The effect of organic solvent properties on the response of a tyrosinase enzyme sensor

Bioethanol in Biofuels Checked by an Amperometric Organic Phase Enzyme Electrode (OPEE) Working in "Substrate Antagonism" Format

The bioethanol content of two samples of biofuels was determined directly, after simple dilution in decane, by means of an amperometric catalase enzyme biosensor working in the organic phase, based on substrate antagonisms format. The results were good from the point of view of accuracy, and satisfactory for what concerns the recovery test by the standard addition method. Limit of detection (LOD) was on the order of 2.5 × 10(-5) M.

An electrochemical biosensing platform based on 1-formylpyrene functionalized reduced graphene oxide for sensitive determination of phenol

A novel electrochemical biosensing platform is proposed. New tyrosinase-based biosensor can be used to detect phenols.

(Bio)Sensor Approach in the Evaluation of Polyphenols in Vegetal Matrices

Polyphenols are compounds widely distributed in the plant kingdom and have attracted much attention, because of their health benefits and important properties such as radical scavenging, metal chelating agents, inhibitors of lipoprotein oxidation, anti-inflammatory and anti-allergic activities. Due to their important role in the diet and in therapy, it is important to estimate their content in the different matrices of interest. Besides classical analytical methods, new emerging technologies have also appeared in the last decade aiming for simple and eventually cheap detection of polyphenols. This review focused on the recent applications of biosensing-based technologies for polyphenol estimation in vegetal matrices, using different transduction principles. These analytical tools are generally fast, giving responses in the order of a few seconds/minutes, and also very sensitive and generally selective (mainly depending on the enzyme used). Direct measurements in most of the investigated matrices were possible, both in aqueous and organic phases.

New investigation of the isothermal oxidation of extra virgin olive oil: determination of free radicals, total polyphenols, total antioxidant capacity, and kinetic data

As a follow-up of the research programs carried out by our group concerning the artificial isothermal rancidification process in extra virgin olive oil (EVOO), in the present work the trends of both the total antioxidant capacity and the total polyphenols concentration as well as the main kinetic parameters of the process during the thermal oxidation of EVOO were studied and compared. In addition, the possibility of evaluating the increase in radicals concentration during the thermal oxidation process using a superoxide dismutase biosensor was also studied. The present investigation concerning this important food product is highly topical as it refers to the state of alteration of the EVOO used for cooking or frying, as a function of the temperature reached.

On-line monitoring of methanol in n-hexane by an organic-phase alcohol biosensor

An organic-phase alcohol biosensor has been developed by co-entrapping alcohol oxidase and horseradish peroxidase within an ionotropy polymer hydrogel matrix fabricated from silica gel particles, hydroxyethyl carboxymethylcellulose, an adduct of 3-methoxy-4-ethoxybenzaldehyde and 4-tert-butylpyridinium acetohydrazone, and octadecylsilica particles. The viability of the immobilised enzymes for the biocatalytic reaction of methanol in n-hexane was comparatively studied by using a bulk cell or a volume-changeable flow-through cell coupled with an oxygen optical transducer. It was found that the microenvironment around the enzyme, the deterioration property of the enzyme, the substrate throughput and the mass transfer process of the reactant in the bioreactor were the crucial parameters affecting the performance of the alcohol organic-phase biosensor. Our optimal biosensor was constructed from a flow-through cell packed with small particles of immobilised enzymes and it could maintain the biocatalytic reaction at high and stable rate for on-line detection of methanol in n-hexane under flow operation mode. The biosensor had an analytical working range of 2.3-90 mM methanol in n-hexane. The response times (t95) were 4.5 and 7.5 min for 60 and 10 mM methanol, respectively. The operational lifetime of the biosensor was more than 45 assays and the shelf lifetime was longer than 2 weeks. The biosensor has been successfully applied to determine the methanol content in a commercial gasoline-methanol blend sample with good recovery.

Tyrosinase inhibition organic phase biosensor for triazinic and benzotriazinic pesticide analysis (part two)

Several triazine pesticides, such as atrazine, are much more soluble in several organic solvents, such as chloroform, than in water. Our recent research was aimed at analyzing this class of pesticides using tyrosinase OPEE (organic phase enzyme electrodes), exploiting their inhibiting action on the tyrosinase enzyme when operating in water-saturated chloroform medium. In this work we studied the response of a tyrosinase inhibition enzyme sensor to several triazinic (simazine, propazine, terbuthylazine) and benzotriazinic (azinphos-ethyl and azinphos-methyl) pesticides (LOD=0.5x10(-9) mol l(-1)). Recovery trials were also performed in vegetal matrixes (corn, barley, lentils). Lastly, the effect of the solvent (chloroform or water) on the inhibition process was investigated via Hill's equation and the diffusion of analyte from the solvent to the enzyme membrane.

Biosensors for determination of total antioxidant capacity of phytotherapeutic integrators: comparison with other spectrophotometric, fluorimetric and voltammetric methods

Enzymatic electrodes based on superoxide dismutase (SOD) biosensors, working both in aqueous and non-aqueous solutions, recently developed by the present authors, were used to experimentally evaluate the antioxidant capacity of several phytotherapeutic diet integrators. The precision of this method of analysis was found to be reasonable (R. S. D. < or = 10%). The results were also compared with those obtained using a traditional spectrophotometric method as well as a spectrofluorimetric method described in literature. Lastly, the comparison was extended to another method based on cyclic voltammetry currently being trialled by the present authors.

Biosensors for determination of total and natural antioxidant capacity of red and white wines: comparison with other spectrophotometric and fluorimetric methods

Research was carried out to experimentally evaluate the antioxidant capacity of several red and white wines using a superoxide dismutase (SOD) biosensor recently developed by the present authors. Measurements were performed by comparing the biosensor response to increasing concentration of the superoxide radical produced in solution by the xanthine/xanthine oxidase system, both in the presence and absence of the test sample.The results were compared with those of two traditional spectrophotometric methods and of a spectrofluorimetric method described in literature.Lastly, also the polyphenol, sulfite and ascorbic acid contents of the different wine samples examined were measured using a tyrosinase biosensor, a sulfite oxidase biosensor and an ascorbate oxidase biosensor, respectively.

Determination of hydrogen peroxide in disinfectant solutions using a biosensor with two antagonist enzymes

The development and characterisation of a new biosensor for hydroperoxides is described, which is obtained by combining an oxygen gas diffusion amperometric electrode and two immobilized enzymes (peroxidase and tyrosinase) working in parallel and competing for the same substrate (catechol). The response of the biosensor to several hydroperoxides was investigated (LOD=0.5.10(-4) M for hydrogen peroxide). It was experimentally found that the biosensor is able to respond also to aqueous solutions of ionic peroxides (LOD=0.2.10(-4) M for potassium peroxidisulphate). The biosensor was applied to the determination of the hydrogen peroxide content of pharmaceutical products, i.e. aqueous disinfectant solutions (RSD% < or =0.5; recoveries by standard addition method between 96.0 and 98.5%).

Determination of the antioxidant capacity of samples of different types of tea, or of beverages based on tea or other herbal products, using a superoxide dismutase biosensor

Research was performed to experimentally evaluate the antioxidant capacity of different plant products sold by herbalists (ginger, dog rose, ginseng and camomile) and of several types of tea (ordinary tea, green tea, detheinated tea, lemon and peach flavoured tea) using a superoxide dismutase (SOD) biosensor recently developed by the present authors. Measurements were carried out by comparing biosensor response to the superoxide radical produced in solution using the xanthine-xanthine oxidase system, both in the presence and absence of the antioxidant sample considered. Precision of antioxidant capacity measures for herbal products and for non diluted samples was good, generally with a R.S.D.%< or =10% and a LOD value about 0.1 for relative antioxidant capacity. Also a "pool" of polyphenols from different tea samples was measured using a tyrosinase biosensor (LOD approximately 2 microM).

Analysis of lecithin in pharmaceutical products and diet integrators using a new biosensor operating directly in non aqueous solvent

One of the first examples of a bienzymatic organic phase enzyme electrode (OPEE) is described. It was obtained using two enzymes (phospholipase D and choline oxidase), both immobilised in kappa-Carrageenan gel and, as electrochemical transducer, an amperometric gas diffusion electrode for oxygen. The response of the biosensor was recorded and its sensitivity, linearity range, response time evaluated. Lastly drugs and diet products containing lecithin were analysed using the new biosensor device working in an organic mixture.

Hydrogen peroxide determination in pharmaceutical formulations and cosmetics using a new catalase biosensor

The possibility of evaluating the content of hydrogen peroxide in several authentic matrices, such as cosmetic and pharmaceutical formulations, was studied. A new catalase biosensor fabricated using an amperometric gas-diffusion oxygen sensor as electrochemical transducer and the catalase enzyme immobilized in kappa-carrageenan gel and capable of operating in both aqueous and non aqueous solvents was developed and tested for this purpose. Creams, emulsions and disinfectant solutions were analysed. To this end, a preliminary check was needed to establish the best conditions to analyse these matrices; the choice of solvent was one of the most important points studied. The solvents considered included dioxane, water-dioxane mixtures, water saturated chloroform and aqueous solutions. The different solubility properties of the matrices analysed were taken into account.