Pesticides enzyme sensors

JL Martin, N Mionetto, T Noguer, F Ortega, C Roux. Enzyme sensors for the detection of pesticides. Biosensors Bioelectronics 8 273-280, 1993. 

The result for chlorpyrifos in RM08 was gained by an enzyme sensor with amper-ometric detection. However, since the sensitivity of the sensor is not sufficient to differentiate between chlorpyrifos and chlorfenvinfos, and both were present in the sample, the outlying position of the result (indicated on Figure 5.2.3 - laboratory code 69) in the chlorpyrifos population is understandable. This method is currently under improvement with recombinant enzymes to gain specificity for various organophos-phorus pesticides. 

Abstract. The biosensors described in this work, for the monitoring of pesticides, are based on acetylcholinesterase immobilized on the surface of screen-printed electrodes. The principle of the biosensor is that the degree of inhibition of an enzyme sensor by a pesticide is dependent on the concentration of that pesticide. The DPV technique was used as a detection method and methyl-paraoxon as a reference pesticide for sensor calibration. 

Nabok A., Haron S., and Ray A., Registration of heavy metal ions and pesticides with ATR planar waveguide enzyme sensors, Appl. Surf. Sci., 238(1-4), 423-428, 2004. 

Enzyme/indicator optrodes for registration of enzyme reactions and their inhibitors, such as heavy metal ions and pesticides, can be produced by PESA technique. Composite films containing the enzyme urease and cyclo-tetra-chromotropylene as indicator molecules show some characteristic spectral transformations caused by urea decomposition. The reaction of inhibition of urease by heavy metal ions can be also registered with this method. Further development of the enzyme sensors and sensor arrays lies in finding suitable pairs of enzyme/indicator, their deposition by PESA method and studying the enzyme reactions (including inhibition) with UV-vis spectroscopy. 

Periasamy, A.P., Umasankar, Y, Chen, S.M., 2009. Nanomaterials—acetylcholinesterase enzyme matrices for organophosphorus pesticides electrochemical sensors a review. Sensors 9 (6), 4034M055. 

Schoning MJ, Arzdorf M, Mulchandani P, Chen W, Mulchandani A (2003) Towards a capacitive enzyme sensor for direct determination of organophosphorus pesticides fundamental studies and aspects of development. Sensors 3 119-127... 

Figure 8.9 Simplified flow-chart representing the operation of the automated determination of pesticides by an enzyme sensor.

Periasamy AP, Umasankar Y, Chen S (2009) Nanomaterials - acetylcholinesterase enzyme matrices for organophosphoms pesticides electrochemical sensors a review. Sensors 9 4034 055... 

Biosensors ai e widely used to the detection of hazardous contaminants in foodstuffs, soil and fresh waters. Due to high sensitivity, simple design, low cost and real-time measurement mode biosensors ai e considered as an alternative to conventional analytical techniques, e.g. GC or HPLC. Although the sensitivity and selectivity of contaminant detection is mainly determined by a biological component, i.e. enzyme or antibodies, the biosensor performance can be efficiently controlled by the optimization of its assembly and working conditions. In this report, the prospects to the improvement of pesticide detection with cholinesterase sensors based on modified screen-printed electrodes are summarized. The following opportunities for the controlled improvement of analytical characteristics of anticholinesterase pesticides ai e discussed ... 

Biosensors may provide the basis for in-field analyses and real-time process analysis. However, biosensors are generally limited to the determination of a limited range of analytes in defined matrices. Enzyme-based biosensors, principally acetylcholinesterase (AChE) inhibition, have been successfully used in environmental analysis for residues of dichlorvos and paraoxon, " carbaryl " and carbofuran. " Immunochemically based biosensors may be the basis for the determination of pesticide residues in liquid samples, principally water and environmental samples, but also fruit juices. The sensors can be linked to transducers, for example based on a piezo-... 

Trettnak W., Reininger F., Zinterl E., Wolfbeis O.S., Fiber Optic Remote Detection of Pesticides and Related Inhibitors of the Enzyme Acetylcholine Esterase, Sensor Actuat B-Chem 1993 11 87. 

Enzymes can be used not only for the determination of substrates but also for the analysis of enzyme inhibitors. In this type of sensors the response of the detectable species will decrease in the presence of the analyte. The inhibitor may affect the vmax or KM values. Competitive inhibitors, which bind to the same active site than the substrate, will increase the KM value, reflected by a change on the slope of the Lineweaver-Burke plot but will not change vmax. Non-competitive inhibitors, i.e. those that bind to another site of the protein, do not affect KM but produce a decrease in vmax. For instance, the acetylcholinesterase enzyme is inhibited by carbamate and organophosphate pesticides and has been widely used for the development of optical fiber sensors for these compounds based on different chemical transduction schemes (hydrolysis of a colored substrate, pH changes). 

Absorbance- and reflectance-based measurements are widespread, as there are many enzymatic reaction products or intermediates that are colored or if not, can react with the appropriate indicator. Sensors using acetylcholinesterase for carbamate pesticides detection are an example of indirect optical fiber biosensors. This enzyme catalyses the hydrolysis of acetylcholine with concomitant decrease in pH41 ... 

The design and implementation of a portable fiber-optic cholinesterase biosensor for the detection and determination of pesticides carbaryl and dichlorvos was presented by Andreou81. The sensing bioactive material was a three-layer sandwich. The enzyme cholinesterase was immobilized on the outer layer, consisting of hydrophilic modified polyvinylidenefluoride membrane. The membrane was in contact with an intermediate sol-gel layer that incorporated bromocresol purple, deposited on an inner disk. The sensor operated in a static mode at room temperature and the rate of the inhibited reaction served as an analytical signal. This method was successfully applied to the direct analysis of natural water samples (detection and determination of these pesticides), without sample pretreatment, and since the biosensor setup is fully portable (in a small case), it is suitable for in-field use. 

In AChE-based biosensors acetylthiocholine is commonly used as a substrate. The thiocholine produced during the catalytic reaction can be monitored using spectromet-ric, amperometric [44] (Fig. 2.2) or potentiometric methods. The enzyme activity is indirectly proportional to the pesticide concentration. La Rosa et al. [45] used 4-ami-nophenyl acetate as the enzyme substrate for a cholinesterase sensor for pesticide determination. This system allowed the determination of esterase activities via oxidation of the enzymatic product 4-aminophenol rather than the typical thiocholine. Sulfonylureas are reversible inhibitors of acetolactate synthase (ALS). By taking advantage of this inhibition mechanism ALS has been entrapped in photo cured polymer of polyvinyl alcohol bearing styrylpyridinium groups (PVA-SbQ) to prepare an amperometric biosensor for... 

S. Andreescu, V. Magearu, A. Lougarre, D. Fournier, and J.L. Marty, Immobilization of enzymes on screen-printed sensors via a histidine tail. Application to the detection of pesticides using modified cholinesterase. Anal. Lett. 34, 529-540 (2001). 

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