Determination of isatin and monoamine neurotransmitters in rat brain with liquid chromatography using palladium hexacyanoferrate modified electrode.

The fabrication and application of a novel electrochemical detector (ED) with palladium hexacyanoferrate (PdHCF) chemically modified electrode (CME) for liquid chromatography (LC) were described. The electrochemical behaviors of isatin, monoamine neurotransmitters and their metabolites at this CME were investigated by cyclic voltammetry. It was found that the CME exhibited efficiently electrocatalytic of isatin and showed high sensitivity and stability for determination of monoamine neurotransmitters. The linear ranges were over three orders of magnitude and the detection limits were 2.5 x 10(-8) mol L(-1) for isatin, 2.5 x 10(-10) mol L(-1) for norepinephrine (NE), 2.5 x 10(-10) mol L(-1) for 5-hydroxyindoleacetic acid (5-HIAA), 5.0 x 10(-10) mol L(-1) for dopamine (DA), 1.0 x 10(-9)mol L(-1) for 3,4-dihydroxyphenylacetic acid (DOPAC), 1.2 x 10(-10) mol L(-1) for 5-hydroxytryptamine (5-HT) and 2.5 x 10(-9)mol L(-1) for homovanillic acid (HVA). Combined with microdialysis, the method was successfully applied to study the effect of isatin on the levels of monoamine neurotransmitters in experimental Parkinsonian rats. The results showed that isatin could significantly increase striatal monoamine neurotransmitters release to the basal level.

ZnS quantum dots derived a reagentless uric acid biosensor.

A reagentless amperometric uric acid biosensor based on zinc sulfide (ZnS) quantum dots (QDs) was firstly developed. It could detect uric acid without the presence of an electron mediator. The carboxyl group functionalized ZnS QDs were synthesized, and they were soluble biocompatible and conductive. ZnS QDs conjugates could provide increased enzyme binding sites, which may result in higher enzyme loading. Thus, the proposed uricase/ZnS QDs/l-cys biosensor exhibited higher amperometric response compared to the one without QDs (uricase/l-cys biosensor). In addition, there was little AA interference. It showed a linear dependence on the uric acid concentration ranging from 5.0x10(-6) to 2.0x10(-3)molL(-1) with a detection limit of 2.0x10(-6)molL(-1) at 3sigma.

Assay for uric acid level in rat striatum by a reagentless biosensor based on functionalized multi-wall carbon nanotubes with tin oxide.

A novel reagentless amperometric uric acid biosensor based on functionalized multi-wall carbon nanotubes (MWCNTs) with tin oxide (SnO2) nanoparticles has been developed. This was successfully applied to assay uric acid levels from an in vivo microdialysis sampling. Compared with unfunctionalized or traditional carboxylic acid (-COOH)-functionalized MWCNTs, the MWCNTs-SnO2 electrode exhibited higher electrocatalytic oxidation to uric acid. Here, MWCNTs-SnO2 may act as an efficient promoter, and the system exhibited a linear dependence on the uric acid concentration over the range from 1.0 x 10(-7) to 5.0 x 10(-4) mol L(-1). In addition, there was little ascorbic acid interference. The high sensitivity of the MWCNTs-SnO2 modified enzyme electrode enabled the monitoring of trace levels of uric acid in dialysate samples in rat striatum.

Evaluation of an amperometric glucose biosensor based on a ruthenium complex mediator of low redox potential.

An amperometric glucose ring-disk biosensor based on a ruthenium complex mediator of low redox potential was fabricated and evaluated. This thin-layer radial flow microsensor (10mul) with ring-disk working electrode displayed remarkable amperometric sensitivity. For Ru(3)(mu(3)-O)(AcO)(6)(Py)(3)(ClO(4)) (Ru-Py), a trinuclear oxo-acetate bridged cluster, a reversible redox curve of low redox potential and narrow potential window (redox potentials were -0.190 and -0.106V versus Ag/AgCl wire, respectively) was observed, which is comparable to many reported mediators such as ferrocene derivatives and other ruthenium complexes. The glucose and hydrogen peroxide assays were carried out with this complex-modified electrode Ru-Py-HRP-GOx/Nafion. The sensitivity was obtained 24nA (15.4mAM(-1)cm(-2)) for 10muM glucose and 126 nA (160mAM(-1)cm(-2)) for 5muM H(2)O(2), respectively with a working potential at 0V versus Ag/AgCl. Ascorbic acid was studied as interference to the glucose assay. The application of 0V potential versus Ag/AgCl did not avoid the occurrence of the oxidation of ascorbic acid, however, the pre-coating of ascorbate oxidase on the disk part of the ring-disk working electrode efficiently pre-oxidized the ascorbic acid and hence eliminated its interference on the glucose response. The practical reliability was also evaluated by assaying the dialysate from the prefrontal cortex of Wistar rats.

Simultaneous assay of glucose, lactate, L-glutamate and hypoxanthine levels in a rat striatum using enzyme electrodes based on neutral red-doped silica nanoparticles.

An electrochemical method suitable for the simultaneous measurement of cerebral glucose, lactate, L-glutamate and hypoxanthine concentrations from in vivo microdialysis sampling has been successfully performed for the first time using a neutral red-doped silica (NRDS) nanoparticle-derived enzyme sensor system. These uniform NRDS nanoparticles (about 50 +/- 3 nm) were prepared by a water-in-oil (W/O) microemulsion method, and characterized by a TEM technique. The neutral red-doped interior maintained its high electron-activity, while the exterior nano-silica surface prevented the mediator from leaching out into the aqueous solution, and showed high biocompability. These nanoparticles were then mixing with the glucose oxidase (GOD), lactate oxidase (LOD), L-glutamate oxidase (L-GLOD) or xanthine oxidase (XOD), and immobilized on four glassy carbon electrodes, respectively. A thin Nafion film was coated on the enzyme layer to prevent interference from molecules such as ascorbic acid and uric acid in the dialysate. The high sensitivity of the NRDS modified enzyme electrode system enables the simultaneous monitoring of trace levels of glucose, L-glutamate, lactate and hypoxanthine in diluted dialysate samples from a rat striatum.

Platinum particles-modified electrode for HPLC with pulsed amperometric detection of thiols in rat striatum.

A new chemically modified electrode based on the immobilization of Pt particles is fabricated and exhibits electrocatalytic oxidation for L-cysteine (L-Cys), glutathione (GSH) and penicillamine (PEN) with relatively high sensitivity. It is also adaptable to HPLC for pulsed amperometric detection (PAD) of these thiols. PAD largely improves the detection sensitivity because the alternated polarizations can effectively clean and reactivate the electrode surface. It is shown that the peak currents of L-Cys, GSH and PEN are linear to their concentrations, with the calculated detection limit of 1.1 x 10(-7), 1.8 x 10(-7) and 3.8 x 10(-7) mol L(-1), respectively (S/N = 3). The method has been successfully applied to assess the contents of L-Cys and GSH in rat striatal microdialysates. The average contents of the two analytes in rat striatum are 2.6 x 10(-6) and 2.8 x 10(-6) mol L(-1), respectively.

Liquid chromatography with amperometric detection at a nano crystalline Ce-doped lead dioxide film modified electrode for determination of (R)-Salsolinol, (R)-N-methylsalsolinol and monoamine neurotransmitters in Parkinsonian patients' cerebrospinal fluid.

The fabrication and application of a novel electrochemical detector (ED) with nano crystalline Ce-doped lead dioxide film chemically modified electrode (CME) for liquid chromatography (LC) were described. The Ce-doped PbO(2) film was characterized by X-ray diffractometer (XRD) and scanning tunnel microscope (STM). The electrochemical behaviors of (R)-Salsolinol ((R)-Sal) at the CME were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). It was found that the CME exhibited an efficiently electrocatalytic effect on the current responses of (R)-Sal, (R)-N-methylsalsolinol ((R)-NMSal) and monoamine neurotransmitters. In LC-ED, all (R)-Sal, (R)-NMSal, dopamine (DA), norepinephrine (NE), 3-methoxy-4-hydroxyphenylglycol (MHPG), 3,4-dihydroxyphenylacetic acid (DOPAC), 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA) had good and stable current responses at the CME. The linear ranges of the nine analytes were over three orders of magnitude (R(2) > 0.995). The application of this method coupled with microdialysis sampling for the determination of (R)-Sal, (R)-NMSal and monoamine neurotransmitters in Parkinsonian patients' cerebrospinal fluid (CSF) was satisfactory.

On-line biosensors for simultaneous determination of glucose, choline, and glutamate integrated with a microseparation system.

An effective microseparation system integrated with ring-disc electrodes and two microfluidic devices was fabricated for in vivo determination using a microdialysis pump. The major interference of ascorbic acid (AA) was excluded by direct oxidation with ascorbate oxidase. Glucose, glutamate, and choline were successfully determined simultaneously through the biosensors modified with a bilayer of osmium-poly(4-vinylpyridine)gel-horseradish peroxidase (Os-gel-HRP)/glucose oxidase (GOD), glutamate oxidase (GlutaOD) or choline oxidase (ChOD). To stabilize the biosensors, 0.2% polyethylenimine (PEI) was mixed with the oxidases. The cathodic currents of glucose, glutamate, and choline biosensors started to increase after the standard solutions were injected into the microseparation system. The on-line biosensors show a wide calibration range (10(-7)-10(-5) mol/L) with a detection limit of 10(-8) mol/L at the working potential of -50 mV. The variations of glucose, glutamate, and choline were determined simultaneously in a free moving rat when we perfused the medial frontal cortex with 100 micro mol/L N-methyl-D-aspartate (NMDA) solution, which is the agonist of the NMDA receptor.

Study of the interaction of 6-mercaptopurine with protein by microdialysis coupled with LC and electrochemical detection based on functionalized multi-wall carbon nanotubes modified electrode.

Microdialysis sampling coupled with liquid chromatography and electrochemical detection (LC-ECD) was developed and applied to study the interaction of 6-Mercaptopurine (6-MP) with bovine serum albumin (BSA). In the LC-ECD, the multi-wall carbon nanotubes fuctionalized with carboxylic groups modified electrode (MWNT-COOH CME) was used as the working electrode for the determination of 6-MP. The results indicated that this chemically modified electrode (CME) exhibited efficiently electrocatalytic oxidation for 6-MP with relatively high sensitivity, stability and long-life. The peak currents of 6-MP were linear to its concentrations ranging from 4.0 x 10(-7) to 1.0 x 10(-4) mol l(-1) with the calculated detection limit (S/N = 3) of 2.0 x 10(-7) mol l(-1). The method had been successfully applied to assess the association constant (K) and the number of the binding sites (n) on a BSA molecular, which calculated by Scatchard equation, were 3.97 x 10(3) mol(-1) l and 1.51, respectively. This method provided a fast, sensible and simple technique for the study of drug-protein interactions.

Study of carbon nanotubes-HRP modified electrode and its application for novel on-line biosensors.

In this paper, multi-walled carbon nanotubes (MWCNTs) were successfully immobilized on the surface of a glassy carbon electrode by mixing with horse-radish peroxidase (HRP). The electrochemical behavior of H2O2 was also studied with the MWCNTs-HRP modified electrode as a working electrode. The MWCNTs-HRP modified electrode showed excellent response of reduction current for the determination of H2O2 at the potential of -300 mV (vs. Ag/AgCl). We assembled the MWCNTs-HRP modified electrode in a thin-layer flow cell and the H2O2 solution was continuously introduced into the cell with a syringe pump. We optimized the sensitivity of the H2O2 sensor by adjusting the working potential and the pH of the buffer solution. The peak current increased linearly with the concentration of H2O2 in the range 3.0 x 10(-7) to approximately 2.0 x 10(-4) mol L(-1). The detection limit is 1.0 x 10(-7) mol L(-1) (S/N = 3). The interferences from ascorbic acid, uric acid and other electroactive substances can be greatly excluded since the sensor can be operated at -300 mV. Stability and reproducibility of the MWCNTs-HRP chemically modified electrode were also studied in this paper. Fabricated with glucose and lactate oxidase, the MWCNTs-HRP electrode was also applied to prepare the on-line glucose and lactate biosensors because of the high sensitivity for the determination of H2O2.

Amperometric determination of 6-mercaptopurine on functionalized multi-wall carbon nanotubes modified electrode by liquid chromatography coupled with microdialysis and its application to pharmacokinetics in rabbit.

In this paper, multi-wall carbon nanotubes functionalized with carboxylic groups modified electrode (MWNT-COOH CME) was fabricated. This chemically modified electrode (CME) can be used as the working electrode in the liquid chromatography for the determination of 6-mercaptopurine (6-MP). The results indicate that the CME exhibits efficiently electrocatalytic oxidation for 6-MP with relatively high sensitivity, stability and long-life. The peak currents of 6-MP are linear to its concentrations ranging from 4.0 x 10(-7) to 1.0 x 10(-4) mol l(-1) with the calculated detection limit (S/N=3) of 2.0 x 10(-7) mol l(-1). Coupled with microdialysis, the method has been successfully applied to the pharmacokinetic study of 6-MP in rabbit blood. This method provides a fast, sensible and simple technique for the pharmacokinetic study of 6-MP in vivo.

Continuous on-line measurement of cerebral hydrogen peroxide using enzyme-modified ring-disk plastic carbon film electrode.

An amperometric method suitable for the continuous on-line measurement of cerebral hydrogen peroxide from a microdialysate has been successfully performed for the first time by using an enzyme-modified ring-disk plastic carbon film electrode (PCFE) in a thin-layer radial flow cell. PCFE consists of a ring electrode modified with horseradish peroxidase to detect H2O2 at 0.0 V (vs Ag/ AgCl) and a disk electrode coated with ascorbate oxidase (AOx) to preoxidize ascorbic acid (AA) and thus suppress interference via direct oxidation. Analytes in solution (brain dialysates or standards) are mixed on-line with a phosphate-buffered solution containing dissolved oxygen and chelating agent, EDTA. The buffered solution is used to provide the O2 necessary for the AOx catalytic reaction, stabilize the changes in dialysate pH that are associated with the in vivo formation of H2O2, and remove heavy metal ion impurities and thus suppress reactions between AA and H2O2. This procedure enables trace levels of H2O2 to be readily monitored, virtually interference-free from physiological levels of AA, uric acid, electroactive neurotransmitters and their principle metabolites, in a continuous-flow system.