A Reagentless Hydrogen Peroxide Biosensor Based on the Coimmobilization of Thionine and Horseradish Peroxidase by Their Cross-Linking with Glutaraldehyde on Glassy Carbon Electrode

Reagentless biosensor based on layer-by-layer assembly of functional multiwall carbon nanotubes and enzyme-mediator biocomposite

A simple and controllable layer-by-layer (LBL) assembly method was proposed for the construction of reagentless biosensors based on electrostatic interaction between functional multiwall carbon nanotubes (MWNTs) and enzyme-mediator biocomposites. The carboxylated MWNTs were wrapped with polycations poly(allylamine hydrochloride) (PAH) and the resulting PAH-MWNTs were well dispersed and positively charged. As a water-soluble dye methylene blue (MB) could mix well with horseradish peroxidase (HRP) to form a biocompatible and negatively-charged HRP-MB biocomposite. A (PAH-MWNTs/HRP-MB)(n) bionanomultilayer was then prepared by electrostatic LBL assembly of PAH-MWNTs and HRP-MB on a polyelectrolyte precursor film-modified Au electrode. Due to the excellent biocompatibility of HRP-MB biocomposite and the uniform LBL assembly, the immobilized HRP could retain its natural bioactivity and MB could efficiently shuttle electrons between HRP and the electrode. The incorporation of MWNTs in the bionanomultilayer enhanced the surface coverage concentration of the electroactive enzyme and increased the catalytic current response of the electrode. The proposed biosensor displayed a fast response (2 s) to hydrogen peroxide with a low detection limit of 2.0×10⁻⁷ mol/L (S/N=3). This work provided a versatile platform in the further development of reagentless biosensors.

A selective novel non-enzyme glucose amperometric biosensor based on lectin-sugar binding on thionine modified electrode

A novel non-enzyme glucose amperometric biosensor was fabricated based on biospecific binding affinity of concanavalin A (Con A) for D-glucose on thionine (TH) modified electrode. TH can be covalently immobilized on potentiostatically activated glassy carbon electrode through Schiff-base reaction. Subsequently, the surface-adherent polydopamine film formed by self-polymerization of dopamine attached to TH and afforded binding sites for the subsequent immobilization of Con A molecules via Michael addition and/or Schiff-base reaction with high stability. Thus, a sensing platform for specific detection towards D-glucose was established. The binding of Con A towards D-glucose can be monitored through the decrease of the electrode response of the TH moiety. Due to the high affinity of Con A for D-glucose and high stability of the resulting sensing platform, the fabricated biosensor exhibited high selectivity, good sensitivity, and wide linear range from 1.0×10(-6) to 1.0×10(-4) M with a low detection limit of 7.5×10(-7) M towards D-glucose.

A novel protocol for covalent immobilization of thionine on glassy carbon electrode and its application in hydrogen peroxide biosensor

A novel protocol for effectively covalent immobilization of thionine (Th) was proposed, which was based on Schiff-base reaction between -NH(2) of Th and -COH which was in situ generated on glassy carbon electrode (GCE) via simple potentiostatic activation in diluted nitric acid. GCE pretreated by potentiostatic activation possessed CHO-riched surface and microporous structure with high distribution density of electron transfer sites, and thus it became a good candidate for effective immobilization of Th through imine bond with high stability. The application of the resulting Th modified electrode in hydrogen peroxide biosensor was also investigated and it exhibited rapid response to H(2)O(2) within 3s. The linear calibration ranged from 5.0x10(-7) to 5.8x10(-3)M with a detection limit of 1.0x10(-7)M. The effective immobilization of Th on potentiostatically activated GCE surface has deep significance in mediator immobilization, on which further researches based are under way.

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.

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.

Screen-printed biosensors for glucose determination in grape juice

An approach to the glucose determination by amperometric biosensing in wine industry applications is presented. Integrated screen-printed biosensors based on horseradish peroxidase (HRP) and glucose oxidase (GOx) have been developed. The experimental design methodology has been used to find the optimum conditions of the experimental variables, in such a way that a chronoamperometric response specific for glucose was recorded. Under these conditions, repeatability and reproducibility of the modified electrodes have been analyzed. The detection limit for glucose has been calculated taking into account the probability of false positive (alpha) and negative (beta), reaching a medium value of 4.37+/-0.21 micromol dm-3 (alpha=beta=0.05, and a replicate n=4). The biosensor was applied to the determination of glucose in white wine samples.

Carbon Felt-based Bioelectrocatalytic Flow Detectors: Highly Sensitive Amperometric Determination of Hydrogen Peroxide Using Adsorbed Peroxidase and Thionine

Horseradish peroxidase (HRP) and thionine (TN) were co-adsorbed onto a porous carbon felt (CF), and the resulting HRP and TN-adsorbed CF (HRP-TN-CF) was successfully used as a working electrode unit of a novel bioelectrocatalytic flow detector for a highly sensitive amperometric determination of hydrogen peroxide (H(2)O(2)). Co-adsorbed TN was essential to enhance the cathodic peak current of H(2)O(2), and the current responses of the HRP-TN-CF-based detector were much larger than those of the HRP-CF-based detector (without TN). When air-saturated 0.1 M phosphate buffer (pH 7.0) was used as a carrier at a flow rate of 3.9 ml/min, cathodic peak currents of H(2)O(2) (sample injection volume, 200 microl) obtained at an applied potential of 0 V (vs. Ag/AgCl) increased linearly up to 50 microM with a detection limit of 0.1 microM. Repetitive 100 sample injection of 100 microM H(2)O(2) induced no serious current decrease, and RSD was 0.41 to 1.21% (n = 100). The HRP-TN-CF retained 42% of its original activity after 8 days of storage in 0.1 M phosphate buffer at 4 degrees C.

Degradation of 2,4,6-trinitrotoluene by immobilized horseradish peroxidase and electrogenerated peroxide

This paper presents horseradish peroxidase (HRP)-catalyzed removal of 2,4,6-trinitrotoluene (TNT) by an electrochemical packed-bed flow reactor operated in a circulating batch mode with the help of in situ generated hydrogen peroxide. HRP immobilized on the reticulated vitreous carbon electrode was prepared for the cyclic voltammetry of 2,4,6-TNT. Effects of pH and temperature on the TNT electroreduction in 0.2M phosphate buffer saturated with oxygen were examined. HRP immobilized carbon electrode was capable of catalyzing the oxidation and detoxification of 44 microM TNT in aqueous solution under optimized conditions. The removal rate of TNT for the electroenzymatic method was much greater than for electrochemical and biochemical methods. Stoichiometric and kinetic studies indicated that the hydrogen peroxide was utilized more effectively in the electroenzymatic method. Denitrification as intermediate reaction was also investigated.

Mediated electrochemical detection of catechol by tyrosinase-based poly(dicarbazole) electrodes

A new dicarbazole derivative functionalised by an N-hydroxysuccinimide group has been synthesised and electrochemically characterised. Upon oxidative electropolymerisation of this monomer in organic electrolytes, electroactive poly(dicarbazole) films were formed on platinum electrodes. The subsequent chemical grafting of tyrosinase on the poly(dicarbazole) film was easily performed by immersion in an enzymatic aqueous solution. The amperometric response of the resulting biosensors to catechol has been studied at -0.2 V vs. saturated calomel electrode (SCE). Since the reduction of quinone generates radicals which may induce electrode fouling, thionine, a phenothiazine dye, was covalently bound to the poly(dicarbazole) backbone as it mediates the reduction of quinoid products and therefore induces an enhancement of the performance of the tyrosinase-based biosensor.