Langmuir-Blodgett films from polyaniline/ruthenium complexes as modified electrodes for detection of dopamine

Langmuir-Blodgett (LB) films from mixtures of polyaniline (PANI) and the ruthenium complex mer-[RuCl₃(dppb)(py)] (dppb=PPh₂(CH₂)₄PPh₂; py=pyridine) (Rupy) were used to modify electrodes and to detect dopamine (DA). The electrochemical response has been used as the principle of detection in order to exploit the molecular-level interaction between PANI and Rupy in the LB films. Cyclic voltammograms were performed in a potential range where the Rupy complex is not electroactive and the response is dominated by the interconversion between the oxidation states leucoemeraldine and emeraldine of PANI. In the presence of DA a further redox pair appears at approximately 230 and 0 mV, associated with oxidation/reduction of DA to dopaminequinone. The current increased linearly in the range between 4.0×10⁻⁵ and 1.2×10⁻³ mol/l. The detection limit for DA concentrations for the 21-layer LB film from PANI/Rupy was 4.0×10⁻⁵ mol/l, which is sufficient to detect DA in a pharmaceutical product. The modified electrode based on PANI/Rupy LB films is selective to DA, particularly because the oxidation potential for DA is lowered, in comparison to a bare indium-tin-oxide electrode. The presence of ascorbic acid, which is an important interferent for DA, could be detected when its concentration was three times that of DA.     

铂粒子修饰的聚苯胺/醋酸纤维素复合膜电极对甲醛的催化氧化

采用循环伏安法在酸性溶液中成功的制备出聚苯胺(PANI)/醋酸纤维素(CA)复合膜,原子力显微镜显示:复合膜具有不对称的微孔结构,正面是不规则微孔结构的聚苯胺层,反面是海绵状的醋酸纤维素层.用电沉积法将铂沉积到PANI/CA复合膜上,研究发现Pt修饰的PANI/CA复合膜电极对甲醛有较高的催化活性和稳定性.     

Simple and convenient preparation of Au-Pt core-shell nanoparticles on surface via a seed growth method

Au-Pt core-shell nanoparticles were prepared on glass surface by a seed growth method. Gold nanoparticles were used as seeds and ascorbic acid-H₂PtCl₆ solutions as growth solutions to deposit Pt shell on the surface of gold nanoparticles. These core-shell nanoparticles and their growth process were examined by UV-Vis spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy and field-emission environmental scanning electron microscopy and the results indicated that the deposition speed was fast and nanoparticles with obvious core-shell structure could be obtained after 2 min. Moreover, this seed growth method for preparation of the core-shell nanoparticles is simple and convenient compared with other seed growth methods with NH₄OH as a mild reductant. In addition, electrochemical experiments indicated that these Au-Pt core-shell nanoparticles had similar electrochemical properties to those of the bulk Pt electrode.     

Synthesis of hollow polyaniline nanoparticles with reactive template

γ-Fe₂O₃ nanoparticles were used as the reactive templates for the fabrication of the hollow polyaniline nanoparticles via the chemical oxidative polymerization of aniline in the presence of hydrochloric acid. The particle size of the doped hollow polyaniline nanoparticles in the emeraldine form was determined by the reactive template. It was found that the reacting temperature played an important role in the formation of the hollow nanoparticles because of the low redox potential of Fe(III) ion. However, the kind of the protonic acids used had no influence on the fabrication of the hollow nanostructure. The formation mechanism of the hollow polyaniline nanoparticles was also proposed.     

Synthesis and enhanced electrochemical properties of pod-shaped gold/silica nanoparticles

Pod-shaped gold/silica nanoparticles (PGSNPs) were prepared using perfluorooctanoic acid (PFOA) and cetyltrimethylammonium bromide (CTAB) as cotemplates. The PGSNPs were utilized to explore a novel biosensor through coupling myoglobin (Mb) with chitosan (Chi). Compared with Mb-Chi-PSNPs (pod-shaped silica nanoparticles)/GC modified electrode, Mb-Chi-PGSNPs/GC electrode exhibited a pair of much stronger redox peaks at − 0.28 V (vs. Ag/AgCl). Moreover, facilitated direct electron transfer of the metalloenzymes with smaller peak-to-peak separation (ΔEp) of about 46 mV was acquired on the PGSNPs-based enzyme electrode. The PGSNPs-based biosensor demonstrated significant electrocatalytic activity for the reduction of hydrogen peroxide with a wide linear range (1-540 µM) and high sensitivity (661 mA cm^− 2 M^− 1). Together, the Mb-Chi-PGSNPs film is one of ideal candidate materials for direct electrochemistry of redox proteins, and may find potential applications in biomedical, food, and environmental analysis and detection.     

Ionic interactions of microspheres. Reversible coating of Prussian blue nanoparticles on the submicrospheres of platinum(II) complexes

The submicrospherical morphology is conveniently formed by a reaction of platinum(II) species in water with new pyridyl ligand in acetone, and followed by evaporation of acetone. The amphiphilic properties of ionic platinum(II) complex containing a long aliphatic chain allow to form a monodisperse submicrosphere morphology without any template or additive. A reversible coating of Prussian blue nanoparticles on the submicrospheres has been carried out. Furthermore, the submicrospheres form a unique monolayer on a micro cotton thread or a glass fiber. The ionic and amphiphilic properties of the surface appear to be primarily associated with the easy formation of coating and arrays of monolayer.     

Surfactant-associated electrochemical properties of ferrocene adsorbed on a glassy carbon electrode modified with multi-walled carbon nanotubes

The electrochemical properties of ferrocene (Fc) on a glassy carbon (GC) electrode modified by multi-walled carbon nanotubes (MWNTs) in the presence and absence of surfactants have been investigated by progressively voltammetric sweeping. Dihexadecyl phosphate (DHP) and hexadecyl trismethyl ammonium chloride (HTAC) are found to impact the redox reactions of Fc adsorbed on MWNT surfaces. An excess amount of DHP dispatches Fc from MWNTs surfaces, leading to weakly adsorbed configuration of Fc. The formal potential of the adsorbed Fc in the presence of DHP shifts to a lower potential. Cationic surfactant HTAC on MWNT surfaces depresses the redox reactions corresponding to the weakly adsorbed configuration of Fc. It becomes evident that the configuration and hence redox reactions of Fc depend strongly on the presence and concentrations of surfactants on the electrode surfaces and in the buffer solutions.     

Precursor solvent influence on preparation and electrochemical properties of platinum nanoparticles electrodes

The crystalline sizes and loading efficiencies of metallic nanoparticles for fuel cell catalysts have been measured by changing solvent species containing precursors. By changing the solvent species containing carbon particles and metal salt, the microstructure and the according electrochemical property of catalysts could be controlled. Four kinds of solvent were investigated in this study. Pt catalysts that were deposited on carbon blacks supports by using an ethylene glycol solution showed the highest deposition efficiency, 85% and smallest crystalline size, 2.85 nm of particles. From the experimental result, it was concluded that the electrochemical performance of catalysts was dependent on the crystalline size and deposition efficiency of metal particles, by changing solvent species.     

Phase separation and surface morphology of spin-coated films of polyetherimide/polycaprolactone immiscible polymer blends

The surface morphology in thin films of immiscible polyetherimide and polycaprolactone blends was studied using scanning electron and atomic force microscopy. The thin films were obtained by spin-coating from dichloromethane solution. A self-assembled periodic pattern of phase separated domains was observed, which was induced by capillary effects along with the solution radial flow and the unsteady air flow field above the film during the initial stages of spin-coating. A secondary phase separation was observed during the solvent evaporation stage of spin-coating. The differences in surface topographies of the two distinct phases are attributed to different solvent evaporation rates within each phase. In addition, a great variety of domain structures and surface morphologies were observed as a function of polymer blend composition.     

Photo- and electroluminescence properties of fluorene-based copolymers containing electron- or hole-transporting unit

We report the photophysical and electroluminescence (EL) properties of two fluorene-based copolymers, poly{[9,9-bis(2-ethylhexyl)fluorene-2,7-diyl]-alt-[6,6′- bis(3-phenylquinoxaline)-2,2′-diyl]} (Qx-PF) and poly{[9,9-bis(2- ethylhexyl)fluorene-2,7-diyl]-alt-[N,N′-diphenyl-N,N′-bis(4-phenyl)-1,1′-biphenyl-4,4′-diamine]} (TPD-PF). The two copolymers in thin films show blue emission approximately 429-452 nm with relatively narrow bandwidth upon photoexcitation. Electroluminescence has been demonstrated using TPD-PF as the active polymer in the light-emitting electrochemical cell (LEC) with a turn-on voltage at 2.8 V and an EL efficiency of 0.002 cd/A. Due to the improved electron-transporting property, the Qx-PF-based LEC achieves the EL efficiency of 0.07 cd/A, 35 times higher than that of the TPD-PF-based device. Compared to the photoluminescence spectra, EL spectra show enhanced excimer emission, which is primarily related to self-heating of the devices during operation. The main process involved in the decrease of the light intensity during device operation is the electrochemical degradation of the polymer blend.     

Synthesis and electrical properties of polymer composites with polyaniline nanoparticles

Nano-sized polyaniline (PANI) particles dispersed in aqueous solution were prepared using both poly(vinyl alcohol) (PVA) and poly(styrene sulfonic acid) (PSSA) as polymeric stabilizers. Size of the spherical PANI particle synthesized using PVA with a HCl dopant (PANI-HCl/PVA) was about 150 nm in diameter, and that with PSSA (PANI-PSSA) was about 50 nm, with a uniform size distribution. Doping level of the PANI-PSSA measured by UV–visible spectrometer was higher than that of PANI-HCl/PVA. The PVA based composite films using both PANI-HCl (PANI-HCl/PVA) and PANI-PSSA (PANI-PSSA/PVA) were prepared by a casting method for different PANI content and their electrical conductivities were measured. A percolation threshold of PANI concentration for conductivity of composite was found only around 10 wt.% of PANI for the PANI-PSSA/PVA, and furthermore, the PANI-PSSA/PVA became more conductive above the threshold point than PANI-HCl/PVA.     

磺基水杨酸掺杂导电聚苯胺纳米材料的制备与性能研究

采用化学氧化法以苯胺为单体,过硫酸铵为氧化剂,磺基水杨酸为掺杂酸合成聚苯胺纳米棒导电材料。考察了单体/掺杂酸摩尔比对聚苯胺形貌与电性能的影响,采用傅里叶红外光谱,XRD粉末衍射表征聚苯胺结构;电化学工作站、四探针研究表明聚苯胺的导电性随掺杂酸/单体摩尔比的增大而增大,单体/掺杂酸摩尔比为2时电导率为1.43S/cm;SEM、TEM表明聚苯胺纳米棒表面粗糙,直径约为100～200nm,长度约为400～700nm,表面附着了1层10～30nm厚的颗粒;并提出了纳米棒可能的形成机理。     

Highly selective and sensitive electrochemical detection of dopamine using a nafion coated hybrid macroporous gold modified electrode with platinum nanoparticles

A coral-like macroporous Au electrode with electroplated Pt nanoparticles (hybrid macroporous Au-/nPts) coated with Nafion has been fabricated for the first time and used for highly selective and sensitive determination of dopamine (DA). The physically characterized results indicated that the electroplated Pt nanoparticles were dispersed uniformly on the macroporous Au electrode. The porosity and window pore size of the fabricated macroporous Au electrode were 50% and 100-300 nm, respectively. Also the electroplated Pt nanoparticles size was approximately 10-20 nm. The cyclic voltammograms results showed that the hybrid macroporous Au-/nPts exhibited a much larger surface activation area, a roughness factor (RF) of 2024.7, much higher than that of the macroporous Au electrode, which is 46.07. The electrochemical experimental results showed that the hybrid macroporous Au-/nPts coated with Nafion exhibited a dramatic electrocatalytic effect on the oxidation of DA. At 0.1 V, it responded linearly to DA concentrations ranging from 20 μ M to 160 μ M with a detection sensitivity of 90.9 μA mM (-1) cm (-2). Furthermore, it showed wide detection ranging from 20 nM to 900 μ M. At the same time, the interference of ascorbic acid (AA) was effectively avoided because of the Nafion film coated on the surface of the hybrid electrode.     

Highly dense and uniformly dispersed platinum nanoparticles on poly(acrylic acid) modified multi-walled carbon nanotubes for methanol oxidation

Poly(acrylic acid) modified multi-walled carbon nanotubes (PAA-MWNTs) were synthesized through in situ radical polymerization in acetone and the PAA-MWNTs were used as supporting material for platinum nanoparticles. Platinum nanoparticles were deposited on the surface of PAA-MWNTs with high loading and high dispersion through ethylene glycol reduction. The size of Pt nanoparticles on PAA-MWNTs can be tuned by the water content in the reaction system and the loading amount can be adjusted by the mass ratio of H₂PtCl₆ to PAA-MWNTs. The electrocatalytic properties of the Pt/PAA-MWNTs catalyst were evaluated by methanol oxidation. The results of cyclic voltammetry show that the Pt/PAA-MWNTs composite possesses high electrocatalytic activity, good long-term stability and storage property, which can be attributed to the small particle size and high dispersion of Pt nanoparticles as well as the nature of MWNTs.     

Interfacial synthesis of platinum loaded polyaniline nanowires in poly(styrene sulfonic acid)

Polyaniline-poly(styrene sulfonic acid)-platinum (PANI-PSS-Pt) composite is prepared through an interfacial polymerization route. The composite is obtained by incorporating Pt nanoparticles into conductive PANI matrix by the reduction of Pt⁴⁺ ions to Pt nanoparticles during the oxidative polymerization of aniline in PSS as medium. The interfacial synthesis offers the microenvironment for the growth of PANI nanostructures with simultaneous incorporation of Pt nanoparticles to result PANI-PSS-Pt nanocomposite. PANI-PSS-Pt nanocomposite is characterized by UV-Vis absorption spectroscopy, FTIR spectroscopy, scanning microelectronic microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS).     

Unique properties of polyaniline in the presence of applied magnetic field and ferric chloride

Fe-contained polyaniline (abbreviated as PANI–Fe) was prepared by chemical oxidation of aniline with ammonium peroxydisulfate oxidant in 0.5 mol dm⁻³ HCl and an adequate content of FeCl₃·6H₂O solution in the presence of an applied magnetic field at room temperature. The X-ray photoelectron spectroscopy (XPS) and UV–vis and FTIR spectra suggest that there is an interaction between FeCl₃ and PANI chains, but PANI–Fe backbone is essentially identical with that of parent polyaniline. The electron paramagnetic resonance (EPR) spectrum shows that there were unpaired electrons in PANI–Fe synthesized in the presence of an applied magnetic field, the spin density and the conductivity of which are 7.308 × 10²⁰ spins g⁻¹ and 0.891 S cm⁻¹, respectively. The plot of magnetization (M) vs. the applied magnetic field (H) displays that the PANI–Fe possesses soft ferromagnetic behavior at room temperature. The results of cyclic voltammogram show that the PANI–Fe film is of excellent electrochemical activity.     

Thermal stability of composites containing HCl-doped polyaniline and Fe nanoparticles

HCl-doped polyaniline (HCl-PANI) powder was mechanically mixed with Fe nanoparticles to obtain the HCl-PANI–Fe composite. The composite pellets containing 30 and 50 wt% Fe nanoparticles were heated in air at 50, 100, 150 and 200 °C for times up to 60 min. The heat treatment degrades the crystallinity of the HCl-PANI and promotes the oxidation of the Fe nanoparticles. After heat-treating, the aromatic structure of PANI is retained in the HCl-PANI and HCl-PANI–Fe pellets. However, the heat treatment causes the dopant dedoping from the polymer backbones. The HCl-PANI–Fe composite pellets heated are in a higher reduction state compared with the unheated ones. Thermogravimetric analysis reveals that a weight loss decreases with increasing the Fe nanoparticle content at the same heating temperature. The weight loss increases rapidly within the first 5-min isothermal time at 200 °C. The conductivity decreases with increasing the heat-treating temperature. A rapid decrease in the conductivity happens within the first 20-min heat-treating time for the HCl-PANI–30 wt% Fe composite and within the first 10-min heat-treating time for the HCl-PANI–50 wt% Fe composite at 200 °C. The composites exhibit a narrow hysteresis curve typical for superparamagnetic nanoparticles and the magnetization behavior is independent of the heat-treating conditions.     

Fabrication and characterization of platinum black and mesoporous platinum electrodes for in-vivo and continuously monitoring electrochemical sensor applications

Most electrochemical biosensors are disposable due to enzymes that are living creatures. Thus, these are limited to use in in-vivo and continuously monitoring biosensor system applications. The mesoporous (pores with a size of 2-50 nm) platinum (Pt) structure formed on a rod-shaped Pt microelectrode was reported for developments glucose sensors without any enzymes. In this paper, plane Pt electrode (non-treated), Pt black electrode, and mesoporous Pt electrode are fabricated and characterized on a silicon substrate in order to check their usability as enzymeless sensing electrodes for in-vivo and continuously monitoring electrochemical biosensors integrated with silicon CMOS read-out circuitry. The Pt black electrode with rough surface was fabricated by using an electrodeposition technique with hexachloroplatinic acid hydrate (HCPA) solutions. The proposed mesoporous Pt electrode with approximately 3 nm in pore diameter was fabricated by using an electrodeposition technique with nonionic surfactant octaethylene glycol monohexadecyl ether (C₁₆EO₈) and HCPA. The measured current responses at 40 mM glucose solution of the fabricated plane Pt, Pt black, and mesoporous Pt electrodes are approximately 12.4 nA/mm², 2.1 μA/mm², and 2.8 μA/mm², respectively. These data indicate that the mesoporous Pt electrode is much more sensitive than the other Pt electrodes and has strong potential for enzymeless electrochemical sensor applications.     

Investigations of the properties of the manganese dioxide suspensions in the presence of guar gum and carboxymethylcellulose

Properties of manganese dioxide suspensions in the presence of two polysaccharides: non-ionic guar gum (GG) and anionic carboxymethylcellulose (CMC) were investigated using NaCl as a background electrolyte. The colloidal stability of MnO₂ suspensions in the presence and absence of these two polymers was measured. It was found that both polymers improve stability of measured suspensions. This fact results from steric stabilization (low polymer concentrations) and depletion stabilization (high polymer concentrations) for MnO₂ particles covered with macromolecules. Next the kinetics of the adsorption of these two polymers on MnO₂ as well as the heats of GG and CMC adsorption processes were measured. The obtained data proved that CMC is adsorbed more effectively on the manganese dioxide surface than guar gum. To obtain more information about the changes of adsorption of these polymers on MnO₂ some factors influencing this process (pH, ionic strength of the background electrolyte) were investigated. The data obtained from the surface charge density and the zeta potential measurements allowed the analysis of the structure of the electric double layer created by polymers on the solid surface.     

Electrochemical determination of cadmium(II) at platinum electrode modified with kaolin by square wave voltammetry

In this work, determination of cadmium(II) using square wave voltammetry (SWV) was described. The method is based on accumulation of these metal ions on kaolin platinum electrode (K/Pt). The K/Pt performance was optimized with respect to the surface modification and operating conditions. The optimized conditions were obtained in pH of 5.0 and accumulation time of 25 min. Under the optimal conditions, the relationship between the peak current versus concentration was linear over the range of 9 × 10⁻⁸ to 8.3 × 10⁻⁶ mol L⁻¹. The detection limit (DL, 3σ) was 5.4 × 10⁻⁹ mol L⁻¹. The analytical methodology was successfully applied to monitor the Cd(II) content in natural water. Interferences were also evaluated.