Montserrat Cortina-Puig

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.

The use of Artificial Neural Networks for the selective detection of two organophosphate insecticides: chlorpyrifos and chlorfenvinfos.

Amperometric acetylcholinesterase (AChE) biosensors have been developed to resolve mixtures of chlorpyrifos oxon (CPO) and chlorfenvinfos (CFV) pesticides. Three different biosensors were built using the wild type from electric eel (EE), the genetically modified Drosophila melanogaster AChE B394 and B394 co-immobilized with a phosphotriesterase (PTE). Artificial Neural Networks (ANNs) were used to model the combined response of the two pesticides. Specifically two different ANNs were constructed. The first one was used to model the combined response of B394+PTE and EE biosensors and was applied when the concentration of CPO was high and the other, modelling the combined response of B394+PTE and B394 biosensors, was applied with low concentrations of CPO. In both cases, good prediction ability was obtained with correlation coefficients better than 0.986 when the obtained values were compared with those expected for a set of six external test samples not used for training.

Characterization of the gold-catalyzed deposition of silver on graphite screen-printed electrodes and their application to the development of impedimetric immunosensors.

This paper describes the characterization of the gold-catalyzed deposition of silver on graphite screen-printed electrodes (SPEs) using electrochemical impedance spectroscopy (EIS) and the application of this approach to the development of impedimetric immunosensors. After applying -0.1 V for 45 s, the amount of electrodeposited silver quantitatively changes the magnitude of two elements of the electrical equivalent circuit: the interface capacitance, Ci, and the charge-transfer resistance, R(CT). Better correlations have been found when considering the R(CT) since this parameter is almost exclusively dependent on the amount of deposited silver under these experimental conditions. This approach has been successfully applied to the development of an impedimetric immunosensor for aflatoxin M(1). The R(CT) magnitude shows good correlation with the amount of gold immobilized on the electrode surface after a competitive assay and thus, with the toxin concentration. This approach has been found sensitive in a wide range of concentrations, from 15 to 1000 free-AFM(1) ppt with a limit of detection of 12 ppt.

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.

Analysis of Pesticide Mixtures using Intelligent Biosensors

Pesticides are widely used in agricultural crops, forests and wetlands as insecticides, fungicides, herbicides and nematocides. Many of them are considered to be particularly hazardous compounds and toxic because they inhibit fundamental metabolic pathways. Due to their high acute toxicity and risk towards the population, some directives have been established to limit the presence of pesticides in water and food resources. Concerning the quality of water for human consumption, the European Council directive 98/83/CE (Drinking Water Directive) has set a maximum admissible concentration of 0.1 μg L-1 per pesticide and 0.5 μg L-1 for the total amount of pesticides. Organophosphates (OPs) are a class of synthetic pesticides developed from the Second World War, which are used as insecticides and nerve agents (Bajgar et al., 2004; Raushel, 2002). Since the removal of organochlorine insecticides from use, OPs have become the most widely used insecticides. They are normally used for agricultural, industrial, household and medical purposes. OPs poison insects and mammals by phosphorylation of the acetylcholinesterase (AChE) enzyme at nerve endings (Dubois, 1971; Ecobichon, 2001). Inactivation of this enzyme results in an accumulation of acetylcholine leading to an overstimulation of the effector organ (Aldridge, 1950; Reigart et al., 1999). The hazardous nature of OPs and their wide usage has led to concerted efforts for developing highly sensitive detection techniques as well as efficient destruction methods for these compounds (Gill et al., 2000). Detection techniques are fundamental in order to accurately determine the level of contamination of waters by pesticides. They are classically based on extraction, cleanup and analysis using gas chromatography (GC) or liquid chromatography (LC) coupled to sensitive and specific detectors (Ballesteros et al., 2004; Geerdink et al., 2002; Kuster et al., 2006; Lacorte et al., 1993). Although they are very sensitive, these techniques are expensive and time consuming (involve extensive preparation steps), they are not adapted for in situ and real time detection and often require highly trained personnel. In addition, these methods are not able to provide any information concerning the toxicity of the sample. AChE biosensors appear as a rapid and simple alternative method for the detection of OPs insecticides. A successful AChE biosensor for toxicity monitoring should offer comparable Source: Intelligent and Biosensors, Book edited by: Vernon S. Somerset, ISBN 978-953-7619-58-9, pp. 386, January 2010, INTECH, Croatia, downloaded from SCIYO.COM

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.