Copper sulfide nanoparticle-decorated graphene as a catalytic amplification platform for electrochemical detection of alkaline phosphatase activity.

Copper sulfide nanoparticle-decorated graphene sheet (CuS/GR) was successfully synthesized and used as a signal amplification platform for electrochemical detection of alkaline phosphatase activity. First, CuS/GR was prepared through a microwave-assisted hydrothermal approach. The CuS/GR nanocomposites exhibited excellent electrocatalytic activity toward the oxidation of ALP hydrolyzed products such as 1-naphthol, which produced a current response. Thus, a catalytic amplification platform based on CuS/GR nanocomposite for electrochemical detection of ALP activity was designed using 1-naphthyl phosphate as a model substrate. The current response increased linearly with ALP concentration from 0.1 to 100 U L(-1) with a detection limit of 0.02 U L(-1). The assay was applied to estimate ALP activity in human serum samples with satisfactory results. This strategy may find widespread and promising applications in other sensing systems that involves ALP.

[Electrocatalytic oxidation of SMZ at multi-wall carbon nanotubes-Nafion modified glassy carbon electrode and its electrochemical determination application].

Electrochemical behaviors, electrochemical kinetics and electrochemical determination of sulfamethoxazole (SMZ) at both glassy carbon electrode (GCE) and multi-wall carbon nanotubes-Nafion modified glassy carbon electrode (MWCNTs-Nafion/GCE) were investigated by cyclic voltammetry (CV), chronocoulometry (CC), chronoamperometry (CA), linear scan voltammetry (LSV) and amperometric i-t curve. The experimental results showed that the electrochemical oxidation of SMZ was sluggish on GCE, but the oxidation peak current of SMZ increased significantly at MWCNTs-Nafion/GCE in comparison with that at the bare GCE, which indicated that MWCNTs-Nafion/GCE could catalyze the electrochemical oxidation of SMZ very well. The plot of oxidation peak currents versus the square roots of the scanning rates for the redox in the potential range of 10-1,000 mV x s(-1) showed a straight line, as expected for a diffusion-limited electrochemical process for SMZ electrochemical oxidation. At the bare GCE and MWCNTs-Nafion/GCE the oxidation peak current was linearly proportional to the concentration of SMZ over the concentration range 5.0 x 10(-5)-2.5 x 10(-3) mol x L(-1) and 1.0 x 10(-5)-6.0 x 10(-3) mol x L(-1). The detection limits were 1.0 x 10(-5) and 5.0 x 10(-7) mol x L(-1). The relative standard deviation was between 0.85% -1.98% and the recovery was in the range of 98%-101.2%. This MWCNTs-Nafion/GCE could be applied in SMZ electrochemical determination with satisfied results. The proposed method can be applied to the determination of SMZ in tablet samples with satisfied results.

[Electrocatalytic oxidation of glutathione at 10-methylphenothiazine modified carbon paste electrode and its practical analytical application].

The electrocatalytic oxidation of glutathione (reduced form GSH) at 10-methylphenothiazine (MPT) modified carbon paste electrode (MPT/CPE) was investigated by cyclic voltammetry (CV). Although GSH itself showed a very poor electrochemical response at carbon paste electrode (CPE), the response could be greatly enhanced by using MPT/CPE, which enables a sensitive electrochemical determination of the substrate GSH. The reaction rate constant for catalytic oxidation was evaluated as (5.44 +/- 0.03) x 10(2) (mol L(-1))(-1) s(-1) by using chronoamperometry (CA). The catalytic oxidation peak current of GSH versus its concentration had a good linear relationship in the concentration range of 5.0 x 10(-6) - 2.0 x 10(-3) mol L(-1) with the correlation coefficient of 0.9990, and the detection limit of 1.0 x 10(-6) mol L(-1) by linear sweep voltammetry (LSV). The method can be applied for the determination of GSH in injection samples with the satisfactory results.

[Electrochemical behavior of dopamine at dodecyl benzenesulfonate self-assembled monolayers modified electrode and its application].

Sodium dodecyl benzenesulfonate (SDBS) self-assembled monolayers in situ modified electrode (SDBS/CPE) was prepared. The electrochemical behaviors of dopamine (DA) on SDBS/CPE were studied. Electrochemical behaviors and kinetic parameters of DA were investigated at SDBS/CPE by cyclic voltammetry (CV), chronoamperometry (CA) and chronocoulometry (CC). The changes of the oxidation peak currents with concentration of DA were examined by square wave voltametry (SWV). The difference of peak potential at CPB/CPE was less than 149 mV comparing with that at CPE. The charge transfer coefficient alpha, diffusion coefficient D and the apparent reaction rate constant k(f) are 0.61, 3.6 x 10(-5) cm2 x s(-1) and 4.2 x 10(-3) cm x s(-1), respectively. The oxidation peak currents of DA versus its concentration have a good linear relationship in the concentration range of 2.0 x 10(-6)-1.0 x 10(-3) mol x L(-1) with the correlation coefficient of 0.9979 and the detection limit of 9.0 x 10(-7) mol x L(-1) by square wave voltammetry (SWV) response. The modified electrode showed an excellent electrocatalytic activity for the DA electrochemical oxidation. The method can be applied in the determination of DA in injection samples with the satisfactory results.

Electrochemical oxidation of isoniazid catalyzed by (FcM)TMA at the platinum electrode and its practical analytical application.

The electrocatalytic oxidation of isoniazid (INH) by (ferrocenylmethyl)trimethylammonium [(FcM)TMA] at the platinum electrode in 0.10 M Na2SO4 aqueous solution was studied by cyclic voltammetry (CV). Although INH itself showed a very poor electrochemical response at the platinum electrode, the response could be greatly enhanced by using (FcM)TMA as a mediator, which enables a sensitive electrochemical determination of the substrate INH. The reaction rate constant for catalytic oxidation reaction was evaluated as (3.98+/-0.10)x10(3) M(-1) s(-1) by using chronoamperometry (CA). Experimental conditions such as supporting electrolyte and its concentration, solution pH, and the concentrations of the catalyst (FcM)TMA and the substrate INH were investigated to maximize the current efficiency of the electrocatalytic oxidation. The method can be used for the sensitive practical determination of INH, and also opens an avenue for using (FcM)TMA as a mediator in electroanalytical determination which is very simple, cheap, and rapid. Furthermore, no sample pretreatment or time-consuming extraction steps are required prior to the analysis.

Influence of micelles on the electrochemical behaviors of catechol and hydroquinone and their simultaneous determination.

A simple and highly selective electrochemical method for the simultaneous determination of CAT and HQ at a glassy carbon electrode in micellar solutions has been developed. The electrochemical behaviors of CAT and HQ in aqueous CPB and SDBS micellar solutions have been studied by cyclic voltammetry. The oxidation peak potentials shift negatively, the reduction peak potentials shift positively, and the peak currents increase in the presence of CPB for both CAT and HQ. However, the oxidation peak potentials shift positively, the reduction peak potentials shift negatively, and the peak currents decrease in the presence of SDBS for both CAT and HQ. The electrochemical kinetic parameters for CAT and HQ in aqueous CPB and SDBS micellar solutions were also determined by chronocoulometry (CC) and chronoamperometry (CA). The cyclic and pulse differential voltammetric behaviors of the system consisting of CAT coexisting with HQ were also investigated in this work. It was found that the oxidation peak potential waves of CAT and HQ were separated by 100 mV in the presence of CPB in 0.10 M PBS (pH 6.8). Therefore, CAT and HQ can be determined simultaneously in such a system. This simple method was applied to the simultaneous determination of HQ and CAT in a household tap water sample and it exhibited high selectivity.

[Study on direct electrochemical behaviors and the electroanalytical method of matrine type alkaloids at glassy carbon electrode].

OBJECTIVE: To investigate the direct electrochemical behaviors of matrine (MT), oxymatrine (OMT), sophoridine (SR) and oxysophoridine (OSR) at a glassy carbon electrode in a physiological medium, and to determine the contents of commercial MT and SR pharmaceutical products were determined. METHOD: Their electrochemical behaviors and contents in 0.15 mol x L(-1) NaCl aqueous solutions were obtained by cyclic voltammetry (CV) and square wave voltammetry (SWV) methods. RESULT: The electrochemical experimental results show that the two totally irreversible oxidation peaks for both MT and SR were observed, which potential values are 0.81 V and 0.92 V, and the electrode reaction processes were diffusion-controlled. But for both OMT and OSR, they have no oxidation peaks observed in the same condition as well. The linear range of the concentration of MT and SR and the contents in their products were obtained by SWV. CONCLUSION: The research results can be applied in determination of the contents of commercial MT and SR pharmaceutical products.

[Study on electrochemical kinetics of matrine and sophoridine in a physiological medium].

OBJECTIVE: To investigate the kinetic processes of direct electrooxidation for both matrine and sophoridine in a physiological medium. METHOD: Their direct electrooxidative behaviors and the parameters of electrochemical kinetics were obtained by cyclic voltammetry (CV), bulk electrolysis with coulometry, chronocoulometry (CC), chronoamperometry (CA). RESULT AND CONCLUSION: The electrochemical experimental results show that the two totally irreversible oxidation peaks in the region of 0.3-1.2 V vs SCE for both MT and SR were observed, and the electrode reactions processes were diffusion-controlled. Their electron transfer number n and electron transfer coefficient alpha were obtained by CV and electrolysis with coulometry. The diffusion coefficient D and rate constant kf were also calculated by CC and CA.