Improving functional properties of ZnO nanostructures by transition-metal doping: role of aspect ratio

Localized surface plasmon resonance (LSPR) of gold nanoparticles (AuNPs) has been used for biosensing and chemical sensing applications because the LSPR peak wavelength depends on the dispersion state and local refractive index of the surrounding medium. In this study, AuNP-loaded silica gels were prepared as sensing chips with high transparency and solution holding capability. The silica gels were prepared at various sintering temperatures from 500 to 900 °C, and the AuNPs precipitated in the gels by using a subsequent thermal reduction process. At sintering temperatures of 700, 800, and 900 °C, transparent and crack-free AuNP-loaded silica gels were obtained. Transmission electron microscopy observation revealed the AuNP size to be approximately 20 nm, and they were highly dispersed in all the silica gel samples. However, the sintering temperature of the silica gels strongly affected the LSPR property of the AuNPs and the porous property of the silica gel. The samples sintered at higher temperature exhibited a lower LSPR sensing ability against the refractive index of immersing solvents. The low sensing ability was considered as a result of a decrease in the contact area between the AuNPs and immersing solvent caused by an increase in the silica gel density with sintering temperature.     

Characterization of gas-expanded liquid-deposited gold nanoparticle films on substrates of varying surface energy

Dodecanethiol-stabilized gold nanoparticles (AuNPs) were deposited via a gas-expanded liquid (GXL) technique utilizing CO(2)-expanded hexane onto substrates of different surface energy. The different surface energies were achieved by coating silicon (100) substrates with various organic self-assembled monolayers (SAMs). Following the deposition of AuNP films, the films were characterized to determine the effect of substrate surface energy on nanoparticle film deposition and growth. Interestingly, the critical surface tension of a given substrate does not directly describe nanoparticle film morphology. However, the results in this study indicate a shift between layer-by-layer and island film growth based on the critical surface tension of the capping ligand. Additionally, the fraction of surface area covered by the AuNP film decreases as the oleophobic nature of the surfaces increases. On the basis of this information, the potential exists to engineer nanoparticle films with desired morphologies and characteristics.     

Thermally annealed gold nanoparticles for surface-assisted laser desorption ionisation–mass spectrometry of low molecular weight analytes

Metal nanomaterials have an emerging role in surface-assisted laser desorption ionisation-mass spectrometry (SALDI-MS) providing a useful tool to overcome some limitations intrinsically related to the use of conventional organic matrices in matrix-assisted LDI-MS. In this contribution, the possibility to use a stainless-steel-supported gold nanoparticle (AuNP) film as a versatile platform for SALDI-MS was assessed. A sacrificial anode electrosynthetic route was chosen in order to obtain morphologically controlled core-shell AuNPs; the colloidal AuNPs were, thereafter, drop cast onto a stainless-steel sample plate and the resulting AuNP film was thermally annealed in order to improve its effectiveness as LDI-MS promoter. Spectroscopic characterization of the nanostructured film by X-ray photoelectron spectroscopy was crucial for understanding how annealing induced changes in the surface chemistry and influenced the performance of AuNPs as desorption/ionisation promoter. In particular, it was demonstrated that the post-deposition treatments were essential to enhance the AuNP core/analyte interaction, thus resulting in SALDI-MS spectra of significantly improved quality. The AuNP films were applied to the detection of three different classes of low molecular weight (LMW) analytes, i.e. amino acids, peptides and LMW polymers, in order to demonstrate the versatility of this nanostructured material.     

Immunoassay of plasmonic gold‐nanoparticle clusters: Plasmon coupling effects for Parkinson biomarker detection

A simple signal‐on plasmonic optical assay for the detection of the Parkinson biomarker using gold‐nanoparticle clusters (AuNCs) for signal amplification is presented. This approach is based on the improvement of the optical density (OD) change of the plasmonic band of a localized surface plasmon resonance (LSPR) Au nanoparticle (AuNP) sensor interface using Au NCs conjugated antibodies. The amplification results in a 260‐fold improvement in concentration detection, from 1,000 ng/mL (unlabeled antibody) to 3.8 ng/mL (antibody‐conjugated AuNCs). The sensitivity enhancement can be ascribed to the further plasmonic coupling between the antibody‐conjugated AuNCs and the AuNPs on the LSPR interface and the enhanced amount of target molecule bound to the bioassay. This AuNCs‐assisted signal amplification strategy allows for improving the sensitivity of the plasmon‐based bioassays and can be extended to other optical‐based diagnostic technologies. Importantly, the simple detecting procedure and protocol assembly make it competitive with other existing sensing technologies such as ELISA, allowing for practical usage in clinical diagnostics.     

Site-selective assembly and reorganization of gold nanoparticles along aminosilane-covered nanolines prepared on indium-tin oxide

We have fabricated gold nanoparticle (AuNP) arrays on indium-tin oxide (ITO) substrates in a nearly one-dimensional fashion. AuNPs were site-selectively immobilized on ITO of which the surface had been patterned by a nanolithography process based on scanning probe microscopy. The fabricated nanoscale lines covered with aminosilane self-assembled monolayer served as chemisorption sites for citrate-stabilized AuNPs of 20 nm in diameter, accordingly, AuNP nanolines with a thickness of single nanoparticle diameter were spontaneously assembled on the lines. In this 1D array, the AuNPs were almost separated from each other due to the electrostatic repulsion between their negatively charged surface layers. Furthermore, a reorganization process of the immobilized AuNP arrays has been successfully demonstrated by replacing each AuNP's surface layer from citric acid to dodecanethiol. By this process, the AuNPs lost their electrostatic repulsion and became hydrophobic so as to be attracted to each other through hydrophobic interaction, resulting in reorganization of the AuNP array. By repeating the deposition and reorganization cycle, AuNPs were more densely packed. The optical absorption peak of the arrays due to their plasmonic resonance was found to shift from 526 to 590 nm in wavelength with repeating cycles, indicating that the resonance manner was changed from the single nanoparticle mode to the multiple particle mode with interparticle coupling.     

Analysis of immunoreaction with localized surface plasmon resonance biosensor

The localized surface plasmon resonance (LSPR)-based optical biosensor was used as a potential tool for label-free detection of immunoreaction. The glass substrate covered with the self-assembled monolayer (SAM) of gold colloids was used widely in the sensors. Here, the glass substrate was modified by chemical hydroxylation first, and then gold colloids were immobilized on the substrate by electrostatic adsorption. The LSPR spectra were obtained on UV–vis absorption spectrometer. The specificity was examined by extensive nonspecific binding tests. The resonance condition on the local dielectric environment enables a simple form of molecular sensing. The binding of analyte to the biosensor surface causes a change in the absorbance which was responsive to the concentration of human IgG. So, the LSPR sensing yields similar results to the SPR technique, yet with much simpler instrument.     

Long Distance Electron Transfer Across >100 nm Thick Au Nanoparticle/Polyion Films to a Surface Redox Protein

Glutathione‐decorated 5 nm gold nanoparticles (AuNPs) and oppositely charged poly(allylamine hydrochloride) (PAH) were assembled into {PAH/AuNP}_n films fabricated layer‐by‐layer (LbL) on pyrolytic graphite (PG) electrodes. These AuNP/polyion films utilized the AuNPs as electron hopping relays to achieve direct electron transfer between underlying electrodes and redox proteins on the outer film surface across unprecedented distances >100 nm for the first time. As film thickness increased, voltammetric peak currents for surface myoglobin (Mb) on these films decreased but the electron transfer rate was relatively constant, consistent with a AuNP‐mediated electron hopping mechanism.     

Size-dependence enhancement in electrocatalytic activity of NiHCF-gold nanocomposite: potential application in electrochemical sensing

A nanocomposite of nickel hexacyanoferrate (NiHCF) was made with gold nanoparticles (AuNPs) of two different sizes (20 and 80 nm as AuNP(red) and AuNP(blue) respectively), synthesized via 3-glycidoxypropyltrimethoxysilane mediated reduction of 3-aminopropyltrimethoxysilane treated gold chloride and characterized by scanning electron microscopy and UV-VIS spectroscopy. The size of AuNPs was found to influence the two pairs of reversible voltammetric peaks of cation rich and cation deficient NiHCF. Such influence was identified from cyclic voltammetry of nanocomposite modified electrodes and applications during electrochemical sensing of two different analytes hydrazine and glutathione (GSH). Electrochemical sensing of hydrazine was based on cyclic voltammetry and differential pulse voltammetry (DPV) found as a function of sodium deficient NiHCF and was greatly amplified with increasing AuNPs nanogeometry. NiHCF alone is not an efficient electrode material for GSH analysis at the level required, however, the presence of AuNPs introduces size dependent sensitive and selective detection of GSH. GSH sensing based on linear sweep voltammetry (LSV) was found to be mediated by the potassium rich form of NiHCF redox couple in the presence of AuNPs. The results justified electrochemical detection of these analytes based on a mediated mechanism and support the role of AuNPs for facilitated electrochemical activity of NiHCF based systems as a function of nanogeometry.     

金纳米粒子的二步电解合成及表面增强拉曼散射活性研究

在超声条件下采用二步电解方法在十六烷基三甲基溴化铵/丙酮/水三组分体系中合成金纳米粒子. 首先采用恒电流或电位的阶跃方法, 使体系中生成较小的金纳米粒子并作为晶种; 接着采用电位双阶跃方法, 使金纳米粒子在原来基础上继续生长, 控制电解电量可获得不同大小的金纳米粒子. 通过静电作用在洁净的单晶硅片表面组装金纳米粒子, 获得具有不同形貌的硅片, 并以此作为表面增强拉曼散射基底, 以吡啶为探针分子, 研究了不同基底的表面增强拉曼散射活性, 结果表明吡啶谱峰强弱与纳米粒子在硅片表面的排列形貌有关.     

Gold nanoparticle-embedded porous graphene thin films fabricated via layer-by-layer self-assembly and subsequent thermal annealing for electrochemical sensing

A uniform three-dimensional (3D) gold nanoparticle (AuNP)-embedded porous graphene (AuEPG) thin film has been fabricated by electrostatic layer-by-layer assembly of AuNPs and graphene nanosheets functionalized with bovine serum albumin and subsequent thermal annealing in air at 340 °C for 2 h. Scanning electron microscopy (SEM) investigations for the AuEPG film indicate that an AuNP was embedded in every pore of the porous graphene film, something that was difficult to achieve with previously reported methods. The mechanism of formation of the AuEPG film was initially explored. Application of the AuEPG film in electrochemical sensing was further demonstrated by use of H(2)O(2) as a model analyte. The AuEPG film-modified electrode showed improved electrochemical performance in H(2)O(2) detection compared with nonporous graphene-AuNP composite film-modified electrodes, which is mainly attributed to the porous structure of the AuEPG film. This work opens up a new and facile way for direct preparation of metal or metal oxide nanoparticle-embedded porous graphene composite films, which will enable exciting opportunities in highly sensitive electrochemical sensors and other advanced applications based on graphene-metal composites.     

Iminodiacetic acid-functionalized gold nanoparticles for optical sensing of myoglobin via Cu2+ coordination

A novel gold nanoparticle (AuNP)-based optical sensing system has been developed for the detection of myoglobin (Mb), which is of significant importance for early disease diagnosis. Two thiol molecules containing an iminodiacetic acid moiety (IDA) were synthesized. This detection is based on the Mb-induced aggregation of IDA-functionalized AuNPs resulting from the structures of Mb sandwiched between the functionalized AuNPs via Cu(2+) bridges in the coordination interactions of IDA-Cu(2+)-histidine residues available on the Mb surface, which was confirmed by UV-vis spectroscopy, transmission electron microscopy, dynamic light scattering, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The induction aggregation resulted in a red shift in plasmon resonance band of the AuNPs concomitant with a change in solution color from red to purple. The qualitative and quantitative detections of Mb can be achieved by colorimetric observations and UV-vis spectral measurements, respectively. The selectivity of protein assay with the functionalized AuNPs was further investigated, and it is found that the optical sensing of histidine-rich proteins is closely related to number and distribution of surface histidine residues as well as size of proteins.     

AuNPs/PNIPAM复合颗粒的制备及其温敏性质

将金纳米颗粒(AuNPs)组装到聚N-异丙基丙烯酰胺(PNIPAM)水凝胶微球表面制备出AuNPs/PNIPAM复合颗粒. 将PNIPAM 凝胶的温敏特性与AuNPs的光学性质结合, 通过改变温度调节AuNPs的局部表面等离子共振(LSPR)吸收峰位置. 研究结果表明, 温度升高使AuNPs的LSPR吸收峰发生红移, 并且这种效应是可逆的. 同时发现, AuNPs的光学性质还可以作为表征PNIPAM水凝胶微球温敏行为的一种手段. 利用透射电镜、紫外-可见光谱仪及动态光散射仪对AuNPs/PNIPAM复合颗粒的形貌、光学性质、粒径变化等进行了分析.     

Reactive capture of gold nanoparticles by strongly physisorbed monolayers on graphite

Anthracene Diels Alder adducts (DAa) bearing two long side chains (H-(CH₂)₂₂O(CH₂)₆OCH₂-) at the 1- and 5-positions form self-assembled monolayers (SAMs) at the phenyloctane - highly oriented pyrolytic graphite (HOPG) interface. The long DAa side chains promote strong physisorption of the monolayer to HOPG and maintain the monolayer morphology upon rinsing or incubation in ethanol and air-drying of the substrate. Incorporating a carboxylic acid group on the DAa core enables capture of 1-4 nm diameter gold nanoparticles (AuNPs) provided (i) the monolayer containing DAa-carboxylic acids is treated with Cu²⁺ ions and (ii) the organic coating on the AuNP contains carboxylic acids (11-mercaptoundecanoic acid, MUA-AuNP). AuNP capture by the monolayer proceeds with formation of Cu²⁺ - carboxylate coordination complexes. The captured AuNP appear as mono- and multi-layered clusters at high coverage on HOPG. The surface density of the captured AuNPs can be adjusted from AuNP multi-layers to isolated AuNPs by varying incubation times, MUA-AuNP concentration, the number density of carboxylic acids in the monolayer, the number of MUA per AuNP, and post-incubation treatments.     

Flower-like self-assembly of gold nanoparticles for highly sensitive electrochemical detection of chromium(VI)

We report here the fabrication of a flower-like self-assembly of gold nanoparticles (AuNPs) on a glassy carbon electrode (GCE) as a highly sensitive platform for ultratrace Cr(VI) detection. Two AuNP layers are used in the current approach, in which the first is electroplated on the GCE surface as anchors for binding to an overcoated thiol sol–gel film derived from 3-mercaptopropyltrimethoxysilane (MPTS). The second AuNP layer is then self-assembled on the surface of the sol–gel film, forming flower-like gold nanoelectrodes enlarging the electrode surface. When functionalized by a thiol pyridinium, the fabricated electrode displays a well-defined peak for selective Cr(VI) reduction with an unusually large, linear concentration range of 10–1200 ng L⁻¹ and a low detection limit of 2.9 ng L⁻¹. In comparison to previous approaches using MPTS and AuNPs on Au electrodes, the current work expands the use of AuNPs to the GCE. Subsequent functionalization of the secondary AuNPs by a thiol pyridinium and adsorption/preconcentration of Cr(VI) lead to the unusually large detection range and high sensitivity. The stepwise preparation of the electrode has been characterized by electrochemical impedance spectroscopy (EIS), scanning electronic microscopy (SEM), and IR. The newly designed electrode exhibits good stability, and has been successfully employed to measure chromium in a pre-treated blood sample. The method demonstrates acceptable fabrication reproducibility and accuracy.     

Effect of amino,hydroxyl, and carboxyl terminal groups of alkyl chains of self-assembled monolayers on the adsorption pattern of gold nanoparticles

The adsorption pattern of gold nanoparticles (AuNPs) on functionalized self-assembled monolayers (SAMs) produced on a Au(111) surface was characterized. The Au(111) was modified with 11-amino-1-undecanethiol hydrochloride (AUT), 11-mercapto-1-undecanol (MUT), or 11-mercaptoundecanoic acid (MUA) at an elevated temperature and pressure. The AuNPs aggregated on the AUT-SAM surface, whereas they were well dispersed on the MUT-SAM surface and localized on the MUA-SAM surface. The results suggest that interactions between AuNPs differ according to the degree of peeling of citrate-layer-capped AuNPs. The degree of peeling, which is related to both the surface randomness of the SAMs and the functional characteristics of the terminal group of each SAM, was discussed on the basis of scanning tunneling microscopy observations, X-ray photoelectron spectroscopic analyses, and contact angle measurements. Our study shows that AuNP patterns can be controlled by changing the terminal group of the alkyl thiol SAM on a Au(111) surface.     

Multi-technique Characterization of Self-assembled Carboxylic Acid Terminated Alkanethiol Monolayers on Nanoparticle and Flat Gold Surfaces

Gold nanoparticles (AuNPs) with 14, 25 and 40nm diameters were functionalized with different chain length (C6, C8, C11 and C16) carboxylic acid terminated alkanethiol self-assembled monolayers (COOH-SAMs). X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were used to examine the changes in surface chemistry as both AuNP diameter and SAM chain length were varied. COOH-SAMs on flat gold surfaces were also examined and compared to the COOH-SAM on AuNP results. For a given surface, as the COOH-SAM chain length increased the XPS C/Au atomic ratio increased due to an increased number of carbon atoms per molecule in the overlayer and an increased attenuation of the Au substrate signal. For the C16 COOH-SAMs, as the size of AuNPs decreased the XPS C/Au atomic ratio and the apparent SAM thickness increased due to the increased curvature of the smaller AuNPs. The C16 COOH-SAMs on the flat Au had the lowest XPS C/Au atomic ratio and apparent SAM thickness of any C16 COOH-SAM covered Au surface. The effective take-off angles of the COOH-SAMs were also calculated by comparing the apparent thickness of COOH-SAMs with literature values. The effective take-off angle for C16 COOH-SAM on 14nm, 25nm and 40nm diameter AuNPs and flat Au were found to be 57°, 53°, 51° and 39°, respectively, for data acquired in a mode that collects a wide range of photoelectron take-off angles. The effective take-off angle for C16 COOH-SAM on 14nm AuNP and flat Au decreased to 52° and 0°, respectively, for data acquired in a mode that collects a narrow range of photoelectron take-off angles. The ToF-SIMS results showed similar changes in surface chemistry with COOH-SAM chain length and AuNP size. For example, the ratio of the sum of the C(1-4)H(x)O(y) positive ion intensities to the sum of the Au-containing positive ions intensities increased with decreasing AuNP size and increasing COOH-SAM chain length. Fourier transform IR spectroscopy in the attenuated total reflectance mode (FTIR-ATR) was used to characterize the crystallinity of the COOH-SAMs. The CH(2) stretching frequencies decreased with increasing COOH-SAM chain length on flat Au. The C16 COOH-SAM on the 14nm AuNPs exhibited a crystalline-like CH(2) stretching frequency. The size, size distribution, shapes and solution stability of AuNPs were investigated with transmission electron microscopy (TEM) and UV/VIS spectroscopy. As the average diameter of the AuNPs decreased the size distribution became narrower and the shape became more spherical.     

Fabrication and electrochemical application of three-dimensional gold nanoparticles: self-assembly

Multilayers film of nanostructured citrate-stabilized gold particles (AuNPs) has been fabricated based on the layer-by-layer (LBL) technique using a self-assembled monolayer of 1,4-benzenedimethanethiol (BDMT). The formation of AuNPs and BDMT self-assemblies as alternative multilayers was confirmed by transmission electron microscopy (TEM), X-ray photoelectron spectroscope (XPS), and quartz crystal microbalance (QCM). The formation of uniform AuNP layers with an average monolayer thickness of 5-6 nm was obvious in the TEM images. The existence of BDMT molecules as cross linkers for the AuNPs' layers was proved by XPS measurements. The greater affinity of AuNPs' layers to bind BDMT molecules in comparison with the bare Au bulk electrode was revealed by QCM measurements. Electrochemically, the AuNPs' layers on the electrode surface did not only catalyze the reduction of oxygen (ca. 100-mV positive shift of the reduction peak potential compared with that at the bare Au bulk electrode) but also showed a fascinating nature of working as a renewed activated-electrode surface; a zigzag response was observed for oxygen reduction during alternative immobilization of BDMT and the AuNP layer. The self-assembly of a new AuNPs layer restored the catalytic activity that was entirely blocked by the preceding BDMT layer.     

An ultrasensitive hydrogen peroxide biosensor based on electrocatalytic synergy of graphene–gold nanocomposite, CdTe–CdS core–shell quantum dots and gold nanoparticles

We first reported an ultrasensitive hydrogen peroxide biosensor in this work. The biosensor was fabricated by coating graphene–gold nanocomposite (G–AuNP), CdTe–CdS core–shell quantum dots (CdTe–CdS), gold nanoparticles (AuNPs) and horseradish peroxidase (HRP) in sequence on the surface of gold electrode (GE). Cyclic voltammetry and differential pulse voltammetry were used to investigate electrochemical performances of the biosensor. Since promising electrocatalytic synergy of G–AuNP, CdTe–CdS and AuNPs towards hydrogen peroxide was achieved, the biosensor displayed a high sensitivity, low detection limit (S/N = 3) (3.2 × 10⁻¹¹ M), wide calibration range (from 1 × 10⁻¹⁰ M to 1.2 × 10⁻⁸ M) and good long-term stability (20 weeks). Moreover, the effects of omitting G–AuNP, CdTe–CdS and AuNP were also examined. It was found that sensitivity of the biosensor is more 11-fold better if G–AuNP, CdTe–CdS and AuNPs are used. This could be ascribed to improvement of the conductivity between graphene nanosheets in the G–AuNP due to introduction of the AuNPs, ultrafast charge transfer from CdTe–CdS to the graphene sheets and AuNP due to unique electrochemical properties of the CdTe–CdS, and good biocompatibility of the AuNPs for horseradish peroxidase. The biosensor is of best sensitivity in all hydrogen peroxide biosensors based on graphene and its composites up to now.     

Multifunctional covalently stabilized vesicles acting simultaneously as the template of gold nanoparticle cluster and the nanocarrier of guest molecules

The terminal hydroxyl groups of amphiphilic multiarm star copolymers with a hydrophilic hyperbranched polyethylenimine (PEI) core and hydrophobic poly(ε-caprolactone) (PCL) arms were partially or completely transformed into the radical-crosslinkable methacrylate (MA) groups (PEI-b-PCL-MA). The resulting PEI-b-PCL-MA polymers with 100% MA substitution self-assembled in water into simple vesicles, whereas those with partial MA substitution aggregated into complex vesicles. These structures could be proved by transmission electron microscopy and dynamic light scattering only after crosslinking the intra-vesicular MA groups that generated the covalently stabilized vesicles (CSVs). The obtained CSVs could be used as host for the formation of gold nanoparticle (AuNP) cluster, and the AuNP clusters stabilized by the CSVs were stable under a wider range of CSV/AuNP feed ratio than those stabilized by the uncrosslinked precursors. The diameter of AuNPs in the clusters was in the range of 4-6 nm, and the distance of adjacent AuNPs could be modulated through altering the feed ratio of CSV/AuNP. The color of the solutions of AuNPs with CSV could be tuned from brown to red, purple, even blue. The composites of CSV and AuNPs could be further used as nanocarriers to accommodate hydrophobic guest of pyrene, and a higher amount of AuNPs in the nanocarriers led to a lower encapsulation capacity for pyrene guests.     

The fabrication of stable gold nanoparticle-modified interfaces for electrochemistry

Forming stable gold nanoparticle (AuNP)-modified surface is important for a number of applications including sensing and electrocatalysis. Herein, tethering AuNPs to glassy carbon (GC) surfaces using surface bound diazonium salts is investigated as a strategy to produce stable AuNP surfaces. GC electrodes are first modified with 4-aminophenyl (GC-Ph-NH(2)), and then the terminal amine groups are converted to diazonium groups by incubating the GC-Ph-NH(2) interface in NaNO(2) and HCl solution to form a 4-phenyl diazonium chloride-modified interface (GC-Ph-N(2)(+)Cl(-)). Subsequently AuNPs are immobilized on the interface by electrochemical reduction to give a 4-phenyl AuNP-modified interface (GC-Ph-AuNP). For comparison, 4-aminophenyl AuNP- and 4-thiophenol AuNP-modified GC interfaces (GC-Ph-S-AuNP and GC-Ph-NH-AuNP), in which AuNPs are tethered to the surfaces by forming S-Au and NH-Au bond, respectively, were also prepared. Cyclic voltammetry, electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy are used to characterize these fabricated interfaces. The AuNP on GC-Ph-AuNP surfaces demonstrate good stability under sonication in Milli-Q water, during electrochemical treatment in 0.05 M H(2)SO(4) solution, and over several weeks. By contrast, the GC-Ph-NH-AuNP and GC-Ph-S-AuNP surfaces showed significant particle losses under equivalent conditions.