Enzymatic assays for the assessment of toxic effects of halogenated organic contaminants in water and food. A review.

Halogenated organic compounds are a particular group of contaminants consisting of a large number of substances, and of great concern due to their persistence in the environment, potential for bioaccumulation and toxicity. Some of these compounds have been classified as persistent organic pollutants (POPs) under The Stockholm Convention and many toxicity assessments have been conducted on them previously. In this work we provide an overview of enzymatic assays used in these studies to establish toxic effects and dose-response relationships. Studies in vivo and in vitro have been considered with a particular emphasis on the impact of halogenated compounds on the activity of relevant enzymes to the humans and the environment. Most information available in the literature focuses on chlorinated compounds, but brominated and fluorinated molecules are also the target of increasing numbers of studies. The enzymes identified can be classified as enzymes: i) the activities of which are affected by the presence of halogenated organic compounds, and ii) those involved in their metabolisation/detoxification resulting in increased activities. In both cases the halogen substituent seems to have an important role in the effects observed. Finally, the use of these enzymes in biosensing tools for monitoring of halogenated compounds is described.

Inhibited enzymatic reaction of crosslinked lactate oxidase through a pH-dependent mechanism.

Lactate oxidase (LOx), recognized to selectively catalyze the lactate oxidation in complex matrices, has been highlighted as preferable biorecognition element for the development of lactate biosensors. In a previous work, we have demonstrated that LOx crosslinking on a modified screen-printed electrode results in a dual range lactate biosensor, with one of the analysis linear range (4 to 50 mM) compatible with lactate sweat levels. It was advanced that such behavior results from an atypical substrate inhibition process. To understand such inhibition phenomena, this work relies in the study of LOx structure when submitted to increased substrate concentrations. The results found by fluorescence spectroscopy and dynamic light scattering of LOx solutions, evidenced conformational changes of the enzyme, occurring in presence of inhibitory substrate concentrations. Therefore, the inhibition behavior found at the biosensor, is an outcome of LOx structural alterations as result of a pH-dependent mechanism promoted at high substrate concentrations.

Cathodic stripping voltammetric determination of iodide using disposable sensors.

The World Health Organization considers iodide deficiency diseases (IDD) to be a public health problem. The main indicator to access IDD is urinary iodide, since approximately 90% of the ingested iodide uses this clearance path, with urine being a preferable target for the analysis. In this work, two screen-printed carbon electrode (SPCE) based sensors were developed to determine iodide by using only a single drop of sample. A first approach based on a SPCE proves to selectively determine iodide through the control of the cathodic stripping voltammetric (CSV) parameters. However, this strategy exhibits a gap in determining trace iodide concentrations, which is improved by modifying the working electrode surface with a chitosan coating. The performance of this new CS/SPCE-based sensor was compared with that of the previous SPCE-based sensor, showing improved iodide determination sensitivity. A limit of detection of 1.0 × 10-8 M and a linear analysis range of 0.15-500 µM were achieved with this sensor. The application of both sensors to real-life samples found values close to those determined by the standard Sandell-Kolthoff spectrophotometric method, proving them to be powerful analytical tools for iodide determination in different kinds of samples, including biological matrices.

Development of a selective chloride sensing platform using a screen-printed platinum electrode.

A new and selective voltammetric method for chloride determination is proposed, based on platinum and chloride interactions. A screen-printed platinum electrode (SPPtE) functions as a sensing platform, which promotes the formation of chloro-adsorbed species on the electrode surface, acting as an effective means of anion-determination in several matrices. The pretreatment of the SPPtE and careful control of the cathodic stripping voltammetric parameters yielded a well-defined electrochemical signal. This cathodic peak was due to the adsorption of chlorine, which had previously been oxidized from chloride anions in the initial anodic deposition step. It offers a simple, low-cost, fast, reproducible (RSD < 6%) and precise method for selective chloride determination, with limit of detection of 0.76 mM, and a sensitivity of - 24.147 µA mM -1 for a broad determination range of up to 150 mM. Chloride determination was correctly performed with single drops of environmental, pharmaceutical and food samples. In addition, the sensor was successfully adapted as a flexible screen-printed platinum electrode sensor using Gore-Tex® as support for printing.

Dual range lactate oxidase-based screen printed amperometric biosensor for analysis of lactate in diversified samples.

Lactate concentration is studied as an indicator of physical performance in sports activities, and is also analyzed in health care applications, as well as in the food and cosmetic industries. This organic acid is routinely determined in different concentration ranges, depending on the type of samples for analysis. This paper describes the development of a screen-printed lactate oxidase (LOx) based biosensor to determine lactate in broad concentration range. The Cu-MOF (copper metallic framework) crosslinking of 0.25U LOx in a chitosan layer, allows to determine the enzymatic product generated on a platinum modified working electrode, at 0.15 V (vs SPE Ag/AgCl). The biosensor responds linearly in two different concentration ranges: a first catalysis range of 14.65 µA mM-1, from 0.75 µM to 1 mM, followed by a saturation zone from 1 to 4 mM, after which a substrate enzymatic inhibition of 0.207 µA mM-1, is observed up to 50 mM. These two ranges of analysis would allow the biosensor to be used for the determination of lactate in different types of samples, with low and high content of lactate. The method reproducibility was kept below 7% and a limit of detection of 0.75 µM was obtained. The device was successfully used in the determination of lactate in sweat and saliva, as a low cost noninvasive analysis, and also in wine samples.