Acetylcholinesterase sensor based on screen-printed carbon electrode modified with prussian blue

Electrochemical biosensor technology: application to pesticide detection

In recent years, electrochemical sensors and biosensors are becoming an accepted part of analytical chemistry since they satisfy the expanding need for rapid and reliable measurements. An area in which electrochemical biosensors perhaps show the greatest diversity and potential for development involves the measurement of environmentally significant parameters. The increasing number of pollutants in the environment calls for fast and cost-effective analytical requirements. In this context, biosensors appear as suitable alternative or complementary analytical tools. The aim of this chapter is to review some basic concept concerning the electrochemical biosensors and to illustrate a protocol for the detection of environmental organic pollutants on the basis of electrochemical biosensors. In particular, a method based on the inhibition of the enzyme acetylcholinesterase (AChE) for the detection of organophosphorus and carbamate pesticides will be described in detail.

Amperometric Biosensors for Real Time Assays of Organophosphates

An amperometric biosensor based on acetylcholinesterase (AChE) immobilized in gelatin was used to develop an assay for the organophosphate paraoxon. The more traditional manner employing preincubation was used for comparison between measurement procedures, although the aim of the study was to examine the performance of the biosensor for real time monitoring of organophosphates. The biosensor was immersed in a reaction chamber and paraoxon was injected inside. We were able to detect 200 pg of paraoxon within one minute or 2.5 ppb when the biosensor was preincubed in the sample solution for 15 minutes. The practical impact and expectations are discussed.

Suborganismic and organismic effects of aldicarb and its metabolite aldicarb-sulfoxide to the zebrafish embryo (Danio rerio)

The new European chemical regulation (REACH) requires a short-term fish test for chemicals where the level of production exceeds 10tons per year. For ethical reasons (3R-concept), an alternative to the acute fish test should be introduced to decrease the number of animal testing with fish. The zebrafish embryo (Danio rerio) test became a valuable tool in ecotoxicology and already replaces the acute fish test for the evaluation of wastewater in Germany. Recent efforts are targeted to use this and other fish embryo tests for the effect assessment of chemicals. The toxic effects of the carbamate insecticide aldicarb and its metabolite aldicarb-sulfoxide to zebrafish embryos were analysed using two approaches with different endpoints. Organismic tests were conducted with zebrafish embryos exposed to the pesticides for 48h. In addition, suborganismic effects were examined analysing the enzyme inhibition of cholinesterases and carboxylesterases. On the organismic level, the only sublethal effect seen was the increase of heart rate at low and decrease at higher concentration with the use of aldicarb-sulfoxide but not with aldicarb (concentration range 0.2-300microM). In contrast, analysis of enzyme inhibitions showed high to very high effects caused by the two carbamates. The enzyme inhibition analysis of whole homogenates of exposed embryos may be advantageous for toxicant screening (biomarker of exposure) and might be used to bridge the gap of sensitivity of the (48h old) zebrafish embryos to adult fish when exposed to anti-cholinesterase substances (biomarker of prospective effect).

Biosensors based on screen-printing technology, and their applications in environmental and food analysis

This review summarizes scientific research activity on biosensors, especially screen-printed, electrode-based biosensors. The basic configurations of biosensors based on screen-printing technology are discussed and different procedures for immobilization of the biorecognition component are reviewed. Theoretical aspects are exemplified by practical environmental and food-analysis applications of screen-printed, electrode-based biosensors.

Enzymatic Spectrophotometric Method for Aflatoxin B Detection Based on Acetylcholinesterase Inhibition

A new method for aflatoxin B (AFB) determination is proposed. The AFB determination is based on acetylcholinesterase (AChE) inhibition, and the AChE residual activity is determined using the colorimetric method (Ellman's method). Cholinesterases (ChEs) from various sources were tested using AFB1 as reference aflatoxin. AChE from electric eel has shown the highest sensitivity to AFB1, and it was chosen for the rest of the work. To select and optimize the analytical procedures, an investigation on the type of AChE inhibition by AFB1 was carried out. The AChE degree of inhibition by AFB1 was independent of the incubation time and the enzyme concentrations, showing the reversibility of the inhibition. This reversibility of the inhibition permits a rapid analysis of AFB1, requiring only 3 min. For the development of the AFB1 assay, the pH, the time of reaction, temperature, and substrate concentration were evaluated and optimized. The linear range of 10-60 ng mL-1 was determined. To evaluate the selectivity of this method, the cross-reactivity with other aflatoxins such as aflatoxin B2, aflatoxin G1, aflatoxin G2, and aflatoxin M1 was investigated. Finally, the suitability of the assay for AFB1 quantification in barley was evaluated. This study shows a new approach to detect aflatoxins based on enzyme inhibition and has advantages such as the ease of use, rapidity, and cost effectiveness. Thus, it could find a possible use as a screening method for this type of mycotoxins.

An amperometric acetylthiocholine sensor based on immobilization of acetylcholinesterase on a multiwall carbon nanotube–cross-linked chitosan composite

A simple method has been devised for immobilization of acetylcholinesterase (AChE)--covalent bonding to a multiwall carbon nanotube (MWNT)--cross-linked chitosan composite (CMC)-and a sensitive amperometric sensor for rapid detection of acetylthiocholine (ATCl) has been based on this. Fourier-transform infrared spectroscopy proved that the native structure of the immobilized enzyme was preserved on this chemically clean and homogeneous composite film, because of the excellent biocompatibility and non-toxicity of chitosan. Glutaraldehyde was used as cross-linker to covalently bond the AChE, and efficiently prevented leakage of the enzyme from the film. Because of the inherent conductive properties of the MWNT, the immobilized AChE had greater affinity for ATCl and excellent catalytic effect in the hydrolysis of ATCl, with a K(app)(m) value of 132 micromol L(-1), forming thiocholine, which was then oxidized to produce a detectable and rapid response. Under optimum conditions the amperometric current increased linearly with the increasing concentration of ATCl in the range 2.0-400 micromol L(-1), with a detection limit of 0.10 micromol L(-1). Fabrication reproducibility of the sensor was good and the stability was acceptable. The sensor is a promising new tool for characterization of enzyme inhibitors and for pesticide analysis. Abstract.

Detection of carbamic and organophosphorous pesticides in water samples using a cholinesterase biosensor based on Prussian Blue-modified screen-printed electrode

In the present paper, a comparative study using Co-phthalocyanine and Prussian Blue-modified screen-printed electrodes, has been performed. Both the electrodes have demonstrated an easiness of preparation together with high sensitivity towards thicoholine (LOD=5 x 10(-7) and 5 x 10(-6) M for Co-phthalocyanine and Prussian Blue, respectively) with high potentialities for pesticide measurement. Prussian Blue-modified screen-printed electrodes were then selected for successive enzyme immobilization due to their higher operative stability demonstrated in previous works. AChE and BChE enzymes were used and inhibition effect of different pesticides was studied with both the enzymes. AChE-based biosensors have demonstrated a higher sensitivity towards aldicarb (50% inhibition with 50 ppb) and carbaryl (50% inhibition with 85 ppb) while BChE biosensors have shown a higher affinity towards paraoxon (50% inhibition with 4 ppb) and chlorpyrifos-methyl oxon (50% inhibition with 1 ppb). Real samples were also tested in order to evaluate the matrix effect and recovery values comprised between 79 and 123% were obtained.