Ion-selective electrodes for gold and silver determination

Some new ion-selective electrodes for silver and gold are described. They are based on the ion-associate species formed by the cyanide, chloride or thiourea complexes of the metals, with hydrophobic anions or cations, as appropriate. The electrodes have been applied to the determination of gold and silver in various technological process solutions in industry.     

Activity enhancement of a screen-printed carbon electrode by modification with gold nanoparticles for glucose determination

We have successfully developed a highly sensitive electrochemical sensor strip for a home blood-sugar monitoring device by a single-step straightforward procedure. The strip consists of a pair of screen-printed carbon electrodes, which work as counter and working electrodes in the chronoamperometric mode. To remedy the poor electrochemical activity of the printed carbon electrode, a small amount of gold nanoparticles was immobilized on the electrode. In the presence of glucose oxidase, the electrode modified with 2-nm particles showed about a five times higher sensitivity for glucose oxidation than the bare printed carbon electrode, and there was a significant dependence of the current on the particle diameter. Based on these observations, we have elucidated the glucose oxidation mechanism, which is comprised of two key factors, i.e. (1) electron transfer between the gold particles, and (2) electronic coupling between the gold particles and glucose oxidase.     

Glassy carbon electrodes modified with gold nanoparticles for the simultaneous determination of three food antioxidants

Electrochemical behavior of three antioxidants: butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and butylated hydroquinone (TBHQ), was investigated at a glassy carbon electrode modified with gold nanoparticles (AuNPs/GCE). This electrode was characterized by scanning electron microscopy (SEM). The experimental results indicated that the modified electrode was strongly electroactive during the redox reactions of BHA, BHT and TBHQ, and this was confirmed by the observed increased redox peak currents and shifted potentials; in addition, the oxidation products of BHA and TBHQ were found to be the same. The experimental conditions were optimized and the oxidation peaks of BHA and BHT were clearly separated. Based on this, an electrochemical method was researched and developed for the simultaneous determination of BHA, BHT and TBHQ in mixtures with the use of first derivative voltammetry; the linear concentration ranges were 0.10–1.50 μg mL⁻¹, 0.20–2.20 μg mL⁻¹ and 0.20–2.80 μg mL⁻¹, and detection limits were 0.039, 0.080 and 0.079 μg mL⁻¹, for BHA, BHT and TBHQ, respectively. The proposed method was successfully applied for the analysis of the three analytes in edible oil samples.     

One-step synthesis of amino-dextran-protected gold and silver nanoparticles and its application in biosensors

A sensitive method for the detection of the lectin protein concanavalin A (Con A) was developed using amino-dextran (AD)-protected gold (AD-Au) and silver nanoparticles (AD-Ag) as sensitive optical probes. The AD-Au and AD-Ag nanoparticles were synthesized by directly applying amino-dextran as a reductive and protective reagent. The size of the nanoparticles could be altered by changing the molar ratio of AD to the metal salt. The amino-dextran bound to Con A by forming a 4:1 Au-Con A complex at neutral pH, and the nanoparticles were induced to aggregate by Con A. The absorption intensity of the nanoparticles decreased linearly with as the Con A concentration was increased from 3.85×10^–8 to 6.15×10^–7 M. The Au-Con A complex was dissociated by the disaccharide isomaltose, which has a higher affinities for Con A than Au; this competitive strategy could also be used to detect similar types of saccharides.     

金纳米粒子的表面修饰及生物应用进展

近年来纳米材料被广泛应用于生物医学、航空航天和精细化工等领域。构成纳米材料的纳米粒子具有小尺寸效应、表面效应和宏观量子隧道效应等性质。其中金纳米粒子由于其独特的荧光特性、良好的生物相容性和表面等离子共振等性质,被广大科研人员进行深入研究。例如,在生物医学领域,科研人员构建了一系列新型的金纳米比色传感器、光学探针及各类载药体系等。然而,目前金纳米粒子仍存在水分散性差、肾清除效率低和量子发射产率低等问题,限制了其广泛应用。因此,研究人员对金纳米粒子表面进行多样化修饰,从而能有效克服上述缺点。本文就目前主流配体表面修饰金纳米粒子的研究进展进行了详细总结,着重介绍了功能化金纳米粒子在生物成像、生物检测、生物治疗三方面的应用,最后对金纳米粒子的临床治疗机制的探索以及商业化的应用进行了展望,希望能为相关领域的研究者们提供新思路。     

CYP450 biosensors based on screen-printed carbon electrodes for the determination of cocaine

A new electrochemical method has been described and characterized for the determination of cocaine using screen-printed biosensors. The enzyme cytochrome P450 was covalently attached to screen-printed carbon electrodes. Experimental design methodology has been performed to optimize the pH and the applied potential, both variables that have an influence on the chronoamperometric determination of the drug. This method showed a reproducibility of 3.56% (n = 4) related to the slopes of the calibration curves performed in the range from 19 up to 166 nM. It has been probed the used of this kind of biosensors in the determination of cocaine in street samples, with an average capability of detection of 23.05 ± 3.53 nM (n = 3, α = β = 0.05).     

Electrochemical nanostructured biosensors: carbon nanotubes versus conductive and semi-conductive nanoparticles

The aim of this work was to demonstrate that various types of nanostructures provide different gains in terms of sensitivity or detection limit albeit providing the same gain in terms of increased area. Commercial screen printed electrodes (SPEs) were functionalized with 100 µg of bismuth oxide nanoparticles (Bi₂O₃ NPs), 13.5 µg of gold nanoparticles (Au NPs), and 4.8 µg of multi-wall carbon nanotubes (MWCNTs) to sense hydrogen peroxide (H₂O₂). The amount of nanomaterials to deposit was calculated using specific surface area (SSA) in order to equalize the additional electroactive surface area. Cyclic voltammetry (CV) experiments revealed oxidation peaks of Bi₂O₃ NPs, Au NPs, and MWCNTs based electrodes at (790 ± 1) mV, (386 ± 1) mV, and (589 ± 1) mV, respectively, and sensitivities evaluated by chronoamperometry (CA) were (74 ± 12) µA mM^?1 cm^?2, (129 ± 15) ±A mM^?1 cm^?2, and (54 ± 2) ±A mM^?1 cm^?2, respectively. Electrodes functionalized with Au NPs showed better sensing performance and lower redox potential (oxidative peak position) compared with the other two types of nanostructured SPEs. Interestingly, the average size of the tested Au NPs was 4 nm, under the limit of 10 nm where the quantum effects are dominant. The limit of detection (LOD) was (11.1 ± 2.8) ±M, (8.0 ± 2.4) ±M, and (3.4 ± 0.1) ±M for Bi₂O₃ NPs, Au NPs, and for MWCNTs based electrodes, respectively.     

Surface modification of gold electrodes with anthraquinone diazonium cations

Electrochemical grafting of anthraquinone (AQ) groups to gold electrodes was carried out in acetonitrile (ACN) and in aqueous acidic media (0.05 M H₂SO₄). For the first time, the covalent attachment of AQ to gold is demonstrated. Electrochemical quartz crystal microbalance (EQCM), atomic force microscopy (AFM) and cyclic voltammetry (CV) were used to characterise the AQ-modified Au electrodes. Electrografting from both solutions containing the corresponding diazonium salt yielded a strongly attached AQ layer. AFM examination showed that a multilayer AQ film was formed. The CV behaviour of the modified electrodes was tested in 0.1 M KOH and a quasi-reversible response was observed.     

基于碳纳米管修饰电极检测有机磷农药的生物传感器

报道了一种用于检测有机磷农药的安培型生物传感器,利用戊二醛交联法将乙酰胆碱酯酶和牛血清白蛋白固定在羧基化多壁碳纳米管修饰玻碳电极表面,制备了可应用于检测有机磷农药的新型生物传感器,并确定了最佳工作条件.该方法具有良好的重现性和回收率,当辛硫磷及氧化乐果的浓度分别在5.0×10-4～5.0×10-1 g/L和1.0×10-3～5.0×10-1 g/L范围内时,抑制率与其浓度的对数呈线性关系,检出限按抑制率为10%时的农药浓度计算,可分别达到3.6×10-4 g/L和5.9×10-4 g/L.     

Bare gold nanoparticles mediated surface-enhanced Raman spectroscopic determination and quantification of carboxylated single-walled carbon nanotubes

The paper proposes a simple and portable approach for the surface enhanced Raman scattering (SERS) spectroscopy in situ determination of carboxylated single walled carbon nanotubes (SWNTs) in river water samples. The method is based on the subsequent microfiltration of a bare gold nanoparticles solution and the water sample containing soluble carbon nanotubes by using a home-made filtration device with a small filtration diameter. An acetate cellulose membrane with a pore size of 0.2 μm first traps gold nanoparticles to form the SERS-active substrate and then concentrates the carbon nanotubes. The measured SERS intensity data were closely fit with a Langmuir isotherm. A portable Raman spectrometer was employed to measure SERS spectra, which enables in situ determination of SWNTs in river waters. The limit of detection was 10 μg L⁻¹. The precision, for a 10 mg L⁻¹ concentration of carbon nanotubes, is 1.19% intra-membrane and 10.5% inter-membrane.     

Formation of efficient catalytic silver nanoparticles on carbon nanotubes by adenine functionalization

Stuck together: Adenine/carbon nanotube hybrids trigger the formation of controlled-size catalytic silver nanoparticles on the nanotube surface. The catalytic efficiency of the resulting species was assessed in the oxidation of 2-methylhydroquinone to its corresponding benzoquinone, with complete recovery and without loss of activity of the catalyst.     

Preparation and electrocatalytic properties of gold nanoparticles loaded carbon nanotubes

Here, we report a new method of preparation of gold nanoparticles loaded carbon nanotubes (Au/CNTs) and the eleltrocatalystic properties of the obtained Au/CNTs as composite catalyst. This method shows advantages as it is easy to wash sodium citrate and the particle size of Au nanoparticles could by controlled by pH.     

基于多壁碳纳米管和纳米金修饰电极测定特殊序列DNA的电化学生物传感器的制备

基于多壁碳纳米管和纳米金复合膜修饰电极制备了特殊序列的靶DNA的电化学生物传感器.该传感器以六氨基合钌为杂交指示剂,用差示脉冲伏安法进行检测DNA杂化,其响应信号与靶DNA浓度在1.0×10<'-12>～1.0×10<'-7>mol/L范围内呈线性关系,检测限达3.5×10<'-13>mol/L.该传感器能区分单碱基错配的靶DNA.     

Deposition of gold nanoparticles onto thiol-functionalized multiwalled carbon nanotubes

Gold nanoparticles were deposited on the surface of multiwalled carbon nanotubes (MWNTs) functionalized with aliphatic bifunctional thiols (1,4-butanedithiol, 1,6-hexanedithiol, 1,8-octanedithiol, and 2-aminoethanethiol) through a direct solvent-free procedure. Small gold particles, with a narrow particle size distribution around 1.7 nm, were obtained on 1,6-hexanedithiol-functionalized MWNTs. For MWNTs functionalized with the aminothiol, the average Au particle size was larger, 5.5 nm, apparently due to a coalescence phenomenon. Gatan image filter (GIF) observations show that sulfur is at the nanotube surface with a non-homogeneous distribution. A higher sulfur concentration was observed around the gold nanoparticles' location.     

Disposable paper-based electrochemical sensor based on stacked gold nanoparticles supported carbon nanotubes for the determination of bisphenol A

This work reports a new type of disposable electrochemical sensor for the determination of bisphenol A (BPA). The working electrodes were fabricated by sputtering gold nanoparticles on commercial art paper and then modifying the gold layer with multi-walled carbon nanotubes (MWCNTs). The electrode in their intermediated and final stage was characterized by atomic force microscope, scanning electron microscope and electrochemical techniques. To perform electrochemical analysis, the resulting electrode was integrated with a homemade paper-based analytical device, which could also ensure the immobilization of MWCNTs on the electrode surface without any functionalization. The determination of BPA was investigated by linear sweep voltammetry (LSV). A wide linearity in the range from 0.2 to 20 mg/L with a detection limit of 0.03 mg/L (S/N = 3) was obtained. The between-sensor reproducibility was 5.7% (n = 8) for 0.5 mg/L BPA. The proposed sensor showed good resistance against interferences and was applied to detect BPA leached from real plastic samples with satisfying results. This disposable sensor is readily mass-produced and has been verified to serve as an attractive alternative to screen-printed electrodes for practical applications.     

Thermal behavior of carbon nanotubes decorated with gold nanoparticles

Three different forms of carbon, i.e., multi-walled carbon nanotubes (CNTs), single-walled CNTs, and soot, were decorated with gold nanoparticles by a new method. In this method C₁₀H₈ ⁻ ions transfer electrons to the CNTs or soot. These electrons on the carbon surface can then reduce Au³⁺ species to form supported Au nanoparticles with a narrow particle size distribution. Thermogravimetric/differential thermal analyses (TG/DTA), XRD, Raman, and TEM show that naphthalene molecules remain trapped inside the Au nanoparticles and can only be removed by treatment at ca. 300 °C. Remarkable effect of the Au nanoparticles on the oxidation of carbon by O₂ is also observed by TG/DTA, i.e., on-set oxidation temperature and activation energy (E _a). It is shown that as the Au particle size decreases from 25 to 2 nm a linear decrease of the oxidation temperature is observed. Au particles larger than 25 nm do not produce any significant effect on carbon oxidation. These results are discussed in terms of spillover catalytic effect where Au nanoparticles activate O₂ molecules to produce active oxygen species which oxidize the different carbon supports.     

The growth of uncoated gold nanoparticles on multiwalled carbon nanotubes

The growth of uncoated gold nanoparticles on the surface of multiwalled carbon nanotubes (MWCNTs) through the UV irradiation method was investigated. TEM observations showed that the size and the growth behavior of nanoparticles were primarily affected by the diameter of MWCNTs and solution pH values. The possible mechanisms were also discussed.     

Enzymeless determination of cholesterol using gold and silver nanoparticles as electrocatalysts

We present the results of synthesis and study of the electrocatalytic activity of gold and silver nanoparticles of different composition (individual metals, core–shell particles, nanoalloys, and particles synthesized electrochemically), immobilized on the surface of a glassy carbon electrode, with respect to cholesterol. A surfactant (cetyltrimethylammonium bromide) is selected to create an aqueous–organic emulsion of cholesterol. It is demonstrated that nanoparticles with a gold core and a silver shell with the regression equation of I = 1.4 × 10^–5 c _chol + 5.8 × 10^–5 (R ² = 0.97) and silver nanoparticles synthesized electrochemically with the regression equation of I = 1.0 × 10^–5 c _chol + 3.0 × 10^–4 (R ² = 0.95) possess optimal electrocatalytic characteristics.     

Seed-mediated synthesis of copper nanoparticles on carbon nanotubes and their application in nonenzymatic glucose biosensors

In this paper, for the first time, Cu nanoparticles (CuNPs) were prepared by seed-mediated growth method with Au nanoparticles (AuNPs) playing the role of seeds. Carbon nanotubes (CNTs) and AuNPs were first dropped on the surface of glassy carbon (GC) electrode, and then the electrode was immersed into growth solution that contained CuSO₄ and hydrazine. CuNPs were successfully grown on the surface of the CNTs. The modified electrode showed a very high electrochemical activity for electrocatalytic oxidation of glucose in alkaline medium, which was utilized as the basis of the fabrication of a nonenzymatic biosensor for electrochemical detection of glucose. The biosensor can be applied to the quantification of glucose with a linear range covering from 1.0 × 10⁻⁷ to 5 × 10⁻³ M and a low detection limit of 3 × 10⁻⁸ M. Furthermore, the experiment results also showed that the biosensor exhibited good reproducibility and long-term stability, as well as high selectivity with no interference from other oxidable species.     

Sulfite oxidase biosensors based on tetrathiafulvalene modified screen-printed carbon electrodes for sulfite determination in wine

Screen-printed carbon electrodes have been modified with tetrathiafulvalene and sulfite oxidase enzyme for the sensitive and selective detection of sulfite. Amperometric experimental conditions were optimized taking into account the importance of quantifying sulfite in wine samples and the inherent complexity of these samples, particularly red wine. The biosensor responds to sulfite giving a cathodic current (at +200 mV vs screen-printed Ag/AgCl electrode and pH 6) in a wide concentration range, with a capability of detection of 6 μM (α = β = 0.05) at 60 °C. The method has been applied to the determination of sulfite in white and red samples, with averages recoveries of 101.5% to 101.8%, respectively.