Jian-Jun Sun

Highly enhanced electrocatalytic oxidation of glucose and shikimic acid at a disposable electrically heated oxide covered copper electrode

A heated oxide covered copper electrode (HOCE) was facilely fabricated for the first time, providing a highly enhanced electrocatalytic oxidation, and cost effective and sensitive determination for polyhydroxy compounds such as glucose and shikimic acid.

Catalytic electrogenerated chemiluminescence and nitrate reduction at CdS nanotubes modified glassy carbon electrode.

Electrochemical and electrogenerated chemiluminescence (ECL) properties of a glassy carbon electrode modified with CdS nanotubes (CdS-GCE) are investigated in neutral media. The cyclic voltammogram (CV) shows two cathodic peaks (P(C1) and P(C2)) at -0.76 and -0.97 V and an anodic peak (P(A)) at -0.8 V, while two ECL peaks around -0.76 V are observed. Similar mechanisms of both ECLs are supposed and possibly related to the capture of an electron at a surface trap, that is, the surface sulfide vacancy (V(S)(2+)) of CdS nanotubes and its electrocatalytic reduction to H(2)O(2) generated from the dissolved oxygen. P(C2) and P(A) are ascribed to the two-electron redox at V(S)(2+). Moreover, electrocatalysis to nitrate reduction is also found at P(C2), with a good linear relationship between nitrate concentration and electrocatalytic peak current in CV.

Electrochemiluminescent Biosensor for Hypoxanthine Based on the Electrically Heated Carbon Paste Electrode Modified with Xanthine Oxidase

A new electrochemiluminescent (ECL) biosensor based on an electrically heated carbon paste electrode (HCPE) that was surface modified by xanthine oxidase (XOD) was designed and constructed in this work. It was found that the ECL intensity of luminol could be enhanced at the surface of XOD/HCPE by adding hypoxanthine (HX) to the solution, and there was a linear relationship between the ECL intensity and the concentration of HX. On the basis of this, an ECL enzyme biosensor can thus be developed to detect HX. However, because the activity of XOD is highly dependent on temperature, the biosensor is very sensitive to the temperature of the electrode. Also, because the temperature of the electrode may also affect the diffusion and convection of the luminescent compounds near the electrode surface, a suitable temperature for XOD/HCPE has to be controlled to achieve the best ECL signal. The key feature of the designed biosensor is that the temperature of the electrode is controllable so the most suitable temperature for the enzyme reaction can be obtained. The obtained results showed that the ECL enzyme biosensor exhibited the best sensitivity at an electrode temperature of 35 degrees C for the detection of HX. The detection limit was 30-fold lower than that at room temperature (25 degrees C).

Rapid hydrolysis and electrochemical detection of trace carbofuran at a disposable heated screen-printed carbon electrode

A disposable heated screen-printed carbon electrode (HSPCE) is successfully fabricated. It demonstrates rapid responses to electrical heating and is easily elevated above the water boiling point by a high frequency alternating current. The temperature rise at the HSPCE was found to be strongly dependent on the square of the heating current and the electrode width. Carbofuran (CAF) could be rapidly hydrolyzed to carbofuran phenol at the HSPCE with raised temperature, and then determined at the same electrode at room temperature by differential potential voltammetry (DPV). The factors influencing the detection were examined, including pH, hydrolytic temperature and heating time. Under the optimum conditions, the detection linear range of CAF was from 4.0 x 10(-7) to 4.0 x 10(-4) mol L(-1) and the detection limit was 5.0 x 10(-8) mol L(-1) (S/N = 3). This method was successfully applied to the analysis of CAF residues in real samples (spiked water, soil and vegetables), and satisfactory recoveries were obtained.

Gold nanoparticles for highly sensitive and selective copper ions sensing—old materials with new tricks

We report a new application of gold nanoparticles for visual detection of copper ions with high sensitivity and selectivity based on the colorimetric difference due to the strong and specific inhibition of Cu(NH3)62+ to the corrosion of gold nanoparticles at low concentration.

Electrodeposition of Mirror-Bright Silver in Cyanide-Free Bath Containing Uracil as Complexing Agent Without a Separate Strike Plating Process

A cyanide-free silver plating bath containing uracil as a complexing, agent was investigated. The electrochemical properties of a silver complex were studied on a disk glassy carbon electrode by means of cyclic voltammetry and a rotating disk electrode. The brightness and adhesion of silver deposits obtained from this silver plating bath onto copper substrates in the absence and presence of polyethyleneimine (PEI) were evaluated. Mirror-bright and good adherent silver deposits could be obtained without a separate strike plating process when PEI as an additive was added. Differential capacitance studies indicated that competition adsorption between PEI and uracil molecules occurred on the silver surface. The electrochemical displacement rate of silver by base metal (e.g., copper.) was very slow compared with that in it typical cyanide strike bath from the results of electrochemical quartz crystal microbalance studies. The surface morphology of silver deposits characterized by scanning electron microscopy illustrated that, with the addition of PEI, the grain size of the deposits decreased from hundreds to tens of nanometers

Electrocatalytic oxidation and nanomolar detection of hydrazine by luteolin electrodeposited at a multi-walled carbon nanotube and ionic liquid composite modified screen printed carbon electrode

A new electrode was fabricated by electrodepositing luteolin at a screen printed carbon electrode (SPCE) modified with a composite of multi-walled carbon nanotube (MWNT) and ionic liquid (IL). Cyclic voltammograms of the modified electrode in phosphate buffer solution showed a pair of stable and reversible redox couple of luteolin with surface confined characteristics. This electrode possessed excellent electrocatalytic ability towards hydrazine oxidation. The overpotential was decreased significantly and the peak current was increased dramatically compared to those at bare SPCE. This enhancement of the responses was mainly contributed to the combination of the unique electrocatalytic and electronic properties of luteolin, MWNT and IL. The modified electrode was employed to the amperometric detection of hydrazine at an applied potential of 0.31 V vs. SCE with fast response, high sensitivity, good stability and reproducibility. Two linear ranges of hydrazine were from 2.0 × 10−8 to 2.0 × 10−7 M and from 2.0 × 10−7 to 1.2 × 10−4 M. Nanomolar detection limit of 6.6 × 10−9 M (S/N = 3) could be obtained, which is at least one magnitude lower than any others with electrochemical detection of hydrazine. The proposed method was also used to determine hydrazine residues in spiked drinking water and river water with average recoveries of 101.7% and 101.1%, respectively.

Highly sensitive detection of silybin based on adsorptive stripping analysis at single-sided heated screen-printed carbon electrodes modified with multi-walled carbon nanotubes with direct current heating.

A new disposable multi-walled carbon nanotubes modified single-sided heated screen-printed carbon electrode (MWNT/ss-HSPCE) was fabricated. The electrochemical behavior of silybin was investigated by cyclic voltammetry and the probable electrode reaction mechanism was proposed. A simple and cheap direct current heating supplier was used to heating the electrode for adsorptive accumulation of silybin. The square wave voltammetric stripping peak current of silybin at MWNT/ss-HSPCE with an elevated electrode temperature of 50°C only during accumulation step was dramatically improved compared with that at bare single-sided heated screen-printed carbon electrode (ss-HSPCE) without heating. This enhancement was mainly contributed to the combination of the advantages of multi-walled carbon nanotubes and electrically heated electrodes. Under optimum conditions, two detection linear ranges of silybin were from 1.0×10(-9) to 1.0×10(-7) M and 3.0×10(-7) to 1.0×10(-6) M. A detection limit of 5.0×10(-10) M could be obtained (S/N=3), which was more than two magnitudes lower than that at bare ss-HSPCE without heating. To the best of our knowledge, this was also at least two magnitudes lower than any others for electrochemical detection of silybin in the literature. Finally, the method was successfully applied to the determination of silybin in pharmaceutical tablets.

Facile Electrochemical Preparation of Ag Nanothorns and Their Growth Mechanism

National Science Foundation of China [20775015, 211735002, 20975022]; National Basic Research Program of China [2010CB732403]; MOE [20070386005]; NCETTFJ [XSRC2007-02]; State Key Laboratory of Physical Chemistry of Solid Surfaces of Xiamen University

An extremely stable and sensitive end-column electrochemical detector based on heated copper microdisk electrode with direct current for CE and CE-Chip

A heated copper microdisk electrode (HCME) was fabricated and successfully applied to capillary electrophoresis (CE) and CE-Chip as an electrochemical detector (ECD) for the detection of three carbohydrates and shikimic acid (SA) in Illicium verum Hook F., respectively. The temperature of HCME was heated by twin-wire-wound coil with direct current to reduce the magnetic interference. Coupled with CE and CE-chip, this detector exhibits both extremely stable and sensitive performance at elevated temperature compared with that at room temperature. In successive detection of three carbohydrates and shikimic acid (SA), the HCME exhibits very stable response with RSD of ca. 2% with elevated temperature without renewing the electrode, while at room temperature, RSD of ca. 20% is obtained. This is very important in practical applications that tedious works, such as polishing and re-fixing the electrode at each detection, can be therefore avoided. In addition, the sensitivity is about 2-6 time increased, and the linear range is about an order wider at elevated temperature (ca. 60 degrees C) than that at room temperature (ca. 25 degrees C).