Glucose microsensor based on electrochemical deposition of iridium and glucose oxidase onto carbon fiber electrodes

Doble role of bathocuproine disulfonic acid as multi-walled carbon nanotubes dispersing agent and copper preconcentration ligand: Analytical applications for the development of hydrogen peroxide and glucose electrochemical sensors

We are reporting a new strategy for preparing carbon nanotubes (CNTs)-based hydrogen peroxide and glucose amperometric sensors by taking advantage of the dual role of bathocuproine disulfonic acid (BCS) as dispersing agent of multi-walled carbon nanotubes (MWCNTs) and as ligand for the preconcentration of Cu(II). The platform was obtained by casting glassy carbon electrodes (GCE) with the dispersion of MWCNTs in BCS (MWCNTs-BCS) followed by the preconcentration of Cu(II) by surface complex formation at open circuit potential (GCE/MWCNTs-BCS/Cu). The resulting electrode was used for the sensitive amperometric quantification of hydrogen peroxide at 0.400 V catalyzed by the preconcentrated copper, with a linear range between 5.0 × 10^-7 and 7.4 × 10^-6 M, a sensitivity of 24.3 mA.M^-1, and a detection limit of 0.2 μM. The adsorption of GOx at GCE/MWCNTs-BCS/Cu followed by the immobilization of Nafion (Naf), allowed the construction of a sensitive and selective amperometric glucose biosensor with a linear range between 5.0 × 10^-6 M and 4.9 × 10^-4 M, a sensitivity of (477 ± 3) μA.M^-1 and a detection limit of 2 μM. The proposed (bio)sensors were successfully used for the quantification of hydrogen peroxide in enriched milk samples and glucose in milk and commercial beverages without any pretreatment.

Nanomolar detection of hydrogen peroxide on glassy carbon electrode modified with electrodeposited cobalt oxide nanoparticles

The electrochemical detection of H2O2 was investigated on a cobalt oxide nanoparticles modified glassy carbon electrode in phosphate buffer solution (pH 7). Cyclic voltammetry at potential range -1.1 to 1.1 V from CoCl2 natural aqueous solution produced well defined cobalt oxide nanoparticles deposited on the surface of glassy carbon electrode. The surface of resulting electrode was characterized with SEM. The formation of cobalt oxyhydroxide film was investigated by cyclic voltammetry in alkaline and natural aqueous solution. The modified electrode showed well defined and stable redox couples in both alkaline and natural aqueous solution. The modified electrode showed excellent electrocatalytic activity for oxidation of hydrogen peroxide. The response to H2O2 on the modified electrode was examined using cyclic voltammetry and amperometry. The amperometric detection of hydrogen peroxide is carried out at 0.75 V versus Ag/AgCl reference electrode in phosphate buffer solution with pH 7.4. The detection limit (S/N=3) was 0.4 nM with linearity up to 6 orders of magnitude and sensitivity of 4.86 microA microM(-1) cm(-2). The response time of the electrode to achieve 95% of the steady-state current is <2 s. No measurable reduction in analytical performance of the modified electrode was found by storing the electrode in ambient conditions for 20 days. This modified electrode recedes many advantages such as remarkable catalytic activity, good reproducibility, simple preparation procedure and long term stability of signal response during hydrogen peroxide oxidation. The immobilization of cobalt oxide nanoparticles on the surface of GC electrode appears to be a highly efficient method for the development of a new class of sensitive, stable and reproducible hydrogen peroxide electrochemical sensor.

An amperometric uric acid biosensor based on modified Ir–C electrode

The level of uric acid (UA) has a high relationship with gout, hyperuricemia and Lesch-Nyan syndrome. The determination of UA is an important indicator for clinics and diagnoses of kidney failure. An amperometric UA biosensor based on an Ir-modified carbon (Ir-C) working electrode with immobilizing uricase (EC 1.7.3.3) was developed by thick film screen printing technique. This is the first time to report the utilization of an uricase/Ir-C electrode for the determination of UA by using chronoamperometric (CA) method. The high selectivity of UA biosensor was achieved due to the reduction of H(2)O(2) oxidation potential based on Ir-C electrode. Using uricase/Ir-C as the sensing electrode, the interference from the electroactive biological species, such as ascorbic acid (AA) and UA (might be directly oxidized on the sensing electrode) was slight at the sensing potential of 0.25 V (versus Ag/AgCl). UA was detected amperometrically based on uricase/Ir-C electrode with a sensitivity of 16.60 microAmM(-1) over the concentration range of 0.1-0.8 mMUA, which was within the normal range in blood. The detection limit of UA biosensor was 0.01 mM (S/N=6.18) in pH 7 phosphate buffer solution (PBS) at 37 degrees C. The effects of pH, temperature, and enzymatic loading on the sensing characteristics of the UA biosensor were also investigated in this study.

Controlling the electrochemically active area of carbon fiber microelectrodes by the electrodeposition and selective removal of an insulating photoresist

A new and simple method permits control of the electrochemically active area of a carbon fiber microelectrode. An electrophoretic photoresist insulates the 10-microm-diameter carbon fiber microelectrodes. Photolysis of the photoresist followed by immersion of the exposed area into a developing solution reveals electroactive carbon fiber surface. The electroactive surface area exposed can be controlled with a good degree of reproducibility.

Highly selective microbiosensors for in vivo measurement of glucose, lactate and glutamate

An alternative approach to production of amperometric microbiosensors, which combines electrochemical electrometallization and electropolymerisation of phenylene diamine film with covalent binding enzymes, is presented. In this respect, for a sensitive detection of hydrogen peroxide (HP) at +0.4V versus Ag/AgCl (detection limit of 0.5 microM, s/n=3), carbon fiber microelectrodes (30 microm in diameter and 500 microm long) were covered with ruthenium. To obtain a highly selective detection of HP, in the presence of different interfering compounds (ascorbic acid, uric acid, etc.), an additive semi-permeable polymer film was formed on the top of the ruthenium layer by electropolymerisation of m-phenylene diamine (m-PD). The enzymatic selective layers were formed by covalent cross-linking the enzymes (glucose oxidase, lactate oxidase or glutamate oxidase) with BSA by glutaraldehyde in the presence of ascorbate oxidase. An additional polymeric layer based on polyurethane and Nafion was deposited on the top of the enzymatic membrane (glucose oxidase, lactate oxidase, or glutamate oxidase) in order to extend the dynamic range of biosensors up to 4mM for glucose (R=0.997; Y[nA]=-0.22+9.68x[glucose, mM]), 1.75mM for lactate (R=0.991; Y[nA]=0.43+15.36x[lactate, mM]) and 0.25 mM for glutamate (R=0.999; Y[nA]=0.02+29.14x[glutamate, mM]). The developed microbiosensors exhibited also negligible influences from interfering compounds at their physiological concentrations. Microbiosensors remained stable during 10h in a flow injection system at 36 degrees C and pH 7.4. The microbiosensors developed are now used in vivo and, as an example, we report here the data obtained with the glucose biosensor.

Combinatorial discovery of alloy electrocatalysts for amperometric glucose sensors

Combinatorial methods were used to search for active alloy electrocatalysts for use in enzyme-free amperometric glucose sensors. Electrode arrays (715-member) containing combinations of Pt, Pb, Au, Pd, and Rh were prepared and screened by converting anodic current to visible fluorescence. The most active compositions contained both Pt and Pb. Bulk quantities of catalysts with compositions corresponding to those identified in the screening experiments were prepared and characterized. The best alloy electrocatalysts catalyzed glucose oxidation at substantially more negative potentials than pure platinum in enzyme-free voltammetric measurements. They were also insensitive to potential interfering agents (ascorbic and uric acids, and 4-acetamidophenol), which are oxidized at slightly more positive potentials. Rotating disk electrode (RDE) experiments were carried out to study the catalytic mechanism. The improvement in catalytic performance was attributed to the inhibition of adsorption of oxidation products, which poison Pt electrodes.