Electrochemical Measurement of Gold Oxide Reduction and Methods for Acid Neutralization and Minimization of Water in Wet Ionic Liquid

The formation and reduction of gold oxide in wet ionic liquid (IL), N‐trimethyl‐N‐butylammonium bis(trifluoromethanesulfonyl)imide, ([Me₃NⁿBu][TFSI]) is examined. The water concentration is determined using both the charge and peak current from the reduction of gold oxide and compared directly with Karl Fischer data. The quantitative determination of water in the IL is demonstrated for concentrations between 0.09 and 0.74 by weight (w%). The treatment of wet IL with dry nitrogen or molecular sieves reduces the water below background levels. Finally, methods for acid neutralization and the reduction of water with molecular sieves are conducted to minimize their impact on subsequent electrochemical measurements.     

Determination of Norepinephrine Alone and in the Presence of Ascorbic and Uric Acids Using a Gold Electrode Modified with Gold Nanoparticles and Self‐Assembled Layers of meso‐2,3‐Dimercaptosuccinic Acid

This paper reports on the modification of gold electrodes with self‐assembled layers (SAMs) composed of meso‐2,3‐dimercaptosuccinic acid, cysteamine and gold nanoparticles, respectively and their application to quantitative determination of norepinephrine alone and in the presence of ascorbic and uric acids in solution at pH 7. The modification was carried out on two kinds of templates: a bare gold electrode (2D electrode) and a gold electrode coated in the first step with gold nanoparticles (3D electrode). Cyclic voltammograms reveal an enhancement of the norepinephrine electrooxidation in comparison to a bare, (non‐modified) gold electrode. The oxidation peaks for norepinephrine, ascorbic acid and uric acid have a peak‐to‐peak separation that enables their selective determination even in a complex mixture.     

新形金纳米片的简单制备与生长机制

在室温(~30 ℃)条件下,氯金酸(HAuCl₄)均匀混合在粘稠的表面活性剂聚乙烯吡咯烷酮(PVP)胶体(水为溶剂)中,HAuCl₄可以被PVP还原,从而形成纳米片. 本工作中,通过调整晶体生长条件,成功合成了大量新形貌的单晶金纳米片(厚度数十纳米,尺寸为数个微米). 例如,在晶体生长初期阶段,通过引入温度变化(如降温10-20 ℃),形成的金纳米片主要是六角星形,并伴有盾状、内凹外凸的三角状、截角的、三叉的及多台阶等新形纳米片. 结合理论计算,阐明了金纳米片的生长机制：在一定条件下,金(111)晶面不仅可以沿着<110>方向生长成为常规的三角或六角纳米片,还可以沿<211>、<321>等不同方向生长成含有更高指数侧面的新形金纳米片.     

Gold nanoparticle decorated graphene oxide/silica composite stationary phase for high‐performance liquid chromatography

In the initial phase of this study, graphene oxide (GO)/silica was fabricated by assembling GO onto the silica particles, and then gold nanoparticles (GNPs) were used to modify the GO/silica to prepare a novel stationary phase for high‐performance liquid chromatography. The new stationary phase could be used in both reversed‐phase chromatography and hydrophilic interaction liquid chromatography modes. Good separations of alkylbenzenes, isomerides, amino acids, nucleosides, and nucleobases were achieved in both modes. Compared with the GO/silica phase and GNPs/silica phase, it is found that except for hydrophilicity, large π‐electron systems, hydrophobicity, and coordination functions, this new stationary phase also exhibited special separation performance due to the combination of 2D GO with zero‐dimensional GNPs.     

Gold & silver nanoparticles supported on manganese oxide: Synthesis,characterization and catalytic studies for selective oxidation of benzyl alcohol

Nano-gold and silver particles supported on manganese oxide were synthesized by the co-precipitation method. The catalytic properties of these materials were investigated for the oxidation of benzyl alcohol using molecular oxygen as a source of oxygen. The catalyst was calcined at 300, 400 and 500 °C. They were characterized by electron microscopy, powder X-ray diffraction (XRD) and surface area. It was observed that the calcination temperature affects the size of the nanoparticle, which plays a significant role in the catalytic process. The catalyst calcined at 400 °C, gave a 100% conversion and >99% selectivity, whereas catalysts calcined at 300 and 500 °C gave a conversion of 69.51% and 19.90% respectively, although the selectivity remains >99%.     

Upconversion nanoparticle-based fluorescence resonance energy transfer assay for Cr(III) ions in urine

A novel assay of chromium(III) ion based on upconversion fluorescence resonance energy transfer was designed and established. Lysine-capped NaYF₄:Yb/Er upconversion nanoparticles (UCNPs) and dimercaptosuccinic acid-capped gold nanoparticles (AuNPs) were used as the energy donor and acceptor, respectively. They were bound together via electrostatic interaction, resulting in the quenching of the fluorescence of UCNPs by AuNPs. Chromium(III) ions can specifically and strongly interact with dimercaptosuccinic acid that was modified on the surface of AuNPs, leading to the separation of AuNPs from UCNPs and the recovery of fluorescence of UCNPs. The fluorescence recovery of UCNPs showed a good linear response to Cr³⁺ concentration in the range of 2–500 nM with a detection limit of 0.8 nM. This method was further applied to determine the levels of Cr³⁺ in urine. Compared with other fluorescence methods, current method displayed very high sensitivity and signal-to-noise ratio because of the excitation of near-infrared that can eliminate autofluorescence, providing a promising examination of biological samples for the diagnostic purposes.     

A high-throughput homogeneous immunoassay based on Förster resonance energy transfer between quantum dots and gold nanoparticles

A novel homogeneous immunoassay based on Förster resonance energy transfer for sensitive detection of tumor, e.g., marker with carcinoembryonic antigen (CEA), was proposed. The assay was consisted of polyclonal goat anti-CEA antibody labeled luminescent CdTe quantum dots (QDs) as donor and monoclonal goat anti-CEA antibody labeled gold nanoparticles (AuNPs) as acceptor. In presence of CEA, the bio-affinity between antigen and antibody made the QDs and AuNPs close enough, thus the photoluminescence (PL) quenching of CdTe QDs occurred. The PL properties could be transformed into the fluorometric variation, corresponding to the target antigen concentration, and could be easily monitored and analyzed with the home-made image analysis software. The fluorometric results indicated a linear detection range of 1–110 ng mL⁻¹ for CEA, with a detection limit of 0.3 ng mL⁻¹. The proposed assay configuration was attractive for carcinoma screening or single sample in point-of-care testing, and even field use. In spite of the limit of available model analyte, this approach could be easily extended to detection of a wide range of biomarkers.     

Thorough tuning of the aspect ratio of gold nanorods using response surface methodology

In the present work a central composite design based on response surface methodology (RSM) is employed for fine tuning of the aspect ratios of seed-mediated synthesized gold nanorods (GNRs). The relations between the affecting parameters, including ratio of l-ascorbic acid to Au³⁺ ions, concentrations of silver nitrate, CTAB, and CTAB-capped gold seeds, were explored using a RSM model. It is observed that the effect of each parameter on the aspect ratio of developing nanorods highly depends on the value of the other parameters. The concentrations of silver ions, ascorbic acid and seeds are found to have a high contribution in controlling the aspect ratios of NRs. The optimized parameters led to a high yield synthesis of gold nanorods with an ideal aspect ratio ranging from 1 (spherical particle) to 4.9. In addition, corresponding tunable surface Plasmon absorption band has been extended to 880 nm. The resulted nanorods were characterized by UV–visible spectrometry and transmission electron microscopy.     

Species selective preconcentration and quantification of gold nanoparticles using cloud point extraction and electrothermal atomic absorption spectrometry

The determination of metallic nanoparticles in environmental samples requires sample pretreatment that ideally combines pre-concentration and species selectivity. With cloud point extraction (CPE) using the surfactant Triton X-114 we present a simple and cost effective separation technique that meets both criteria. Effective separation of ionic gold species and Au nanoparticles (Au-NPs) is achieved by using sodium thiosulphate as a complexing agent. The extraction efficiency for Au-NP ranged from 1.01 ± 0.06 (particle size 2 nm) to 0.52 ± 0.16 (particle size 150 nm). An enrichment factor of 80 and a low limit of detection of 5 ng L⁻¹ is achieved using electrothermal atomic absorption spectrometry (ET-AAS) for quantification. TEM measurements showed that the particle size is not affected by the CPE process. Natural organic matter (NOM) is tolerated up to a concentration of 10 mg L⁻¹. The precision of the method expressed as the standard deviation of 12 replicates at an Au-NP concentration of 100 ng L⁻¹ is 9.5%. A relation between particle concentration and the extraction efficiency was not observed. Spiking experiments showed a recovery higher than 91% for environmental water samples.     

Highly sensitive detection of human cardiac myoglobin using a reverse sandwich immunoassay with a gold nanoparticle-enhanced surface plasmon resonance biosensor

A highly sensitive reverse sandwich immunoassay for the detection of human cardiac myoglobin (cMb) in serum was designed utilizing a gold nanoparticle (AuNP)-enhanced surface plasmon resonance (SPR) biosensor. First, a monoclonal anti-cMb antibody (Mab1) was covalently immobilized on the sensor surface. AuNPs were covalently conjugated to the second monoclonal anti-cMb antibody (Mab2) to form an immuno-gold reagent (Mab2-AuNP). The reverse sandwich immunoassay consists of two steps: (1) mixing the serum sample with Mab2-AuNP and incubation for the formation of cMb/Mab2-AuNP complexes and (2) sample injection over the sensor surface and evaluation of the Mab1/cMb/Mab2-AuNP complex formation, with the subsequent calculation of the cMb concentration in the serum. The biosensor signal was amplified approximately 30-fold compared with the direct reaction of cMb with Mab1 on the sensor surface. The limit of detection of cMb in a human blood serum sample was found to be as low as 10 pM (approx. 0.18 ng mL⁻¹), and the inter-assay coefficient of variation was less than 3%. Thus, the developed SPR-based reverse sandwich immunoassay has a sensitivity that is sufficient to measure cMb across a wide range of normal and pathological concentrations, allowing an adequate estimation of the disease severity and the monitoring of treatment.