Hsieh-Hsun Chung

Flow injection analysis of hydrogen peroxide on copper-plated screen-printed carbon electrodes

A disposable copper-plated screen-printed carbon electrode (CuSPE) was developed for the determination of hydrogen peroxide by flow injection analysis (FIA) at ambient temperature without deoxygenation. Cyclic voltammetry on the CuSPE in pH 7.4 phosphate buffer solution showed the growth of CuO and Cu2O. A well-defined reduction signal corresponding to the mediation of CuO and Cu2O occurred in the presence of hydrogen peroxide. The mechanistic study revealed that the reduction is a coupled-chemical reaction mechanism with the operation of pseudo-first order kinetics with respect to the concentration of Cu2O. The calculated electrochemical rate constant (ke) from Laviron’s model is 13.7 s−1. Systematic investigations were made to optimize the experimental parameters for hydrogen peroxide detection by FIA. With a poised potential of −0.3 V versus Ag/AgCl and a flow rate of 2 ml min−1, the calibration curve was found to be linear up to 200 μM hydrogen peroxide with a detection limit of 0.97 μM (S/N = 3). The CuSPE is fairly stable for repetitive measurements.

A disposable screen-printed silver strip sensor for single drop analysis of halide in biological samples

A screen-printed silver strip with three-electrode configuration of Ag-working, Ag-counter and Ag/Ag(x)O reference electrodes was developed for simultaneous determination of chloride, bromide and iodide in aqueous solutions. It was fabricated simply by screen-printing silver ink onto a polypropylene (PP) base. The in-situ prepared Ag/Ag(x)O reference electrode can avoid the leaching interference in chloride detection while using a conventional Ag/AgCl reference electrode. A single drop of analyte (50 microl) is enough to determine iodide, bromide and chloride by measuring the well-separated oxidation peak currents of respective silver halides. The calibration graph was linear from 10 microM to 20 mM for iodide and bromide and 100 microM to 20 mM for chloride and the detection limit (S/N=3) was 3.05 microM, 2.95 microM and 18.83 microM for iodide, bromide and chloride, respectively. The strip is designed to be disposable and as such manual polishing is not necessary. The proposed sensor is not only simple to manufacture and easy to operate but also fast and precise with little detection volume. It is successfully applied to the determination of halide ions in real samples.

Electrochemical impedance study and sensitivevoltammetric determination of Pb(II) at electrochemicallyactivated glassy carbon electrodes

An electrochemically oxidized glassy carbon electrode was found to work excellently in the trace determination of Pb(II) using square-wave anodic stripping voltammetry. The associated phenomena were unravelled using chronocoulometry, linear scan voltammetry and electrochemical impedance spectroscopy. The chronocoulometry results showed that the double layer charge enormously increased on preanodization due to the creation of phenolic and quinolic oxide functional groups on the surface. The ac impedance analysis indicated that the duplex-layer model could illustrate the oxidized glassy carbon electrode behaviour quantitatively. The experimental factors, including preanodization condition, square-wave parameter, supporting electrolyte and pH, were optimized. Using the optimum parameters, the calibration curve was constructed and the detection limit was found to be 0.7 ppb (S/N = 3). The electrode is quite stable for repetitive measurements. The practical application was demonstrated to estimate trace Pb(II) in groundwater with very good precision.

Determination of Codeine in Human Plasma and Drug Formulation Using a Chemically Modified Electrode

Both flow injection methodology and square-wave voltammetry were developed and evaluated for determining codeine in human plasma and pharmaceutical formulations using a Nafion/ruthenium oxide pyrochlore chemically modified electrode. Combining the electrocatalytic function of the ruthenium-oxide pyrochlore with charge-exclusion and the preconcentration features of Nafion perform well in codeine detection. Compared to a bare glassy carbon electrode, the chemically modified electrode exhibits a shift of the oxidation potential in cathodic direction and a marked enhancement of the current response. A linear calibration plot is obtained over the 0–32 μM range in 0.05 M HClO4 solution with a detection limit (3σ) of 10 nM in the square-wave voltammetric method. While, in flow-injection analysis, a linear calibration plot is obtained over the 0.5–40 μM range with a detection limit of 0.86 ng. Quantitative analysis was performed by the standard addition method for codeine content in human plasma and a commercially available drug.

Fabrication of a Glucose Biosensor Based on Inserted Barrel Plating Gold Electrodes

We demonstrate here the application of barrel plating gold electrodes for fabricating a new type of disposable amperometric glucose biosensor. It is prepared by inserting two barrel plating gold electrodes onto an injection molding plastic base followed by immobilizing with a bioreagent layer and membrane on the electrode surface. The primary function of barrel plating is to provide an economical way to electroplate manufactured parts. The manufacture procedure is simple and can increase the fabrication precision for automation in mass production. At the two-electrode system, the detection of glucose is linear up to 800 mg/dL (i.e., 44.5 mM, r(2) > 0.99) in pH 7.4 PBS with a sensitivity of 0.71 microA/mM. Excellent sensor-to-sensor reproducibility shows coefficients of variation of only 0.8-1.4% for the detection of 56.5-561.0 mg/dL glucose. In laboratory trials 176 capillary blood samples with a range of 30-572 mg/dL glucose are used to evaluate the clinical application of the biosensor. A good linear correlation is observed between the measured values of the proposed biosensor and laboratory reference. Error grid analysis verifies that the proposed technique is promising in fabricating biosensor strips on a mass scale. As successfully demonstrated by using whole blood glucose as a model analyte, the fabrication technique can extend into other barrel plating noble metal electrodes for various applications.