78-fold and increased 2.71-fold, respectively. Despite the 3.23-fold increase in the electric resistivity of Si NWs through the deposition of Au NPs, the figure of merit of the Au NP-deposited Si NWs is enhanced by 1320% (0.444) compared to that of pristine Si NWs (0.0337). The power factor is enhanced 2.28-fold after Au NP deposition (0.175–0.400 mV·K−2m−1). Based on finite-element method simulations of Au NP-deposited Si NW, a cold spot is generated inside the Si NW by the attached Au NP. Moreover, charge carrier trapping at the interface between the Si NW and Au NP is anticipated due to interfacial Fermi-level pinning. Cold spot and charge carrier trapping effects are proposed as important factors for enhancing the thermoelectric performance of Au NP-deposited Si NWs.

Exotic carbon nanotube based field effect transistor for the selective detection of sucrose

A carbon nanotube decorated with Au nanoparticles (Au-CNTs) could be an active sensing element of a field-effect transistor (FET) for the sensitive detection of sucrose among the sugar family (glucose, fructose and sucrose). The sensor showed high sensitivity for sucrose (0.64 mM−1) up to 2.5 mM, but it showed extremely low sensitivity for glucose (~0.28 mM−1) and fructose (~0.05 mM−1). The origin of the selective detection mechanism might be the increased potential barrier between the conductive CNTs by the adsorption of the bulky sucrose on the surface of the attached Au nanoparticles. We demonstrated that the Au-CNT-FET could be a good biosensor for the fast and easy detection of sucrose level among the concentrated sugar mixture in a honey and a sports drink within acceptable error range in food industry, ~1%.

Non-enzymatic and non-invasive glucose detection using Au nanoparticle decorated CuO nanorods

Non-enzymatic electrochemical glucose sensors have been fabricated using hydrothermally grown CuO nanorods on fluorine doped tin oxide (FTO) coated glass substrates. The sensing performance has been increased by several times after attaching Au nanoparticles with CuO nanorods. The formation of CuO nanorods and attachment of Au nanoparticles were confirmed using scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) study. The Au decorated CuO nanorod electrodes demonstrated glucose sensitivity of 2009 μAmM-1 cm-2, in the linear detection range 5 μM to 1.325 mM, with detection limit of 0.17 μM. Such Au decorated sensing electrodes are highly selective and exhibited long-term stability. Non-invasive glucose detection has been demonstrated using human saliva samples. The sensitivity of the sensor for salivary glucose detection was found to be 1740 μAmM-1 cm-2. Our present study demonstrated the promising use of Au decorated CuO NR electrodes for low cost, non-enzymatic, non-invasive diabetes monitoring application.

Plasmon mediated enhancement and tuning of optical emission properties of two dimensional graphitic carbon nitride nanosheets

We demonstrate surface plasmon induced enhancement and tunablilty in optical emission properties of two dimensional graphitic carbon nitride (g-C3N4) nanosheets through the attachment of gold (Au) nanoparticles. Raman spectroscopy has revealed surface enhanced Raman scattering that arises due to the combined effect of the charge transfer process and localized surface plasmon induced enhancement in electromagnetic field, both occurring at the nanoparticle–nanosheet interface. Photoluminescence studies suggest that at an optimal concentration of nanoparticles, the emission intensity can be enhanced, which is maximum within the 500–525 nm region. Further, the fabricated electroluminescent devices reveal that the emission feature can be tuned from bluish-green to red (∼160 nm shift) upon attaching Au nanoparticles. We propose that the π*→π transition in g-C3N4 can trigger surface plasmon oscillation in Au, which subsequently increases the excitation process in the nanosheets and results in enhanced emission in the green region of the photoluminescence spectrum. On the other hand, electroluminescence of g-C3N4 can induce plasmon oscillation more efficiently and thus can lead to red emission from Au nanoparticles through the radiative damping of particle plasmons. The influence of nanoparticle size and coverage on the emission properties of two dimensional g-C3N4, nanosheets has also been studied in detail.

Influence of Au nanoparticles on luminescence property of YF3 submicrostructures doped with Yb3+ and Ho3+ (Eu3+) ions

Orthorhombic phase YF3 submicrostructures doped with Yb3+ and Ho3+ (Eu3+) ions (YF3:RE3+ (RE3+ = Yb3+, Ho3+ (Eu3+)) submicrostructures) were synthesized by a coprecipitation method and decorated with Au nanoparticles (NPs) to form hybrid submicrostructures. It was found that the attached Au NPs on the surfaces of YF3:RE3+ submicrostructures could generate localized electromagnetic (EM) field with high density, which enable the enhancement of upconversion luminescence emission of YF3:RE3+. The luminescence emission of Eu3+ ion was employed to investigate the local symmetry change of YF3:RE3+ after Au NPs were introduced to the system. The possible mechanism of Au NPs on the luminescence property of doped rare earth (RE) ions was proposed and discussed. These submicrostructures may find potential applications in phosphors and solar cells.

Carbon Nanodot Surface Modifications Initiate Highly Efficient, Stable Catalysts for Both Oxygen Evolution and Reduction Reactions

Efficient, stable, and low‐cost electrocatalysts for the oxygen evolution and reduction reactions (OER and ORR) are essential components of energy conversion. Although much progress has been achieved in the development of platinum‐based electrocatalysts for ORR and iridium‐based electrocatalysts for OER, they are still not yet viable for large‐scale commercialization because of the high cost and scanty supply of the noble metals. Here, it is demonstrated that carbon nanodots surface‐modified with either phosphorus or amidogen can respectively achieve electrocatalytic activity approaching that of the benchmark Pt/C and IrO2 /C catalysts for ORR and OER. Furthermore, phosphorus (amidogen)‐modified carbon nanodots with attached Au nanoparticles exhibit superior ORR (OER) activity better than commercial Pt/C (IrO2/C) catalysts as well as excellent electrochemical stability under visible light.

Efficiency enhance the photoluminescence of ZnO nanowires array by the surface plasmonic effect of Au nanoparticles

Attaching Au nanoparticles to nanowires is an important approach to enhance the properties of photoelectric nano-devices based on ZnO nanowires array. We carry out a systematic investigation on affection of the Au nanoparticles size to the photoluminescence of ZnO nanowire array. Different sizes of Au nanoparticles range from 8 nm to 20 nm distinguished by 2 nm are synthesised by a method combining spurting and annealing. The green emission is quenched effectively and the UV emission of ZnO nanowires array is enhanced drastically, which is consistent with the wavelength-dependent generation of surface plasmon. We also find that 10 nm is the optimise size of Au nanoparticles to furthest enhance the UV emission of the ZnO nanowires array. This method can improve the photoelectric properties of ZnO based nano-devices conveniently and economically.

Enhanced performances of nonenzymatic glucose sensors by attaching Au nanoparticles onto the surfaces of Cu2O@Cu nanocable arrays

Nanoarchitectures (Au–Cu2O@CuNCs) have been fabricated successfully for the first time by attaching Au nanoparticles onto the surfaces of Cu2O@Cu nanocables. The hybrid material nanoelectrodes exhibit highly enhanced performances in detecting glucose nonenzymatically, compared to those made with Cu2O@Cu nanocable arrays or Au nanoparticles.

On‐line surface enhanced Raman spectroscopic detection in a recyclable Au@SiO2 modified glass capillary

A facile method was developed to fabricate a high sensitive, reproducible and recyclable surface enhanced Raman spectroscopy (SERS) active glass capillary. The Au nanoparticles were synthesized through a seed‐mediated growth approach and then self‐assembled onto the inner wall of glass capillaries. The attached Au nanoparticles were homogeneously coated with thin silica shell by using the silane coupling agent to functionalize the Au surface. By using thiophenol (TP) as SERS probe molecules, the substrate exhibited robust SERS effects. The adsorbed SERS probe molecules could be rapidly and completely removed away by flowing sodium borohydride solution and thus to obtain a refresh Au@SiO2 film‐coated substrate for the cyclic detection on different species. The on‐line detection of TP and malachite green (MG) with different concentrations was performed in the flowing system. The intensities of SERS signals were dependent on concentrations of the detected molecules. The results indicated that the SERS‐active substrate has potential applications on the on‐line qualitative and quasi‐quantitative analysis. Copyright © 2014 John Wiley & Sons, Ltd.

Broadband absorption enhancement of thin SOI photodiode with high-density gold nanoparticles

We demonstrated the quantum efficiency (QE) of silicon-on-insulator (SOI) photodiode was enhanced in visible wavelength region by using gold (Au) nanoparticles. The photons plasmonically scattered by Au nanoparticles couples with the waveguide mode in SOI, and are absorbed efficiently. Optimum size and density of Au nanoparticles have been investigated by 3-D FDTD simulations for sensitivity improvement. The highest enhancement factor of the absorption efficiency in 100-nm-thick SOI is obtained by periodically attaching Au nanoparticles of about 140 nm in diameter and 1.7 × 109 particles/cm2 in density. Two-fold enhancement in QE was experimentally achieved in visible by the SOI photodiode with randomly arranged Au nanoparticles of the size and density close to the optimized values.

Origin of enhanced photocatalytic activity and photoconduction in high aspect ratio ZnO nanorods

Faceted ZnO nanorods with different aspect ratios were synthesized by a solvothermal method by tuning the reaction time. Increased reaction leads to the formation of high aspect ratio ZnO nanorods largely bound by the prism planes. The high aspect ratio rods showed significantly higher visible light photocatalytic activity when compared to the lower aspect ratio structures. It is proposed that the higher activity is due to better charge separation in the elongated 1D structure. In addition, the fraction of unsaturated Zn(2+) sites is higher on the {1010} facets, leading to better adsorption of oxygen-containing species. These species enhance the production of reactive radicals that are responsible for photodegradation. The photocurrent for these ZnO nanostructures under solar light was measured and a direct correlation between photocurrent and aspect ratio was observed. Since the underlying mechanisms for photodegradation and photocurrent generation are directly related to the efficiency of electron-hole creation and separation, this observation corroborates that the charge separation processes are indeed enhanced in the high aspect ratio structures. The efficiency of photoconduction (electron-hole pair separation) could be further improved by attaching Au nanoparticles on ZnO, which can act as a sink for the electrons. This heterostructure exhibits a high chemisorption of oxygen, which facilitates the production of highly reactive radicals contributing to the high photoreactivity. The suggested mechanisms are applicable to other n-type semiconductor nanostructures with important implications for applications relating to energy and the environment.

Quenching of Confined C480 Dye in the Presence of Metal-Conjugated γ-Cyclodextrin

Here we demonstrate the designing of new optical-based materials having nanotubular γ-CD aggregates linked by coumarin 480 dyes: Au nanoparticles for light harvesting system. It is found that the fluorescence quenching of the coumarin 480 dye increases from 79 to 99% due to confinement of the dye inside γ-CD. The formation of the nanotubular structure of C480/CD complex is confirmed by fluorescence anisotropy decay and TEM study. The average decay times of the C480 dye inside γ-CD in the absence and presence of attached Au nanoparticles are 4.77 and 1.91 ns, respectively, and the rate constant of ET is found to be 3.13 × 108 s−1.

Plasmonic modulation of the upconversion fluorescence in NaYF4 :Yb/Tm hexaplate nanocrystals using gold nanoparticles or nanoshells.

Automatic upgrade: attachment of gold nanoparticles (NPs) onto upconversion nanocrystals (NCs) results in plasmonic interactions that lead to a significant enhancement of upconversion emission of more than 2.5. Conversely, formation of a gold shell greatly suppresses the NC emission because of considerable scattering of excitation irradiation (see picture; a=NC before seed attachment; b, c=NC with attached Au NPs; c=NC with Au shell; scale bar=50 nm).

Synthesis and Characterization of Carbon Nanotubes Decorated with Gold Nanoparticles

In presented work we report results of simple and viable method for producing Au/CNT composites. Chemical composition and crystallographic structure of the Au/CNT composites was confirmed by X-ray diffraction measurements, while transmission and scanning electron microscopy were used to characterize the morphology of nanocrystals as well as the distribution of nanocrystals in the composite. The obtained particles with relatively small diameter (less than 9 nm) were found to be spatially well dispersed on the carbon nanotubes. The density of attached Au nanoparticles is not sufficient, and cannot be improved by simple increasing gold loading.

Energy Transfer between Confined Dye and Surface Attached Au Nanoparticles of Mesoporous Silica

Nanoscale architectures have been designed by entrapping rhodamine 6G dye molecules into the channels of mesoporous silica and Au nanoparticles anchor onto the surface of the mesoporous matrix. The surface energy transfer between confined dye and Au nanoparticles has been studied by steady state and time-resolved spectroscopy. The appearance of second surface plasmon band at 680 nm with increasing the concentration of mesoporous silica indicates the formation of self-assembled structure of Au nanoparticles which is established by TEM and DLS studies. A mechanism for self-assembled Au nanoparticles is proposed. The PL quenching (76.3% to 27.4%) and energy transfer efficiency (51.8% to 17.4%) can be tuned with changing the arrangement of Au nanoparticles. Analysis reveals that the energy transfer from dye to Au nanoparticles is a surface energy transfer process and it follows 1/d4 distance dependence. This anisotropy decay reveals that the dye molecules are aligned inside the channels of mesoporous silica. Such energy transfer between confined dye and Au nanoparticles could pave the way for designing new optical based materials for the application in chemical sensing or light harvesting system.

Surface functionalization of single-walled carbon nanotubes using metal nanoparticles

Surface functionalization of suspended single-walled carbon nanotubes (SWNTs) using metal (Au) nanoparticles (NPs) is reported. SWNTs are grown on three-dimensionally patterned substrates by thermal chemical vapor deposition and successfully functionalized with Au NPs. Ethylendiamine is mainly used to functionalize SWNTs surface with amino groups before introducing Au NPs. From Raman scattering spectroscopy of the Au-functionalized suspended SWNTs, enhanced Raman scattering properties are obtained. The results suggest that the attached Au NPs may contribute to the enhancement of resonant phenomena. By measuring the electric properties after each functionalization process, it is found that Au NPs act as electron acceptor to the amine functionalized SWNTs.

Tailoring the photoluminescence of ZnO nanowires using Au nanoparticles

Rational design of hybrid nanostructures through attaching nanowires with nanoparticles isan effective route to enhance the existing functionalities or to explore new ones. We carryout a systematic investigation on the photoluminescence of ZnO nanowire–Aunanoparticle hybrid nanostructures synthesized by attaching Au nanoparticles ontoZnO nanowires. Citrate-stabilized 40 nm Au nanoparticles effectively quench thegreen emission and enhance the UV emission of the ZnO nanowires, which isconsistent with the wavelength-dependent generation of surface plasmon. TheUV/green emission intensity ratio could be reversibly and reproducibly tailored by attaching/detachingAu nanoparticles. This enhancement of UV emission diminishes if the Au nanoparticles arecoated with a polymer layer. We also find that the orange-red emission of the ZnOnanowires is related to the excess oxygen on the ZnO surface, and it is also tunable viaannealing and surface modifications.

Attachment of Gold Nanograins onto Colloidal Magnetite Nanocrystals

The successful attachment of 2−3 nm gold particles to ∼10 nm Fe3O4 nanocrystals through a simple, two-step chemically controlled procedure is reported. The surface of individual, relatively monodisperse, Fe3O4 nanospheres forming a stable colloidal methanolic solution is coated with an amino-terminated silane, peptized to induce positive charges on the particles' surfaces and then treated with a colloidal solution of negatively charged Au nanoparticles. A detailed investigation by transmission electron microscopy, X-ray diffraction, UV−vis, inductively coupled plasma, and superconducting quantum interference device magnetometry was performed in order to elucidate the morphology and properties of the nanocomposites. Due to their low concentration and small size of the attached Au particles, the optical properties are not observable in the case of the Fe3O4/Au nanocomposites. Additionally, the colloidal Fe3O4/Au nanocomposites are highly stable against separation and exhibit magnetic properties similar to those of the parent Fe3O4 nanocrystals. These novel nanoarchitectures open up new opportunities for the use of magnetite nanoparticles for in-vivo biomedical applications through chemical bonding of bioactive molecules to the attached Au nanoparticles.