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.     

硫化镉和硫化银与多壁碳纳米管复合材料合成的研究

本文以硝酸镉和硫脲为镉源和硫源,用溶剂热技术在乙二胺和水的混合溶剂中合成CdS/MWNTs复合材料;再以硝酸银和硫化钠为银源和硫源,十二烷基磺酸钠(SDS)为表面活性剂,以水为溶剂在室温下合成Ag2S/MWNTs复合材料并采用TEM、XRD对复合材料进行表征,结果表明:CdS纳米晶和Ag2S纳米粒子成功长到了多壁碳纳米...     

Au-Pt纳米颗粒/石墨烯-纤维素微纤维复合电极的制备与电化学性能

石墨烯和金属纳米是优异的导电纳米材料,为构建具有高效活性表面积的电化学传感界面,以玻碳电极作为导电基底,采用滴涂法结合一步电沉积成功制备了Au-Pt纳米颗粒/还原氧化石墨烯-纤维素微纤维(Au-Pt NPs/RGO-CMF)复合材料。SEM、原子力显微镜(AFM)、EDS和拉曼光谱分析表明,Au-Pt纳米颗粒均匀分布在RGO-CMF的薄层上,同时实现了氧化石墨烯(GO)还原为RGO。以铁氰化钾作为氧化还原探针对界面的电化学性质进行研究,在优化的实验条件下(循环伏安法电沉积:电位为?1.2~0 V,周期为20,电解质pH值为6,滴涂GO-CMF体积为8 μL),得到Au-Pt NPs/RGO-CMF复合材料的高效活性表面积(3.54 cm2)远远优于裸玻碳电极(1.52 cm2)。表明构建界面具有高的电催化活性,为传感器的进一步应用提供理论支持。      

多元醇方法制备SnO2包覆碳纳米管复合材料

本文采用SnC2O4.2H2O为Sn源和乙二醇(ethylene glycol,EG)为反应介质的多元醇法,制备得到SnO2包覆多壁碳纳米管复合材料(SnO2/MWNTs),其中SnO2是通过EG中溶解的O2氧化Sn2+反应生成的.没有加入MWNTs的情况下,SnC2O4.2H2O的水解反应生成Sn6O4(OH)4,SnC2O4.2H2O与EG之间的聚合反应生成聚羟基乙酸锡,由于水解反应降低了EG中Sn2+的浓度,使得聚羟基乙酸锡产量较低.加入MWNTs后,仅有少量聚羟基乙酸锡生成,且没有Sn6O4(OH)4生成,主要产物为包覆在MWNTs表面的SnO2.这是由于SnO2在EG中的溶解度极低,随O2氧化Sn2+反应进行,EG中的Sn2+浓度不断降低,Sn6O4(OH)4的溶解结晶平衡不断向溶解的方向进行,并最终转化为SnO2.以上对多元醇法制备SnO2/MWNTs合成机理的理解,将有助于采用类似的方法设计合理条件制备得到其他种类金属氧化物包覆碳纳米管的复合材料.     

Fast wave forms for pulsed electrochemical detection of glucose by incorporation of reductive desorption of oxidation products

The electrochemical activity of Au electrodes held at constant potential for anodic detection of carbohydrates in alkaline media eventually decays to zero. This loss of response is a consequence of the accumulation of adsorbed oxidation products on the electrode surface. Although it is well-known that these "poisons" can be removed by oxidative desorption simultaneously with formation of surface oxide, we have discovered that electrodes fouled during the detection of glucose yield a cathodic peak at -0.77 V vs SCE resulting from reductive desorption of these species. Incorporation of the reductive desorption process into wave forms for pulsed electrochemical detection (PED) permits a significant decrease in the time periods traditionally allowed for the oxidative and reductive reactivation of the electrode with a resulting increase in wave form frequency. A 6.7-Hz wave form using E(red) = -1.00 V (t(red) = 10 ms), E(oxd) = +0.60 V (t(oxd) = 10 ms), and E(det) = +0.10 V (t(del) = 50 ms, t(int) = 50 ms) is applied for detection of glucose in a LC-PED system and is demonstrated to yield a sub-picomole detection limit with a linear dynamic range extending over three decades.     

Si@环化聚丙烯腈/多壁碳纳米管负极复合材料的制备及电化学性能

通过简单高能球磨和高温热解法制备了锂离子电池Si/C电极复合材料,聚丙烯腈（PAN）包覆的纳米颗粒（Si@PAN）与多壁碳纳米管（MWCNTs）混合,制得Si@环化PAN/MWCNTs（Si@c-PAN/MWCNTs）复合材料作为锂离子电池的负极材料。包覆在纳米Si外层的高温热解后的PAN能够有效缓冲Si在充放电过程中巨大的体积变化产生的应力,同时MWCNTs作为Si@c-PAN的基体阻止Si@c-PAN颗粒的团聚,也提高了Si@c-PAN/MWCNTs复合材料电极的导电性能。电化学测试结果表明,Si@c-PAN/MWCNTs复合材料电极在电流密度为0.2 A/g时,其首次放电比容量达到2 098 mA?h/g,库伦效率达到86%;循环50次后Si@c-PAN/MWCNTs复合材料电极的可逆比容量仍能够达到1 278 mA?h/g,在2 A/g放电时其比容量为600 mA?h/g,仍保持良好的循环稳定性。      

Electrochemical behavior of gold nanoparticles modified nitrogen incorporated tetrahedral amorphous carbon and its application in glucose sensing

Gold nanoparticles (NPs) with 10-50 nm in diameter were synthesized on nitrogen incorporated tetrahedral amorphous carbon (ta-C:N) thin film electrode by electrodeposition. The deposition and nucleation processes of Au on ta-C:N surface were investigated by cyclic voltammetry and chronoamperometry. The morphology of Au NPs was characterized by scanned electron microscopy. The electrochemical properties of Au NPs modified ta-C:N (ta-C:N/Au) electrode and its ability to sense glucose were investigated by voltammetric and amperometric measurements. The potentiostatic current-time transients showed a progressive nucleation process and diffusion growth of Au on the surface of ta-C:N film according to the Scharifker-Hills model. The Au NPs acted as microelectrodes improved the electron transfer and electrocatalytic oxidation of glucose on ta-C:N electrode. The ta-C:N/Au electrode exhibited fast current response, a linear detection range of glucose from 0.5 to 25 mM and a detection limit of 120 microM, which hinted its potential application as a glucose biosensor.     

Electrochemical genosensor based on colloidal gold nanoparticles for the detection of Factor V Leiden mutation using disposable pencil graphite electrodes

Electrochemical genosensors for the detection of the Factor V Leiden mutation from polymerase chain reaction (PCR) amplicons using the oxidation signal of colloidal gold (Au) is described. A pencil graphite electrode (PGE) modified with target DNA, when hybridized with complementary probes conjugated to Au nanoparticles, responded with the appearance of a Au oxide wave at approximately +1.20 V. Specific probes were immobilized onto the Au nanoparticles in two different modes: (a) Inosine-substituted probes were covalently attached from their amino groups at the 5' end using N-(3-dimethylamino)propyl)-N'-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysulfosuccinimide (NHS) as a coupling agent onto a carboxylate-terminated l-cysteine self-assembled monolayer (SAM) preformed on the Au nanoparticles, and (b) probes with a hexanethiol group at their 5' phosphate end formed a SAM on Au nanoparticles. The genosensor relies on the hybridization of the probes with their complementary targets, which are covalently immobilized at the PGE surface. Au-tagged 23-mer capture probes were challenged with the synthetic 23-mer target, 131-base single-stranded DNA or denatured 256-base polymerase chain reaction (PCR) amplicon. The appearance of the Au oxidation signal shortened the assay time and simplified the detection of the Factor V Leiden mutation from PCR amplified real samples. The discrimination between the homozygous and heterozygous mutations was also established by comparing the peak currents of the Au signals. Numerous factors affecting the hybridization and nonspecific binding events were optimized. The detection limit for the PCR amplicons was found to be as low as 0.78 fmol; thus, it is suitable for point-of-care applications.     

Direct electrochemical determination of ascorbic acid by a cobalt(II) tetra-neopentyloxy phthalocyanine-multi-walled carbon nanotubes glassy carbon electrode

A cobalt(II) tetra-neopentyloxy phthalocyanine-multi-walled carbon nanotubes (CoTNPPc–MWNTs) composite was synthesized and characterized by UV–Vis spectra and transmission electron microscopy. The CoTNPPc–MWNTs glassy carbon electrode (CoTNPPc–MWNTs/GCE) was prepared by drop coating. The electrocatalytic performance of the chemically modified electrode was investigated for oxidation of ascorbic acid (AA). It was found that in phosphate buffer solution at pH = 6.60, the chemically modified electrode exhibited excellent electrocatalytic activity toward the oxidation of AA. The oxidation peak current increased linearly with the concentration of AA in the range of 10 μM–1.6 mM within the detection limit of 5 μM and low response time of 4 s.     

Electrochemical co-deposition of bimetallic Pt-Ru nanoclusters dispersed on poly(3,4-ethylenedioxythiophene) and electrocatalytic behavior for methanol oxidation

Nanoclusters of bimetallic Pt-Ru are electrochemically deposited on conductive polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), which is also electrochemically deposited on a carbon paper substrate. The bimetallic deposition is carried out in an acidic electrolyte consisting of chloroplatinic acid and ruthenium chloride at 0.0 V versus saturated calomel electrode (SCE) on PEDOT coated carbon paper. A thin layer PEDOT on a carbon paper substrate facilitates the formation of uniform, well-dispersed, nano clusters of Pt-Ru of mean diameter of 123 nm, which consist of nanosize particles. In the absence of PEDOT, the size of the clusters is about 251 nm, which are unevenly distributed on carbon paper substrate. Cyclic voltammetry studies suggest that peak currents of methanol oxidation are several times greater on PtRu-PEDOT electrode than on Pt-Ru electrode in the absence of PEDOT.     

A biomimetic phospholipid/alkanethiolate bilayer immobilizing uricase and an electron mediator on an Au electrode for amperometric determination of uric acid.

A biomimetic bilayer membrane immobilizing uricase (urate oxidase; EC 1.7.3.3) (UOx) and a redox agent of 1-methoxy-5-methylphenazinium (MMP) was fabricated on an Au electrode substrate with use of the Au substrate coated with a self-assembled monolayer of n-octanethiolate (OT/Au) and L-alpha-phosphatidylcholine beta-oleoyl-gamma-palmitoyl (PCOP). The preparation was carried out by successively immersing an Au electrode substrate in an ethanol solution of OT, an MMP aqueous solution, and a suspension of proteoliposome formed by PCOP containing UOx and MMP. The prepared electrode exhibited such fast steady amperometric responses to uric acid as to allow its determination within 20 s after injecting uric acid, indicating that UOx-catalyzed electrochemical oxidation of uric acid was accomplished with assistance of electron mediation by MMP between UOx and the Au substrate. An increase in the response currents with increasing concentration of uric acid was obtained in a concentration range of uric acid found in healthy human blood. Any interference in the current response that is caused by direct anodic oxidation of uric acid or ascorbic acid was not observed at the prepared sensor electrode because the densely packed bilayer effectively blocked the diffusion of these substrates toward the Au surface, making it possible to determine amperometrically uric acid at the electrode with high precision.     

Enhanced oxidation of diclofenac sodium at a nano-structured electrochemical sensing film constructed by multi-wall carbon nanotubes–surfactant composite

A multi-walled carbon nanotubes (MWNTs)–dihexadecyl hydrogen phosphate (DHP) film-coated glassy carbon electrode (GCE) was fabricated, and the voltammetric determination method of diclofenac sodium was investigated on this modified electrode by using different kinds of electrochemical techniques. The results showed that this nano-structured film electrode exhibits excellent enhancement effects on the electrochemical oxidation of diclofenac sodium. The oxidation peak current of diclofenac sodium at this film-modified electrode increased significantly compared with that at a bare glassy carbon electrode. Based on the experiment outcomes a possible mechanism was proposed and discussed. The proposed method was demonstrated by using diclofenac sodium tablets and the result was satisfying.     

Design of an Assembly of Poly(benzimidazole), Carbon Nanotubes,and Pt Nanoparticles for a Fuel‐Cell Electrocatalyst with an Ideal Interfacial Nanostructure

A newly designed and fabricated novel nanocomposite composed of multiwalled carbon nanotubes (MWNTs), poly(benzimidazole) (PBI), and Pt nanoparticles. This composite is fabricated by the preparation of PBI‐wrapped MWNTs (MWNT/PBI), followed by Pt loading onto the MWNT/PBI. As a result of the PBI wrapping, the loading efficiency of the Pt nanoparticles onto the MWNTs is dramatically improved up to 58.8% compared to that of the pristine MWNTs (41.0%). The process also allows homogeneous Pt immobilization onto the surface of MWNTs without any strong oxidation process for the MWNTs that is typically used for metal supporting on carbon nanotubes. Far‐IR spectroscopy of the composite shows a peak from the Pt? N bonding, indicating that these improvements are derived from the coordination of the Pt ion with the PBI molecules. Cyclic voltammogram measurements reveal that the Pt nanoparticles deposited on the MWNT/PBI shows higher utilization efficiency (74%) for electrocatalysts compared to that on the pristine MWNT (39%).     

流体组装制造的金属-碳纳米管-金属结构

基于碳纳米管的纳米器件制造中,金属-碳纳米管-金属结构是重要部分通过流体组装多壁碳纳米管,并在其上沉积、光刻图形化金属制造了金属-碳纳米管-金属结构．对比不同流体组装条件下的排列效果发现,较大的样品台倾角和较高的气流速度可实现较好的碳纳米管组装．通过对碳纳米管与金属间的接触电阻进行估算和比较,金属包覆碳纳米管比碳纳米管沉积在全电极上的接触方式具有更小的接触电阻和接触电阻分散性,且碳纳米管与金电极接触状态比钛电极好最终通过该方法制造出了接触良好的金属-碳纳米管-金属结构。     

Synthesis, characterization and electrocatalytic activity of fused gold nanoparticles

This paper describes the synthesis of fused spherical gold nanoparticles (AuNPs) and their electrocatalytic activity towards the oxidation of hydroxylamine (HA). Fused AuNPs were prepared by one-pot synthesis using 2-mercapto-4-methyl-5-thiazoleacetic acid (TAA) as a stabilizing agent and sodium borohydride (NaBH4) as a reducing agent. The HR-TEM images showed that two individual AuNP were joined via on its surface with a size range of approximately 7 nm and a length of approximately 15 nm diameter. The pH studies showed that the synthesized fused AuNPs was stable at pH > 8. This indicated that the carboxylate ion present on the TAA molecule stabilized the AuNPs from aggregation. Further, the fused AuNPs were utilized for the electrocatalytic oxidation of hydroxylamine (HA) after immobilized them on (3-mercaptopropyl)-trimethoxysilane (MPTS) sol-gel film modified Au electrode. The AuNPs modified electrode showed an excellent electrocatalytic activity towards the oxidation of HA in 0.2 M phosphate buffer solution (pH 7.2) by shifting its oxidation potential to 100 mV less positive and enhancing its oxidation current for more than three times when compared to bare Au electrode. Further, it was found that the fused AuNPs modified electrode showed greater electrocatalytic activity towards HA than the spherical AuNPs modified electrodes.     

Voltammetric determination of tryptophan at a single-wall carbon nanotubes modified electrode

A single-wall carbon nanotubes (SWNT)-film coated glassy carbon electrode (GCE) was described for the determination of tryptophan. In pH 2.5 Na2HPO4-citric acid buffer, tryptophan yields a well-defined and very sensitive oxidation peak at about 1.08 V at the SWNT-film coated GCE. The oxidation peak current increases greatly and the peak potential shifts toward more negative direction at the SWNT-modified GCE in contrast to that at the bare GCE. Under optimized conditions, the oxidation peak current is proportional to the concentration of tryptophan over the range from 4 x 10(-8) to 1 x 10(-5) mol/L. The detection limit is 1 x 10(-8) mol/L at 3 min of accumulation. Using the proposed method, tryptophan in the human's blood serum samples was determined.     

Electrochemical properties of carbon nanotube (CNT) film electrodes prepared by controllable adsorption of CNTs onto an alkanethiol monolayer self-assembled on gold electrodes

This paper describes electrochemical properties, such as electrode reactivity, electrode dimensions, and interfacial capacitance, of multiwalled carbon nanotube (MWNT) film electrodes prepared by controllable adsorption of the MWNTs onto the self-assembled monolayer (SAM) of n-octadecyl mercaptan (C18H37SH) deposited onto Au electrodes. The adsorption of the MWNTs onto the SAM-modified Au electrode substantially restores heterogeneous electron transfer between bare Au electrode and redox species in solution phase that is almost totally blocked by the SAM of C18H37SH, and as a result, the prepared MWNT/SAM-modified electrode possesses good electrode reactivity without a remarkable barrier to heterogeneous electron transfer. In addition, the surface coverage of the MWNTs is readily controlled by adjusting the immersion time for the adsorption of the MWNTs onto the SAM of C18H37SH, which essentially endows the prepared MWNT/SAM-modified electrodes with tunable electrode dimensions ranging from a nanoelectrode array to a macro-sized conventional electrode. On the other hand, the MWNT/SAM-modified electrode is found to possess a largely reduced interfacial capacitance, as compared with the MWNT film electrodes prepared with existing methods by directly confining the MWNTs onto electrode surface. This demonstration offers a new approach to fabrication of stable MWNT film electrodes with excellent electrochemical properties that are believed to be very attractive for electrochemical studies and electroanalytical applications.     

Electrochemical biosensor based on multi-walled carbon nanotubes and Au nanoparticles synthesized in chitosan

A new biosensor is prepared by cross-linking glucose oxidase (GOD) with glutaradehyde at the electrode combining Au nanoparticles (AuNP) with multi-walled carbon nanotubes (MWCNTs). Au nanoparticles-doped chitosan (CS) solution (AuNP-CS) is prepared by treating the CS solution followed by chemical reduction of Au (III) with NaBH4. MWCNTs are then dispersed in AuNP-CS solution. TEM, FT-IR, and UV-Vis show that the AuNP-CS solution is highly dispersed and stable. The synergistic effect between AuNP and CNTs of the AuNP-CNTs-CS material has been investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and amperometric methods. The modified glassy carbon electrode (GCE) allows low-potential detection of H2O2 with high sensitivity and fast response time. With the immobilization of GOD, a biosensor has been constructed. In phosphate buffer solutions (PBS, pH 7.0), nearly free interference determination of glucose has been realized at 0.4 V(vs. Ag/AgCl/3.0 M KCI) with a wide linear range from 2.0 x 10(-5) to 1.5 x 10(-2) M and a fast response time within 5s. The biosensor has been used to determine glucose in human serum samples and the results are satisfactory.     

Au纳米粒子/双层TiO2周期结构的制备及其对乙醇的电催化性质

利用二次阳极氧化法成功制备了双层TiO₂纳米管周期结构。通过改变氧化电压可以有效地调整双层TiO₂纳米管的管径, 从而控制样品的形貌。通过实验优化确定双层TiO₂周期结构的制备条件为一次氧化电压60 V, 二次氧化电压40 V。利用原位光还原法, 在TiO₂周期结构表面负载了Au纳米粒子并研究了前驱体溶液浓度与光照时间对样品的影响。在0.05 mmol/L HAuCl₄溶液中光照90 min后得到的Au纳米粒子具有最优的形貌与分布。这种绿色的原位光还原法因为避免使用保护剂与还原剂而有效提高了Au纳米粒子的催化活性。制备所得的Au/TiO₂周期异质结构可以直接作为工作电极用于乙醇的电催化氧化, 并表现出了良好的催化活性与稳定性。除了Au纳米粒子, 其他金属纳米粒子如Ag、Pd、Cu等均可通过该方法成功负载于双层TiO₂纳米管周期结构上。这种新型的异质结纳米结构作为燃料电池的阳极材料表现出了巨大的潜力。     

Application of Multi-walled Carbon Nanotubes/Nafion Composite Film in Electrochemical Determination of Pb2+

In this work, insoluble multi-walled carbon nanotubes (MWNTs) was dispersed into ethanol in the presence of 1% Nafion, resulting in a stable and well-distributed MWNTs/Nafion suspension characterized by TEM and particle size analyzer. After evaporation of ethanol, a uniform MWNTs/Nafion composite film-coated glassy carbon electrode (GCE) was prepared and then characterized with SEM. Furthermore, the electrochemical behavior of Pb²⁺ at the unmodified GCE, Nafion film-modified GCE and MWNTs/Nafion film-modified GCE was investigated. It was found that the reduction peak potential shifts positively and peak current remarkably increases at the MWNTs/Nafion film-modified GCE, suggesting that MWMTs/Nafion film-modified GCE exhibits catalytic ability to electrochemical reduction of Pb²⁺. Based on this, a sensitive and convenient electrochemical method was proposed for the determination of Pb²⁺. Finally, the MWMTs/Nafion film-modified GCE was successfully used to detect Pb²⁺ in a water sample.