New method for preparation of polyoxometalate-capped gold nanoparticles, and their assembly on an indium-doped tin oxide electrode

Functionalized gold nanoparticles capped with polyoxometalates were prepared by a simple photoreduction technique where phosphododecamolybdates serve as reducing reagents, photocatalysts, and as stabilizers. TEM images of the resulting gold nanoparticles show the particles to have a relative narrow size distribution. Monolayer and multilayer structures of the negatively charged capped gold nanoparticles were deposited on a poly(vinyl pyridine)-derivatized indium-doped tin oxide (ITO) electrode via the layer-by-layer technique. The surface plasmon resonance band of the gold nanoparticles displays a blue shift on the surface of the ITO electrode. This is due to the substrate-induced charge redistribution in the gold nanoparticles and a change in the electromagnetic coupling between the assembled nanoparticles. The modified electrode exhibits the characteristic electrochemical behavior of surface-confined phosphododecamolybdate and excellent electrocatalytic activity. The catalysis of the modified electrode towards the model compound iodate was systematically studied. The heterogeneous catalytic rate constant for the electrochemical reduction of iodate was determined by chronoamperometry to be ca. 1.34?×?10⁵ mol^?1·L·s^?1. The amperometric method gave a linear range from 2.5?×?10^?6 to 1.5?×?10^?3 M and a detection limit of 1.0?×?10^?6 M. We believe that the functionalized gold nanoparticles prepared by this photoreduction technique are advantageous in terms of fabrication of sensitive and stable redox electrodes.

Poly(ethylene oxide)–poly(ethylene imine) block copolymers as templates and catalysts for the in situ formation of monodisperse silica nanospheres

Block copolymers based on poly(ethylene oxide) (PEO) and poly(ethylene imine) (PEI) are efficient catalysts/templates for the formation of uniform silica nanoparticles. Addition of tetraethylorthosilicate to a solution of PEO–PEI or PEI–PEO–PEI block copolymers results in the formation of silica particles with a diameter of ca. 30 nm and narrow size distribution. The particles precipitated with the diblock copolymers can be redispersed in water after isolation as individual nanoparticles. Evidently, block copolymers based on PEO and PEI serve as excellent templates for the biomimetic and “soft” synthesis of silica nanoparticles.

Preparation of PMMA/acid-modified chitosan core-shell nanoparticles and their potential as gene carriers

The core-shell nanoparticles consisting of poly(methyl methacrylate) (PMMA) cores surrounded by various acid-modified chitosan shells were synthesized using a surfactant-free emulsion copolymerization, induced by a tert-butylhydroperoxide (TBHP) solution. Methyl methacrylate (MMA) was grafted onto four acid-modified chitosans (hydrochloric, lactic, aspartic, and glutamic acids) with MMA conversions up to 64%. The prepared nanoparticles had diameter ranging from 100 to 300 nm characterized by atomic force microscopy and displayed highly positive surface charges up to +77 mV. Transmission electron microscopic images clearly revealed well-defined core-shell morphology of the nanoparticles where PMMA cores were coated with acid-modified chitosan shells. The effect of acid-modified chitosans on particle size, intensity of surface charge, morphology, and thermal stability were determined systematically. The plasmid DNA/nanoparticles complexes were investigated with ζ-potential measurement. The results suggested that these nanoparticles can effectively complex with plasmid DNAs via electrostatic interaction and could be used as gene carriers.

Activated carbon functionalized with 1-amino-2-naphthol-4-sulfonate as a selective solid-phase sorbent for the extraction of gold(III)

We describe the synthesis of spherical poly(vinyl butyral) (PVB) nanobeads by controlled precipitation via addition of non-solvent. Effects of various reaction parameters on nanoparticle size were investigated by dynamic light scattering and electron microscopy. The ability to incorporate dopant molecules was studied using a fluorescent perylene derivative as a model additive, and the dye-doped nanoparticles were investigated by confocal microscopy. In an optimized experimental protocol, PVB nanoparticles were obtained that were efficiently taken up by human cancer cells devoid of coating. The novel nanospheres are economic, easy to prepare and capable of incorporating additives. Lacking cytotoxicity in vitro, PVB nanobeads are attractive with respect to various potential applications such as optical imaging and particle tracking, diagnostics, and drug delivery.

Ultra-sensitive electrochemical DNA biosensor based on signal amplification using gold nanoparticles modified with molybdenum disulfide,graphene and horseradish peroxidase

We have developed an ultra-sensitive electrochemical DNA biosensor by assembling probe ssDNA on a glassy carbon electrode modified with a composite made from molybdenum disulfide, graphene, chitosan and gold nanoparticles. A thiol-tagged DNA strand coupled to horseradish peroxidase conjugated to AuNP served as a tracer. The nanocomposite on the surface acts as relatively good electrical conductor for accelerating the electron transfer, while the enzyme tagged gold nanoparticles provide signal amplification. Hybridization with the target DNA was studied by measuring the electrochemical signal response of horseradish peroxidase using differential pulse voltammetry. The calibration plot is linear in the 5.0?×?10^?14 and 5.0?×?10^?9 M concentration range, and the limit of detection is 2.2?×?10^?15 M. The biosensor displays high selectivity and can differentiate between single-base mismatched and three-base mismatched sequences of DNA. The approach is deemed to provide a sensitive and reliable tool for highly specific detection of DNA.

Studies on the electrochemistry of rutin and its interaction with bovine serum albumin using a glassy carbon electrode modified with carbon-coated nickel nanoparticles

We report on a glassy carbon electrode modified with carbon-coated nickel nanoparticles (C-Ni/GCE) that can be used to study the electrochemical properties of rutin and its interaction with bovine serum albumin (BSA) via cyclic voltammetry and differential pulse voltammetry. The effects of pH value, accumulation potential, accumulation time and reaction time were optimized. A pair of reversible peaks is found in the potential range of 0 to around 0.6 V at pH?5.0. Two linear response ranges (with different slopes) are found, one in the 2 to 210 nM concentration range, the other between 0.21 and 1.72 μM. The detection limit is as low as 0.6 nM. On addition of BSA to the rutin solution, a decrease of the current is observed that is proportional to the concentration of BSA. The binding constant and stoichiometric ratio were calculated.

A composite made from palladium nanoparticles and carbon nanofibers for superior electrocatalytic oxidation of formic acid

We report on a novel type of nanocomposite for use in the electrooxidation of formic acid in fuel cells. The material is composed of palladium nanoparticles (Pd-NPs) and carbon nanofibers (CNFs) and was prepared by electrospinning of the precursors Pd(acac)₂ and polyacrylonitrile, respectively, followed by thermal treatment to generate in-situ Pd-NPs that are well dispersed within the CNF framework. The nanocomposite was characterized by TEM, high-resolution TEM, SEM, XRD, Raman spectroscopy, and XPS. The size of the Pd-NPs ranges from 12 to 82 nm, depending on the temperature for carbonization (700–1,000 °C). The length and width of the CNF is in the order of tens of micrometers and 300 to 500 nm, respectively. TEM and XPS studies indicate that the Pd-NPs are firmly embedded in the CNF, resulting in a good electrochemical stability of the composite. The electrocatalytic properties of the composite with respect to the oxidation of formic acid were studied by cyclic voltammetry and chronoamperometry. They showed a distinctly improved electrocatalytic activity and stability compared to a commercial Pd-on-carbon catalyst. The Pd/CNF composite carbonized at 900 °C was found to display the best performance.

Modelling the size and polydispersity of magnetic hybrid nanoparticles for luminescent sensing of oxygen

We report on a strategy to model both the size (d) and the polydispersity (PdI) of magnetic oxygen-sensitive nanoparticles with a typical size of 200 nm in order to increase the surface area. The strategy is based on experimental design and Response Surface Methodology. Nanoparticles were prepared by miniemulsion solvent evaporation of solutions of poly(styrene-co-maleic anhydride). Features of this strategy include (1) a quick selection of the most important variables that govern d and PdI; (2) a better understanding of the parameters that affect the performance of the polymer; and (3) optimized conditions for the synthesis of nanoparticles of targeted d and PdI. The results were used to produce nanoparticles in sizes that range from 100 to 300 nm and with small polydispersity. The addition of a platinum porphyrin complex that acts as a luminescent probe for oxygen and of magnetite (Fe₃O₄) to the polymeric particles, did not affect d and PdI, thus demonstrating that this strategy simplifies their synthesis. The resulting luminescent and magnetic sensor nanoparticles respond to dissolved oxygen with sensitivity (Stern-Volmer constant) of around 35 bar^?1.

Prussian blue-doped nanogold microspheres for enzyme-free electrocatalytic immunoassay of p53 protein

We report on a new enzyme-free electrochemical immunoassay for the sensitive detection of the p53 protein (p53; a model analyte) by using a screen-printed carbon electrode modified with monoclonal mouse anti-human p53 antibody tagged with gold nanoparticles. First, nanogold microspheres doped with Prussian Blue were synthesized by a reverse micelle method. The resulting microspheres were used to label polyclonal anti-p53 antibody which then was applied in a sandwich immunoassay in pH 6.5 buffer solution using the Prussian Blue in the particles as the redox-active reporter. The electrochemical signal of the immunosensor is shown to increase with the concentration of the analyte (p53 protein) in the range from 0.5 to 80 U mL^?1, with a detection limit of 0.1 U mL^?1. No non-specific adsorption was observed. Coefficients of variation for intra-assay and inter-assay were below 8.5 % and 11.5 %, respectively. In addition, the method was applied to the analysis of 15 human serum samples, and a good relationship was found between the new immunoassay and the referenced electro-chemiluminescence method.

Facile synthesis of a porous network-like silver film for electrocatalytic detection of nitrate

We have developed a method for in-situ construction of a porous network-like silver film on the surface of a glassy carbon electrode (GCE). It is based on a galvanic replacement reaction where a layer of copper nanoparticles is first electrodeposited as a sacrificial template. The silver film formed possesses a porous network-like structure and consists of an assembly of numerous nanoparticles with an average size of 200 nm. The electrode displays excellent electrocatalytic activity, good stability, and fast response (within 2 s) toward the reduction of nitrate at a working potential of ?0.9 V. The catalytic currents linearly increase with the nitrate concentrations in the range of 0.08–6.52 mM, with a detection limit of 3.5 μM (S/N?=?3) and a repeatability of 3.4 % (n?=?5).

Electrochemistry and voltammetric determination of L-tryptophan and L-tyrosine using a glassy carbon electrode modified with a Nafion/TiO2-graphene composite film

We describe a glassy carbon electrode (GCE) modified with a film composed of Nafion and TiO₂-graphene (TiO₂-GR) nanocomposite, and its voltammetric response to the amino acids L-tryptophane (Trp) and L-tyrosine (Tyr). The incorporation of TiO₂ nanoparticles with graphene significantly improves the electrocatalytic activity and voltammetric response compared to electrodes modified with Nafion/graphene only. The Nafion/TiO₂-GR modified electrode was used to determine Trp and Tyr with detection limits of 0.7 and 2.3 μM, and a sensitivity of 75.9 and 22.8 μA mM^?1 for Trp and Tyr, respectively.

A lipase-based electrochemical biosensor for target DNA

A lipase-based electrochemical biosensor has been fabricated for the quantitative determination of target DNA. It is based on a stem-loop nucleic acid probe labeled with ferrocene containing a butanoate ester that is hydrolyzed by lipase. The other end of the probe DNA is linked, via carboxy groups, to magnetic nanoparticles. The binding of target DNA transforms the hairpin structure of the probe DNA and causes the exposure of ester bonds. This results in the release of electro-active ferrocene after hydrolysis of the ester bonds, and in an observable electrochemical response. The quantity of target DNA in the concentration range between 1?×?10^?12 mol·L^?1 and 1?×?10^?8 mol·L^?1 can be determined by measuring the electrochemical current. The method can detect target DNA with rapid response (30 min) and low interference.

Sputtering deposition of Pt nanoparticles on vertically aligned multiwalled carbon nanotubes for sensing L-cysteine

A highly sensitive electrochemical sensor for determination of L-cysteine (CySH) is presented. It is based on vertically aligned multiwalled carbon nanotubes modified with Pt nanoparticles by magnetron sputtering deposition. The morphology of the nanocomposite was characterized by scanning electron microscopy, transmission electron microscopy and energy-dispersive. The electrochemistry of CySH was investigated by cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The mechanism for the electrochemical reaction of CySH at the modified electrode at different pH values is discussed. The electrode exhibits a higher electrocatalytic activity towards the oxidation of CySH than comparable other electrodes. It displays a linear dependence (R ²?=?0.9980) on the concentration of CySH in the range between 1 and 500 μM and at an applied potential of +0.45 V, a remarkably low detection limit of 0.5 μM (S/N?=?3), and an outstandingly high sensitivity of 1.42?×?10³ μA?mM^?1?cm^?2, which is the highest value ever reported. The electrode also is highly inert towards other amino acids, creatinine and urea. The sensor was applied to the determination of CySH in urine with satisfactory recovery, thus demonstrating its potential for practical applications.

Electrochemical sensing of catechol using a glassy carbon electrode modified with a composite made from silver nanoparticles, polydopamine, and graphene

We report on the modification of a glassy carbon electrode with a composite consisting of silver nanoparticles (AgNPs), polydopamine, and graphene to give an electrochemical sensor for catechol. The composite was characterized by transmission electron microscopy, and the electrochemical behavior of catechol at the modified electrode was studied by cyclic voltammetry. The electrochemical response is greatly enhanced and thought to result from a combination of beneficial effects including the good conductivity and large surface area of the AgNPs, the high conductivity of graphene, the synergistic effects of the composite, and the increased quantity of catechol that is adsorbed on the surface of the electrode. Differential pulse voltammetric responses are proportional to the concentration of catechol between 0.5 and 240?μM levels of catechol, and the detection limit is 0.1?μM (S/N?=?3). The performance of the sensor was evaluated with catechol-spiked water samples, and recoveries range from 96.5 % to 103.1 %. The results indicated that the composite presented here is a promising substrate for use in electrochemical sensing.

Particle Production in Reflection and Transmission Mode Laser Ablation: Implications for Laserspray Ionization

Particles were ablated from laser desorption and inlet ionization matrix thin films with a UV laser in reflection and transmission geometries. Particle size distributions were measured with a combined scanning mobility particle sizer (SMPS) and aerodynamic particle sizer (APS) system that measured particles in the size range from 10 nm to 20 μm. The matrixes investigated were 2,5-dihydroxybenzoic acid (DHB), α-cyano-4-hydroxycinnamic acid (CHCA), sinapic acid (SA), 2,5-dihydroxy-acetophenone (DHAP), and 2-nitrophloroglucinol (NPG). Nanoparticles with average diameters between 20 and 120 nm were observed in both transmission and reflection geometry. The particle mass distribution was significantly different in reflection and transmission geometry. In reflection geometry, approximately equal mass was distributed between particles in the 20 to 450 nm range of diameters and particles in the 450 nm to 1.5 μm diameter range. In transmission mode, the particle mass distribution was dominated by large particles in the 2 to 20 μm diameter range. Ablation of inlet ionization matrices DHAP and NPG produced particles that were 3 to 4 times smaller compared with the other matrices. The results are consistent with ion formation by nanoparticle melting and breakup or melting and breakup of the large particles through contact with heated inlet surfaces.

Dopamine sensor based on a glassy carbon electrode modified with a reduced graphene oxide and palladium nanoparticles composite

We report on a sensitive electrochemical sensor for dopamine (DA) based on a glassy carbon electrode that was modified with a nanocomposite containing electrochemically reduced graphene oxide (RGO) and palladium nanoparticles (Pd-NPs). The composite was characterized by scanning electron microscopy, energy dispersive spectroscopy, and electrochemical impendence spectroscopy. The electrode can oxidize DA at lower potential (234 mV vs Ag/AgCl) than electrodes modified with RGO or Pd-NPs only. The response of the sensor to DA is linear in the 1–150 μM concentration range, and the detection limit is 0.233 μM. The sensor was applied to the determination of DA in commercial DA injection solutions.

Sensitive electrochemical sensor for hydrogen peroxide using Fe3O4 magnetic nanoparticles as a mimic for peroxidase

A sensor for hydrogen peroxide is described that is based on an indium tin oxide electrode modified with Fe₃O₄ magnetic nanoparticles which act as a mimic for the enzyme peroxidase and greatly improve the analytical performance of the sensor. The amperometric current is linearly related to the concentration of H₂O₂ in the range from 0.2 mM to 2 mM, the regression equation is y?=?-0.5–1.82x, the correlation coefficient is 0.998 (n?=?3), and the detection limit is 0.01 mM (S/N?=?3). The sensor exhibits favorable selectivity and excellent stability.

Iodide-induced adsorption of lead(II) ion on a glassy carbon electrode modified with ferroferric oxide nanoparticles

Spherical Fe₃O₄ nanoparticles (NPs) were prepared by hydrothermal synthesis and characterized by scanning electron microscopy and X-ray diffraction. A glassy carbon electrode was modified with such NPs to result in a sensor for Pb(II) that is based on the strong inducing adsorption ability of iodide. The electrode gives a pair of well-defined redox peaks for Pb(II) in pH 5.0 buffer containing 10 mM concentrations of potassium iodide, with anodic and cathodic peak potentials at ?487 mV and ?622 mV (vs. Ag/AgCl), respectively. The amperometric response to Pb(II) is linear in the range from 0.10 to 44 nM, and the detection limit is 40 pM at an SNR of 3. The sensor exhibits high selectivity and reproducibility.

Electrochemical synthesis of a graphene sheet and gold nanoparticle-based nanocomposite, and its application to amperometric sensing of dopamine

We describe a simple, green and controllable approach for electrochemical synthesis of a nanocomposite made up from electrochemically reduced graphene oxide (ERGO) and gold nanoparticles. This material possesses the specific features of both gold nanoparticles and graphene. Its morphology was characterized by scanning electron microscopy which reveals a homogeneous distribution of gold nanoparticles on the graphene sheets. Cyclic voltammetry was used to evaluate the electrochemical properties of this nanocomposite towards dopamine by modification of it on surface of glassy carbon electrode (GCE). Compared to the bare GCE, the electrode modified with gold nanoparticles, and the electrode modified with ERGO, the one modified with the nanocomposite displays better electrocatalytic activity. Its oxidation peak current is linearly proportional to the concentration of dopamine (DA) in the range from 0.1 to 10?μM, with a detection limit of 0.04?μM (at S/N?=?3). The modified electrode also displays good storage stability, reproducibility, and selectivity.

Protein-directed in situ synthesis of platinum nanoparticles with superior peroxidase-like activity, and their use for photometric determination of hydrogen peroxide

Platinum nanoparticles (Pt-NPs) with sizes in the range from 10 to 30 nm were synthesized using protein-directed one-pot reduction. The model globular protein bovine serum albumin (BSA) was exploited as the template, and the resulting BSA/Pt-NPs were studied by transmission electron microscopy, energy dispersive X-ray spectroscopy, and resonance Rayleigh scattering spectroscopy. The modified nanoparticles display a peroxidase-like activity that was exploited in a rapid method for the colorimetric determination of hydrogen peroxide which can be detected in the 50 μM to 3 mM concentration range. The limit of detection is 7.9 μM, and the lowest concentration that can be visually detected is 200 μM.