Pesticides, detection

Rao et al. reported on the separation and amperometric detection of several V-methyl carbamate pesticides using diamond electrodes [63]. The 

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Cyclic voltammetric i-E curves for 25 jun horse heart cytochrome c in 50 mM NaCl + Tris HCl buffer, pH 7.2 at a boron-doped diamond thin-film electrode deposited on quartz. Scan rate = 0.1 V/s. Electrode area = 0.2 cm.  

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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 ... 

Senseman SA, Lavy TE, Mattice JD, et al. 1997. Trace level pesticide detections in Arkansas surface waters. Environ Sci Technol 31 395. 

J.D. Martin, Variability of Pesticide Detections and Concentrations in Field Replicate Water Samples Collected for the National Water-quality Assessment Program, 1992-97, USGS WRI 01-4178. US Geological Survey, Washington, DC (2001). Also available on the World Wide Web http //water.wr.usgs.gov/pnsp/, accessed August 2002. 

Haberl [8] volatile chlorinated hydrocarbons, PCB and pesticides detected limits for each volatile compounds ... 

Detailed information on multiple residues in different foods is reported each year in an appendix table in the PDP summary report entitled Number of pesticides detected per sample . For example, Appendix K in the 2004 PDP report reports that almost 11% of the 12,446 samples tested contained four or more residues, while over 12% of the sweet bell peppers tested contained seven or more residues. 

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 ... 

Acetylcholinesterase (AChE) isolated from various organisms has been used in the majority of pesticide biosensors. In the early 1950s potentiometric detection was adopted for pesticide detection. In the middle of the 1980s it was used for the construction of the first integrated biosensors for detection of pesticides based on inhibition of AChE. Later rapid changes in science and technology introduced novel genetically... 

Acetylcholine + H20 AChE> Choline + Acetic acid Choline + Oz + HzO COx >- Betaine + H202 FIGURE 2.3 Bienzymatic reaction for pesticide detection. 

FIGURE 2.4 Acid phosphatase and GOD bioenzymatic reaction for pesticide detection. 

MWNTs favored the detection of insecticide from 1.5 to 80 nM with a detection limit of InM at an inhibition of 10% (Fig. 2.7). Bucur et al. [58] employed two kinds of AChE, wild type Drosophila melanogaster and a mutant E69W, for the pesticide detection using flow injection analysis. Mutant AChE showed lower detection limit (1 X 10-7 M) than the wild type (1 X 10 6 M) for omethoate. An amperometric FIA biosensor was reported by immobilizing OPH on aminopropyl control pore glass beads [27], The amperometric response of the biosensor was linear up to 120 and 140 pM for paraoxon and methyl-parathion, respectively, with a detection limit of 20 nM (for both the pesticides). Neufeld et al. [59] reported a sensitive, rapid, small, and inexpensive amperometric microflow injection electrochemical biosensor for the identification and quantification of dimethyl 2,2 -dichlorovinyl phosphate (DDVP) on the spot. The electrochemical cell was made up of a screen-printed electrode covered with an enzymatic membrane and combined with a flow cell and computer-controlled potentiostat. Potassium hexacyanoferrate (III) was used as mediator to generate very sharp, rapid, and reproducible electric signals. Other reports on pesticide biosensors could be found in review [17],... 

M. Snejdakova, L. Svobodova, D.P. Nikolelis, J. Wang, and D. Hianik, Acetylcholine biosensor based on dendrimer layers for pesticides detection. Electroanalysis 15, 1185—1191 (2003). 

A. Vakurov, C.E. Simpson, C.L. Daly, T.D. Gibson, and P.A. Millner, Acetylcholinesterase-based biosensor electrodes for organophosphate pesticide detection I. Modification of carbon surface for immobilization of acetylcholinesterase. Biosens. Bioelectron. 20, 1118-1125 (2004). 

P.R.B. de O Marques, G.S. Nunes, T.C.R. dos Santos, S. Andreescu, and J.L. Marty, Comparative investigation between acetylcholinesterase obtained from commercial sources and genetically modified Drosophila melanogaster application in amperometric biosensors for methamidophos pesticide detection. Biosens. Bioelectron. 20, 825-832 (2004). 

Other studies further indicate that the occurrence of endrin in the U.S. food supply is very low. In a 1990-91 FDA survey of pesticide residues in milk representing most of the U.S. supply consumed in metropolitan areas, endrin was detected at trace levels (0.0005-0.001 ppm [0.5-1.0 ppb]) in only 2 of 806 composite samples (one sample each from Atlanta, Georgia and Dover, Delaware) (Trotter and Dickerson 1993). In another statistically based FDA study in 1992-93, endrin was not found as a violative residue in any of 710 domestic or 949 imported pear samples (Roy et al. 1995). Endrin was not reported among the pesticides detected in a 1994 FDA survey of pesticide levels in 160 samples of catfish, crayfish, shrimp, trout, salmon, oysters, and various other species from important aquaculture areas of the United States (FDA 1995). Comparable results were found in similar studies conducted by the FDA in 1990-93 (FDA 1995). 

A huge number of immunoassays for pesticides detection in water and food have been presented during the last decades, and different review articles have been revised it [100-109]. 

Environmental applications of HRP include immunoassays for pesticide detection and the development of methods for waste water treatment and detoxification. Examples of the latter include removal of aromatic amines and phenols from waste water (280-282), and phenols from coal-conversion waters (283). A method for the removal of chlorinated phenols from waste water using immobilised HRP has been reported (284). Additives such as polyethylene glycol can increase the efficiency of peroxidase-catalyzed polymerization and precipitation of substituted phenols and amines in waste or drinking water (285). The enzyme can also be used in biobleaching reactions, for example, in the decolorization of bleach plant effluent (286). 

Pesticides Detected In University of California Evaporation Beds Using Gas Chromatography with Specific Element Detectors... 

The pesticides found in fruit products are given in Exhibit 5, and the industrial chemicals are given in Exhibit 6. Fruit products are contaminated with a significant number of diverse insecticides and fungicides. However, several of these pesticides are responsible for the majority of the contamination. Iprodione and its metabolite make up 44.6 percent of the pesticides detected, whereas endosulfan and its by-product (endosulfan sulfate) make up an additional 24.4 percent of the detected pesticides, for a total of 69 percent. The remaining five pesticides are distributed throughout the fruit products. 

Earlier work in this field [28] indicated that acetylcholinesterase enzymes would be suitable biomolecules for the purpose of pesticide detection, however, it was found that the sensitivity of the method varied with the type and source of cholinesterase used. Therefore the initial thrust of this work was the development of a range of enzymes via selective mutations of the Drosophila melanogaster acetylcholinesterase Dm. AChE. For example mutations of the (Dm. AChE) were made by site-directed mutagenesis expressed within baculovirus [29]. The acetylcholinesterases were then purified by affinity chromatography [30]. Different strategies were used to obtain these mutants, namely (i) substitution of amino acids at positions found mutated in AChE from insects resistant to insecticide, (ii) mutations of amino acids at positions suggested by 3-D structural analysis of the active site,... 

Early results indicate a high sensitivity for pesticide detection, with the system being capable of detecting dichlorvos at concentrations as low as 1 x 10-17M and parathion and azinphos both at concentrations as low as 1 x 10-16M [40]. 

J.-L. Marty, D. Garcia and R. Rouillon, Biosensors potential in pesticides detection, Trends. Anal. Chem., 14 (1995) 3329-3333. 

Acetylcholinesterase inhibition has been widely used for pesticide detection [88-94], but less exploited than protein phosphatase inhibition for cyanobacterial toxin detection. Nevertheless, the anatoxin-a(s) has more inhibition power than most insecticides, as demonstrated by the higher inhibition rates [95]. In order to detect toxin concentrations smaller than usually, mutant enzymes with increased sensitivity were obtained by genetic engineering strategies residue replacement, deletion, insertion and combination of mutations. Modifications close to the active site, located at the bottom of a narrow gorge, made the entrance of the toxin easier and enhanced the sensitivity of the enzyme. 

Moreover, the use of PB will not only be limited to the detection of H202 and its use in conjunction with oxidase enzymes. A recent disclosure of the electrocatalytic activity of PB towards the oxidation of thiols will also be discussed and an application with acetylcholinesterase enzymes for pesticide detection reported. 

Scheme 1. Schematic representation of the system adopted for glucose and pesticide detection. In the upper part of the scheme is shown the reaction chain for the detection of acetylthiocholine giving a measure of acetylcholinesterase (AChE) activity which can be related to pesticide content. In the lower part of the scheme is shown the classic reaction utilised in the case of an oxidase enzyme (glucose oxidase—GOx) for the detection of glucose. In the first case, the final product is thiocholine and in the second, H202, both are measured at the Prussian blue modified electrode at an applied potential of 0.2 V vs. Ag/AgCl and —0.05 V vs. Ag/AgCl, respectively.

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