Highly ordered mesoporous carbons as electrode material for the construction of electrochemical dehydrogenase- and oxidase-based biosensors

In this work, the excellent catalytic activity of highly ordered mesoporous carbons (OMCs) to the electrooxidation of nicotinamide adenine dinucleotide (NADH) and hydrogen peroxide (H(2)O(2)) was described for the construction of electrochemical alcohol dehydrogenase (ADH) and glucose oxidase (GOD)-based biosensors. The high density of edge-plane-like defective sites and high specific surface area of OMCs could be responsible for the electrocatalytic behavior at OMCs modified glassy carbon electrode (OMCs/GE), which induced a substantial decrease in the overpotential of NADH and H(2)O(2) oxidation reaction compared to carbon nanotubes modified glassy carbon electrode (CNTs/GE). Such ability of OMCs permits effective low-potential amperometric biosensing of ethanol and glucose, respectively, at Nafion/ADH-OMCs/GE and Nafion/GOD-OMCs/GE. Especially, as an amperometric glucose biosensor, Nafion/GOD-OMCs/GE showed large determination range (500-15,000mumoll(-1)), high sensitivity (0.053nAmumol(-1)), fast (9+/-1s) and stable response (amperometric response retained 90% of the initial activity after 10h stirring of 2mmoll(-1) glucose solution) to glucose as well as the effective discrimination to the possible interferences, which may make it to readily satisfy the need for the routine clinical diagnosis of diabetes. By comparing the electrochemical performance of OMCs with that of CNTs as electrode material for the construction of ADH- and GOD-biosensors in this work, we reveal that OMCs could be a favorable and promising carbon electrode material for constructing other electrochemical dehydrogenase- and oxidase-based biosensors, which may have wide potential applications in biocatalysis, bioelectronics and biofuel cells.     

Bimetallic PtM (M=Pd, Ir) nanoparticle decorated multi-walled carbon nanotube enzyme-free, mediator-less amperometric sensor for H₂O₂

A new highly catalytic and intensely sensitive amperometric sensor based on PtM (where M=Pd, Ir) bimetallic nanoparticles (NPs) for the rapid and accurate estimation of hydrogen peroxide (H(2)O(2)) by electrooxidation in physiological conditions is reported. PtPd and PtIr NPs-decorated multiwalled carbon nanotube nanocatalysts (PtM/MWCNTs) were prepared by a modified Watanabe method, and were characterized by XRD, TEM, ICP, and XAS. The sensors were constructed by immobilizing PtM/MWCNTs nanocatalysts in a Nafion film on a glassy carbon electrode. Both PtPd/MWCNTs and PtIr/MWCNTs assemblies catalyzed the electrochemical oxidation of H(2)O(2). Cyclic voltammetry characterization measurements revealed that both the PtM (M=Pd, Ir)/MWCNTs/GCE possessed similar electrochemical surface areas (～0.55 cm(2)), and electron transfer rate constants (～1.23 × 10(-3)cms(-1)); however, the PtPd sensor showed a better performance in H(2)O(2) sensing than did the PtIr counterpart. Explanations were sought from XAS measurements to explain the reasons for differences in sensor activity. When applied to the electrochemical detection of H(2)O(2), the PtPd/MWCNTs/GC electrode exhibited a low detection limit of 1.2 μM with a wide linear range of 2.5-125 μM (R(2)=0.9996). A low working potential (0V (SCE)), fast amperometric response (<5s), and high sensitivity (414.8 μA mM(-1)cm(-2)) were achieved at the PtPd/MWCNTs/GC electrode. In addition, the PtPd/MWCNTs nanocatalyst sensor electrode also exhibited excellent reproducibility and stability. Along with these attractive features, the sensor electrode also displayed very high specificity to H(2)O(2) with complete elimination of interference from UA, AA, AAP and glucose.     

Construction and application of an amperometric xanthine biosensor based on zinc oxide nanoparticles-polypyrrole composite film

Zinc oxide nanoparticles (ZnO-NPs) were synthesized from zinc nitrate by simple and efficient method in aqueous media at 55°C without any requirement of calcinations step. A mixture of ZnO-NPs and pyrrole was eletropolymerized on Pt electrode to form a ZnO-NPs-polypyrrole (PPy) composite film. Xanthine oxidase (XOD) was immobilized onto this nanocomposite film through physiosorption. The ZnO-NPs/polypyrrole/Pt electrode was characterized by Fourier transform infrared (FTIR), cyclic voltammetry (CV), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electrochemical impedance spectroscopy (EIS) before and after immobilization of XOD. The XOD/ZnO-NPs-PPy/Pt electrode as working electrode, Ag/AgCl as reference electrode and Pt wire as auxiliary electrode were connected through a potentiostat to construct a xanthine biosensor. The biosensor exhibited optimum response within 5s at pH 7.0, 35°C and linearity from 0.8 μM to 40 μM for xanthine with a detection limit 0.8 μM (S/E=3). Michaelis Menten constant (K(m)) for xanthine oxidase was 13.51 μM and I(max) 0.071 μA. The biosensor measured xanthine in fish meat and lost 40% of its initial activity after its 200 uses over 100 days, when stored at 4°C.     

A novel and simple route to prepare a Pt nanoparticle-loaded carbon nanofiber electrode for hydrogen peroxide sensing

A facile wet-chemical method was developed to prepare a novel Pt nanoparticle-loaded carbon nanofiber (Pt/CNF) electrode. Without using any stabilizer or pretreatment procedure, large amounts of Pt nanoparticles could be well deposited on the surface of the electrospun CNF electrode at room temperature, as revealed by scanning electron microscopy (SEM). The effect of the precursor concentration on the formation of Pt catalysts was investigated to optimize the performance of the proposed hybrid electrode. When applied to the electrochemical detection of hydrogen peroxide (H?O?), the Pt/CNF electrode exhibited low overpotential, fast response and high sensitivity. A low detection limit of 0.6 μM with wide linear range of 1-800 μM (R=0.9991) was achieved at the Pt/CNF electrode, which was superior to that obtained with other H?O? electrochemical sensors reported previously. In addition, the Pt/CNF electrode showed good selectivity for H?O? detection in the presence of ascorbic acid (AA), acetaminophenol (AP) and uric acid (UA) under physiological pH condition. The attractive analytical performances and facile preparation method made this novel hybrid electrode promising for the development of effective H?O? sensors.     

Reduced graphene oxide/PAMAM-silver nanoparticles nanocomposite modified electrode for direct electrochemistry of glucose oxidase and glucose sensing

Reduced graphene oxide/PAMAM-silver nanoparticles nanocomposite (RGO-PAMAM-Ag) was synthesized by self-assembly of carboxyl-terminated PAMAM dendrimer (PAMAM-G3.5) on graphene oxide (GO) as growing template, and in-situ reduction of both AgNO(3) and GO under microwave irradiation. The RGO-PAMAM-Ag nanocomposite was used as a novel immobilization matrix for glucose oxidase (GOD) and exhibited excellent direct electron transfer properties for GOD with the rate constant (K(s)) of 8.59 s(-1). The fabricated glucose biosensor based on GOD electrode modified with RGO-PAMAM-Ag nanocomposite displayed satisfactory analytical performance including high sensitivity (75.72 μA mM(-1) cm(-2)), low detection limit (4.5 μM), an acceptable linear range from 0.032 mM to 1.89 mM, and also preventing the interference of some interfering species usually coexisting with glucose in human blood at the work potential of -0.25 V. These results indicated that RGO-PAMAM-Ag nanocomposite is a promising candidate material for high-performance glucose biosensors.     

Immobilization of creatininase, creatinase and sarcosine oxidase on iron oxide nanoparticles/chitosan-g-polyaniline modified Pt electrode for detection of creatinine

Commercial enzymes, creatininase (CA) from Pseudomonas sp, creatinase (CI) from Pseudomonas sp, sarcosine oxidase (SO) from Bacillus sp were co-immobilized onto iron oxide nanoparticles/chitosan-graft-polyaniline (Fe(3)O(4)-NPs/CHIT-g-PANI) composite film electrodeposited on surface of Pt electrode through glutaraldehyde coupling. Transmission electron microscopy (TEM) was used for characterization of Fe(3)O(4)-NPs. A creatinine biosensor was fabricated using Enzymes/Fe(3)O(4)-NPs/CHIT-g-PANI/Pt electrode as working electrode, Ag/AgCl as reference electrode and Pt wire as auxiliary electrode. The enzyme electrode was characterized by cyclic voltammetry (CV), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopic and electrochemical impedance spectroscopy (EIS). The biosensor exhibited an optimum response within 2s at pH 7.5 and 30 °C, when polarized at 0.4V vs Ag/AgCl. The electrocatalytic response showed a linear dependence on creatinine concentration ranging from 1 to 800 μM. The sensitivity of the biosensor was 3.9 μA μM(-1) cm(-2), with a detection limit of 1 μM (S/N=3). Apparent Michaelis-Menton (K(m)) value for creatinine was 0.17 mM. The biosensor showed only 10% loss in its initial response after 120 uses over 200 days, when stored at 4 °C. The biosensor measured creatinine in the serum of apparently healthy persons which correlated well with a standard colorimetric method (r=0.99).     

Palladium nanoparticle/chitosan-grafted graphene nanocomposites for construction of a glucose biosensor

Graphene (GR) was covalently functionalized with chitosan (CS) to improve its biocompatibility and hydrophilicity for the preparation of biosensors. The CS-grafted GR (CS-GR) rendered water-soluble nanocomposites that were readily decorated with palladium nanoparticles (PdNPs) using in situ reduction. Results with TEM, SEM, FTIR, Raman and XRD revealed that CS was successfully grafted without destroying the structure of GR, and PdNPs were densely decorated on CS-GR sheets with no aggregation occurring. A novel glucose biosensor was then developed through covalently immobilizing glucose oxidase (GOD) on a glassy carbon electrode modified with the PdNPs/CS-GR nanocomposite film. Due to synergistic effect of PdNPs and GR, the PdNPs/CS-GR nanocomposite film exhibited excellent electrocatalytical activity toward H(2)O(2) and facilitated high loading of enzymes. The biosensor demonstrated high sensitivity of 31.2 μA mM(-1)cm(-2) for glucose with a wide linear range from 1.0 μM to 1.0mM as well as a low detection limit of 0.2 μM (S/N=3). The low Michaelis-Menten constant (1.2mM) suggested enhanced enzyme affinity to glucose. These results indicated that PdNPs/CS-GR nanocomposites held great potential for construction of a variety of electrochemical biosensors.     

Novel snowflake-like Pt-Pd bimetallic clusters on screen-printed gold nanofilm electrode for H2O2 and glucose sensing

Novel snowflake-like Pt-Pd bimetallic nanoclusters (Pt-PdBNC) were synthesized on a screen-printed gold nanofilm electrode (SPGFE) substrate by electrochemically reducing precursors with a new constant potential/multi-potential step deposition strategy. The electrocatalytic behavior of the modified electrode (SPGFE/Pt-PdBNC) towards H(2)O(2) was investigated. The results indicate that the as-prepared Pt-PdBNC significantly enhances the electrochemical reduction of H(2)O(2) in neutral media, exhibiting preferable electrocatalytic performance compared to Pt and Pd monometallic nanoclusters. Under optimum conditions, SPGFE/Pt-PdBNC offers linear responses for H(2)O(2) in the concentration range from 0.005 to 6 mM with an ultrahigh sensitivity of 804 mA M(-1) cm(-2) and excellent selectivity. Furthermore, glucose oxidase was immobilized on the Pt-PdBNC structure, and the fabricated biosensor presents favorable properties for glucose sensing.     

Low potential detection of NADH based on Fe₃O₄ nanoparticles/multiwalled carbon nanotubes composite: fabrication of integrated dehydrogenase-based lactate biosensor

Fe(3)O(4) magnetic nanoparticles were in situ loaded on the surface of multiwalled carbon nanotubes (MWCNTs) by a simple coprecipitation procedure. The resulting Fe(3)O(4)/MWCNTs nanocomposite brings new capabilities for electrochemical sensing by combining the advantages of Fe(3)O(4) magnetic nanoparticles and MWCNTs. It was found that Fe(3)O(4) has redox properties similar to those of frequently used mediators used for electron transfer between NADH and electrode. The cyclic voltammetric results indicated the ability of Fe(3)O(4)/MWCNTs modified GC electrode to catalyze the oxidation of NADH at a very low potential (0.0 mV vs. Ag/AgCl) and subsequently, a substantial decrease in the overpotential by about 650 mV compared with the bare GC electrode. The catalytic oxidation current allows the stable and selective amperometric detection of NADH at an applied potential of 0.0 mV (Ag/AgCl) with a detection limit of 0.3 μM and linear response up to 300 μM. This modified electrode can be used as an efficient transducer in the design of biosensors based on coupled dehydrogenase enzymes. Lactate dehydrogenase (LDH) and NAD(+) were subsequently immobilized onto the Fe(3)O(4)/MWCNTs nanocomposite film by covalent bond formation between the amine groups of enzyme or NAD(+) and the carboxylic acid groups of the Fe(3)O(4)/MWCNT film. Differential pulse voltammetric detection of lactate on Fe(3)O(4)/MWCNT/LDH/NAD(+) modified GC electrode gives linear responses over the concentration range of 50-500 μM with the detection limit of 5 μM and sensitivity of 7.67 μA mM(-1). Furthermore, the applicability of the sensor for the analysis of lactate concentration in human serum samples has been successfully demonstrated.     

High-performance bioanode based on the composite of CNTs-immobilized mediator and silk film-immobilized glucose oxidase for glucose/O2 biofuel cells

A high-performance bioanode based on the composite of carbon nanotubes (CNTs)-immobilized mediator and silk film (SF)-immobilized glucose oxidase (GOD) was developed for glucose/O(2) biofuel cell (BFC). Ferrocenecarboxaldehyde (Fc) was used as the mediator and covalently immobilized on the ethylenediamine (EDA)-functionalized CNTs (CNTs-EDA). GOD was cross-linked on the SF with glutaraldehyde (GA) as the cross-linking agent. The resulting electrode (CNTs-Fc/SF-GOD/glassy carbon (GC) electrode) exhibited good catalytic activity towards glucose oxidation and excellent stability. For the assembled glucose/O(2) BFC with the CNTs-Fc/SF-GOD/GC electrode as the bioanode and a commercial E-TEK Pt/C modified GC electrode as the cathode, the open circuit potential is 0.48 V and the maximum power density of 50.70 μW cm(-2) can be achieved at 0.15 V.     

A novel hydrogen peroxide biosensor based on the immobilization of hemoglobin on three-dimensionally ordered macroporous (3DOM) gold-nanoparticle-doped titanium dioxide (GTD) film

The three-dimensionally ordered macroporous gold-nanoparticle-doped titanium dioxide (3DOM GTD) film was modified on the indium-tin oxide (ITO) electrode surface. Hemoglobin (Hb) has been successfully immobilized on the 3DOM GTD film and the fabrication process was characterized by Raman and UV-vis spectra. The results indicated that the Hb immobilized on the film retained its biological activity and the secondary structure of Hb was not destroyed. The direct electrochemistry and electrocatalysis of Hb immobilized on this film have been investigated. The Hb/3DOM GTD/ITO electrode exhibited two couples of redox peaks corresponding to the Hb intercalated in the mesopores and adsorbed on the external surface of the film with the formal potential of -0.20 and -0.48 V in 0.1M PBS (pH7.0), respectively. The Hb/3DOM GTD/ITO electrode exhibits an excellent eletrocatalytic activity, a wide linear range for H(2)O(2) from 5.0 μM to 1.0mM with a limit of detection of 0.6μM, high sensitivity (144.5 μA mM(-1)), good stability and reproducibility. Compared with the TiO(2) nanoneedles modified electrode, the GTD modified electrode has higher sensitivity and response peak current. The 3DOM GTD provided a good matrix for bioactive molecules immobilization, suggesting it has the potential use in the fields of H(2)O(2) biosensors.     

Simultaneous detection of NADH and H₂O₂ using flow injection analysis based on a bifunctional poly(thionine)-modified electrode

We report here a novel detection scheme for simultaneous detection of NADH and H(2)O(2) based on a bifunctional poly(thionine)-modified electrode. Electropolymerization of thionine on a "preanodized" screen-printed carbon electrode effectively lowers the oxidation potential of NADH to 0.15 V (vs. Ag/AgCl). Since poly(thionine) is also a well known electrochemical mediator for H(2)O(2) reduction, we further developed a poly(thionine)-modified ring disk electrode for simultaneous measurement of nicotinamide adenine dinucleotide (NADH) and hydrogen peroxide (H(2)O(2)) by flow injection analysis. By applying the optimized detection potentials of 0.2V and -0.2V at disk and ring electrodes, respectively, this system allows the simultaneous measurement of both analytes with good sensitivity (0.13 μA/mM for H(2)O(2) and 0.34 μA/mM for NADH) and limit of detection (1.74 μM and 26.0 μM for NADH and H(2)O(2)). This opens the possibility of a whole series of biosensor applications.     

DNA electrochemical biosensor based on thionine-graphene nanocomposite

A novel protocol for development of DNA electrochemical biosensor based on thionine-graphene nanocomposite modified gold electrode was presented. The thionine-graphene nanocomposite layer with highly conductive property was characterized by scanning electron microscopy, transmission electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. An amino-substituted oligonucleotide probe was covalently grafted onto the surface of the thionine-graphene nanocomposite by the cross-linker glutaraldehyde. The hybridization reaction on the modified electrode was monitored by differential pulse voltammetry analysis using an electroactive intercalator daunomycin as the indicator. Under optimum conditions, the proposed biosensor exhibited high sensitivity and low detection limit for detecting complementary oligonucleotide. The complementary oligonucleotide could be quantified in a wide range of 1.0 × 10(-12) to 1.0 × 10(-7)M with a good linearity (R(2)=0.9976) and a low detection limit of 1.26 × 10(-13)M (S/N=3). In addition, the biosensor was highly selective to discriminate one-base or two-base mismatched sequences.     

Low-potential sensitive H2O2 detection based on composite micro tubular Te adsorbed on platinum electrode

In this work a new original amperometric sensor for H(2)O(2) detection based on a Pt electrode modified with Te-microtubes was developed. Te-microtubes, synthesized by the simple thermal evaporation of Te powder, have a tubular structure with a hexagonal cross-section and are open ended. Modified electrode was prepared by direct drop casting of the mixture of Te-microtubes dispersed in ethanol on Pt surface. The spectroscopic characterization of synthesized Te-microtubes and Pt/Te-microtubes modified electrodes was performed by scanning electron microscopy (SEM), energy-dispersive X-rays microanalysis (EDX), X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscopy (XPS). Moreover a complete electrochemical characterization of the new composite material Pt/Te-microtubes was performed by cyclic voltammetry (CV) and cronoamperometry (CA) in phosphate buffer solution (PBS) at pH 7. Electrochemical experiments showed that the presence of Te-microtubes on modified electrode was responsible for an increment of both cathodic and anodic currents in presence of H(2)O(2) with respect to bare Pt. Specifically, data collected from amperometric experiments at -150 mV vs. SCE in batch and -200 mV vs. SCE in flow injection analysis (FIA) experiments show a remarkable increment of the cathodic current. The electrochemical performances of tested sensors make them suitable for the quantitative determination of H(2)O(2) substrate both in batch and in FIA.     

Sensitive detection of endonuclease activity and inhibition using gold nanorods

A sulfite oxidase (SO(X)) (EC 1.8.3.1) purified from Syzygium cumini leaves was immobilized onto carboxylated gold coated magnetic nanoparticles (Fe(3)O(4)@GNPs) electrodeposited onto the surface of a gold (Au) electrode through N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide (EDC)-N-hydroxy succinimide (NHS) chemistry. An amperometric sulfite biosensor was fabricated using SO(X)/Fe(3)O(4)@GNPs/Au electrode as working electrode, Ag/AgCl as standard and Pt wire as auxiliary electrode. The working electrode was characterized by Fourier Transform Infrared (FTIR) Spectroscopy, Cyclic Voltammetry (CV), Scanning Electron Microscopy (SEM) and Electrochemical Impedance Spectroscopy (EIS) before and after immobilization of SO(X). The biosensor showed optimum response within 2s when operated at 0.2V (vs. Ag/AgCl) in 0.1 M Tris-HCl buffer, pH 8.5 and at 35 °C. Linear range and detection limit were 0.50-1000 μM and 0.15 μM (S/N=3) respectively. Biosensor was evaluated with 96.46% recovery of added sulfite in red wine and 1.7% and 3.3% within and between batch coefficients of variation respectively. Biosensor measured sulfite level in red and white wines. There was good correlation (r=0.99) between red wines sulfite value by standard DTNB (5,5'-dithio-bis-(2-nitrobenzoic acid)) method and the present method. Enzyme electrode was used 300 times over a period of 4 months, when stored at 4 °C. Biosensor has advantages over earlier biosensors that it has excellent electrocatalysis towards sulfite, lower detection limit, higher storage stability and no interference by ascorbate, cysteine, fructose and ethanol.     

A novel approach to construct a horseradish peroxidase|hydrophilic ionic liquids|Au nanoparticles dotted titanate nanotubes biosensor for amperometric sensing of hydrogen peroxide

The direct electrochemistry of horseradish peroxidase (HRP) on a novel sensing platform modified glassy carbon electrode (GCE) has been achieved. This sensing platform consists of Nafion, hydrophilic room-temperature ionic liquid (RTIL) and Au nanoparticles dotted titanate nanotubes (GNPs-TNTs). The composite of RTIL and GNPs-TNTs was immobilized on the electrode surface through the gelation of a small amount of HRP aqueous solution. The composite was characterized by transmission electron microscopy (TEM), powder X-ray diffraction (XRD) and infrared spectroscopy (IR). UV-Vis and IR spectroscopy demonstrated that HRP in the composite could retain its native secondary structure and biochemical activity. The HRP-immobilized electrode was investigated by cyclic voltammetry and chronoamperometry. The results from both techniques showed that the direct electron transfer between the nanocomposite modified electrodes and heme in HRP could be realized. The biosensor responded to H(2)O(2) in the linear range from 5×10(-6) to 1×10(-3) mol L(-1) with a detection limit of 2.1×10(-6) mol L(-1) (based on the S/N=3).     

Immobilization of lutetium bisphthalocyanine in nanostructured biomimetic sensors using the LbL technique for phenol detection

This study describes the development of amperometric sensors based on poly(allylamine hydrochloride) (PAH) and lutetium bisphthalocyanine (LuPc(2)) films assembled using the Layer-by-Layer (LbL) technique. The films have been used as modified electrodes for catechol quantification. Electrochemical measurements have been employed to investigate the catalytic properties of the LuPc(2) immobilized in the LbL films. By chronoamperometry, the sensors present excellent sensitivity (20 nA μM(-1)) in a wide linear range (R(2)=0.994) up to 900 μM and limit of detection (s/n=3) of 37.5 × 10(-8)M for catechol. The sensors have good reproducibility and can be used at least for ten times. The work potential is +0.3 V vs. saturated calomel electrode (SCE). In voltammetry measurements, the calibration curve shows a good linearity (R(2)=0.992) in the range of catechol up to 500 μM with a sensitivity of 90 nA μM(-1) and LD of 8 μM.     

Electrophoretic transfer protein zymography

A mixture of commercial creatinine amidohydrolase (CA), creatine amidinohydrolase (CI), and sarcosine oxidase (SO) was coimmobilized covalently via N-ethyl-N′-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxy succinimide (NHS) chemistry onto carboxylated multiwalled carbon nanotube (c-MWCNT)/polyaniline (PANI) nanocomposite film electrodeposited over the surface of a platinum (Pt) electrode. A creatinine biosensor was fabricated using enzyme/c-MWCNT/PANI/Pt as working electrode, Ag/AgCl as reference electrode, and Pt wire as auxiliary electrode connected through potentiostat. The enzyme electrode was characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and electrochemical impedance spectroscopy (EIS). The biosensor detected creatinine levels as low as 0.1 μM, estimated at a signal-to-noise ratio of 3, within 5 s at pH 7.5 and 35 °C. The optimized biosensor showed a linear response range of 10 to 750 μM creatinine with sensitivity of 40 μA/mM/cm². The fabricated biosensor was successfully employed for determination of creatinine in human serum. The biosensor showed only 15% loss in its initial response after 180 days when stored at 4 °C.     

Nanostructured electrode based on multi-wall carbon nanotubes/Pt microparticles nanocomposite for electrochemical determination of thiols in rat striatum by high performance liquid chromatography separation

In this paper, multi-wall carbon nanotubes (MWNTs)/Pt microparticles nanocomposite was prepared by electrodepositing Pt microparticles onto the MWNTs matrix. The surface of glassy carbon electrode was modified with this kind of nanocomposite for measurement of thiols, such as L-cysteine (L-Cys) and glutathione (GSH). Compared with the MWNTs or Pt microparticles modified electrode, the nanocomposite modified electrode exhibited high sensitivity and good stability for detection of thiols. According to the results of experiments, the peak currents of L-Cys and GSH are linear with their concentrations and the detection limits (S/N=3) are 2.9 x 10(-8) mol/L and 4.5 x 10(-8) mol/L, respectively. Coupled with microdialysis, the method has been successfully applied to the determination of these two thiols in rat striatal microdialysates.     

Surface renewable sol-gel composite electrode derived from 3-aminopropyl trimethoxy silane with covalently immobilized thionin

Sol-gel technique has been used for the covalent immobilization of the water-soluble mediator, thionin to construct a bulk modified, leak free composite electrode. This renewable composite electrode provides stable immobilization matrix for thionin via glutaraldehyde crosslinking. In the electrode composition the sol-gel precursor 3-aminopropyltrimethoxy silane serves as the host for immobilization of thionin, thereby preventing its leakage. An additional precursor methyl trimethoxy silane endows hydrophobicity and limits the wetting section of the modified electrode. Cyclic voltammetric characterization of the modified electrode in the potential range of 0.2 to -0.6 V exhibited stable redox peaks with a formal potential of -0.273 V, corresponding to immobilized thionin. This chemically modified electrode exhibits good electrocatalytic activity for the reduction of H(2)O(2) at a lower potential of -0.35 V. The reduction current of the modified electrode increases linearly in the range of 3.44 x 10(-6)M to 3.07 x 10(-3)M H(2)O(2) with a detection limit of 1.38 x 10(-6)M. The stable and quick response (5s) during chronoamperometry shows the potential application of the modified electrode for flow system analysis. The low potential operation (-0.35 V) favoured selective determination of H(2)O(2). The composite electrode exhibits distinct advantages of polishing in the event of surface fouling as well as simple preparation, good chemical and mechanical stability, economical and remarkable long-term stability (more than 1 year). The applicability of the present sensor for H(2)O(2) determination proposes a method for the detection of other biologically significant analytes.