Carole Calas-Blanchard

Amperometric biosensor based on a high resolution photopolymer deposited onto a screen-printed electrode for phenolic compounds monitoring in tea infusions

An amperometric biosensor based on laccase, from Trametes versicolor (LTV), was developed and optimized for monitoring the phenolic compounds content in tea infusions. The fungal enzyme was immobilized by entrapment within polyvinyl alcohol photopolymer PVA-AWP (azide-unit pendant water-soluble photopolymer) onto disposable graphite screen-printed electrodes (SPE). Sensitivity optimization in terms of pH, temperature and applied potential was carried out. The linear range, detection limit, operational and storage stabilities were also determined. The laccase biosensor (LTV-SPE) was calibrated for o-, m- and p-diphenol as well as caffeic acid. The highest response was found at 0.1M acetate buffer pH 4.7, though it must be added the good reproducibility and operational stability were also obtained. The useful lifetime of the biosensor is estimated to be greater than 6 months. LTV-SPE was used for the determination of the equivalent phenol content (EPC) in tea infusions by the direct addition into the electrochemical cell: the results were compared with those from the Folin-Ciocalteu spectrophotometric method. The amperometric detection exhibits some interesting advantages such as high simplicity, minimal sample preparation and shorter response time. A stable and sensitive amperometric response was obtained toward standard diphenolic compounds and herbal infusions. These biosensors are useful for easy and fast monitoring of EPC that can be related to the antioxidant capacity of natural extracts.

Development of a cytochrome c-based screen-printed biosensor for the determination of the antioxidant capacity of orange juices.

This paper describes the development of an amperometric cytochrome c (cyt c)-based biosensor and its later application to the quantification of the scavenging capacity of antioxidants. The enzymatic biosensor was constructed by covalently co-immobilizing both cyt c and XOD on a mercaptoundecanol/mercaptoundecanoic acid (MU/MUA) mixed self-assembled monolayer (SAM)-modified screen-printed gold electrode. The applicability of this method was shown by analyzing the antioxidant capacity of pure substances, such as ascorbic acid and Trolox, and natural sources of antioxidants, particularly 5 orange juices.

Textural characterisation of graphite matrices using electrochemical methods

The present work describes a novel approach for the textural characterisation of a carbonaceous porous medium. Due to the electronic conduction properties of expanded natural graphite (ENG), electrochemical determination was proposed and the use of cyclic voltammetry enables determination of the surface area and porous volume of ENG. First, experiments were performed without the electrochemical electron transfer reaction. Then, the volume of the entire transformation of potassium hexacyanoferrate into the pores of the material was deduced by applying the rules of thin-layer electrochemistry. For the specific surface area and the porosity, the results are satisfying, but in comparison with classical methods, the electrochemical procedure does not allow the determination of the pore size distribution of the material. It is possible to evaluate the mean pore diameter and to assume that the double-layer capacitance may depend on the kind of graphite surface (basal or edge plane).

Electrochemical characterization of a superoxide biosensor based on the co-immobilization of cytochrome c and XOD on SAM-modified gold electrodes and application to garlic samples

This paper describes the characterization and optimization of an amperometric cytochrome c (cyt c)-based sensor for the determination of the antioxidant capacity of pure substances and natural samples. The cyt c and the xanthine oxidase (XOD) enzyme were co-immobilized on the electrode using the combination of several long-chain thiols. The self-assembled monolayer (SAM) was optimized in terms of composition and ratio between thiols. The immobilization protocol for both cyt c and XOD and the SAM formation time were evaluated through electrochemical methods, such as cyclic voltammetry (CV), square wave voltammetry (SWV), chronoamperometry (CA) and impedance spectroscopy (IS). Finally, the biosensor was applied to the determination of the antioxidant capacity of pure alliin and two compounds extracted from garlic bulbs.

Biosensors as Analytical Tools in Food Fermentation Industry

The food industries need rapid and affordable methods to assure the quality ofproducts and process control. Biosensors, combining a biological recognition element and a sensitive transducer, are versatile analytical tools that offer advantages as classical analytical methods due to their inherent specificity, selectivity and simplicity. This paper reviews the recent trends in the development and applications of biosensors used in food fermentation industry, focusing on amperometric enzymatic and microbial sensors.

A novel amperometric biosensor for ß-triketone herbicides based on hydroxyphenylpyruvate dioxygenase inhibition: A case study for sulcotrione

An amperometric biosensor was designed for the determination of sulcotrione, a β-triketone herbicide, based on inhibition of hydroxyphenylpyruvate dioxygenase (HPPD), an enzyme allowing the oxidation of hydroxyphenylpyruvate (HPP) in homogentisic acid (HGA). HPPD was produced by cloning the hppd gene from Arabidopsis thaliana in E. coli, followed by overexpression and purification by nickel-histidine affinity. The electrochemical detection of HPPD activity was based on the electrochemical oxidation of HGA at +0.1 V vs. Ag/AgCl, using a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate-modified screen-printed electrode. Assays were performed at 25°C in 0.1 M phosphate buffer pH 8 containing 0.1M KCl. The purified HPPD was shown to display a maximum velocity of 0.51 µM(HGA) min(-1), and an apparent K(M) of 22.6 µM for HPP. HPPD inhibition assays in presence of sulcotrione confirmed a competitive inhibition of HPPD, the calculated inhibition constant K(I) was 1.11.10(-8) M. The dynamic range for sulcotrione extended from 5.10(-10) M to 5.10(-6) M and the limit of detection (LOD), estimated as the concentration inducing 20% of inhibition, was 1.4.10(-10) M.

Biosensor-based real-time monitoring of paracetamol photocatalytic degradation.

This paper presents for the first time the integration of a biosensor for the on-line, real-time monitoring of a photocatalytic degradation process. Paracetamol was used as a model molecule due to its wide use and occurrence in environmental waters. The biosensor was developed based on tyrosinase immobilization in a polyvinylalcohol photocrosslinkable polymer. It was inserted in a computer-controlled flow system installed besides a photocatalytic reactor including titanium dioxide (TiO2) as photocatalyst. It was shown that the biosensor was able to accurately monitor the paracetamol degradation with time. Compared with conventional HPLC analysis, the described device provides a real-time information on the reaction advancement, allowing a better control of the photodegradation process.

Potentialities of expanded natural graphite as a new transducer for NAD+-dependent dehydrogenase amperometric biosensors

The present work deals with the use of the porous texture of expanded natural graphite (ENG) as transducer in order to design electrochemical biosensors. The sensing element is a NAD+-dependent dehydrogenase. An electrochemical pretreatment of the ENG is favorable because it allows on one hand generating functional surface groups that may act as mediators for NADH oxidation and, on the other hand, eliminating enzyme-toxic compounds. The electrocatalytic oxidation of NADH on the pretreated material leads to the formation of enzymatically active NAD+. However, some persistent problems, mainly related to enzyme instability, still hamper the development of the biosensors.

Determination of the Antioxidants’ Ability to Scavenge Free Radicals Using Biosensors

Free radicals are highly reactive molecules generated during cellular metabolism. However, their overproduction results in oxidative stress, a deleterious process that can damage cell structures, including lipids and membranes, proteins and DNA. Antioxidants respond to this problem, scavenging free radicals. This chapter critically reviews the electrochemical biosensors developed for the evaluation of the antioxidant capacity of specific compounds. Due to the ability of these devices to perform simple, fast and reliable analysis, they are promising biotools for the assessment ofantioxidant properties.

Electrochemical Biosensors for the Determination of the Antioxidant Capacity in Foods and Beverages Based on Reactive Oxygen Species

An amperometric cytochrome c-based electrode was developed and applied to the quantification of the scavenging capacity of antioxidants. The enzymatic biosensor was constructed by covalently immobilizing both cyt c and XOD on a mercaptoundecanoic acid/mercaptoundecanol mixed SAMmodified screen-printed gold electrode. The concentration which induces a 50% inhibition of the superoxide level (IC50) has been determined for different substances, for instance pure substances such as ascorbic acid or Trolox, and natural sources of antioxidants, particularly orange juices and garlic extracts.