Acetylcholinesterase sensor

E. Suprun, G. Evtugyn, H. Budnikov, F. Ricci, D. Moscone and G. Pell-eschi, Acetylcholinesterase sensor based on screen-printed carbon electrode modified with Prussian blue, Anal. Bioanal. Chem., 383 (2005) 597-604. 

Snejdarkova M, SvobodovaL, Evtugyn G, Budnikov H, Karyakin A, Nikolelis DP, Hianik T (2004) Acetylcholinesterase sensors based on gold electrodes modified with dendrimer and polyaniline-a comparative research. Anal Chim Acta514(l) 79-88. doi 10.1016/j.aca.2004. 03.019... 

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-... 

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 ... 

A.K. Singh, A.W. Flounders, J.V. Volponi, C.S. Ashley, K. Wally, and J.S. Schoeniger, Development of sensors for direct detection of organophosphates. Part I immobilization, characterization and stabilization of acetylcholinesterase and organophosphate hydrolase on silica supports. Biosens. Bioelectron. 14, 703-713 (1999). 

In this system, choline formed by acetylcholinesterase is oxidized by choline oxidase and the hydrogen peroxide produced is determined using the luminol/peroxidase CL reaction. The sensor has been used for the analysis of Paraoxon and Aldicarb pesticides, with detection limits of 0.75 pg/L and 4 pg/ L, respectively. Recoveries in the range of 81-108% in contaminated samples of soils and vegetables were obtained. 

There are problems with this approach since enzymes isolated from natural sources such as the electric organ of electric eels often display low sensitivity and selectivity to the wide range of potential pesticide targets [21]. A possible solution to this is the development of a multisensor array where a variety of genetically modified acetylcholinesterases are immobilised on an array of electrochemical sensors and the responses from these are then processed via a neural network. 

S. Andreescu, A. Avramescu, C. Bala, V. Magearu and J.-L. Marty, Detection of organophosphorus insecticides with immobilised acetylcholinesterase—comparative study of two enzyme sensors, Anal. Bioanal. Chem., 374 (2002) 39-45. 

S. Andreescu, D. Fournier and J.-L. Marty, Development of highly sensitive sensor based on bioengineered acetylcholinesterase immobilized by affinity method, Anal. Lett., 36 (2003) 1865-1885. 

G.S. Nunes, T. Montesinos, P.B.O. Marques, D. Fournier and J.-F. Marty, Acetylcholine enzyme sensor for determining methamidophos insecticide evaluation of some genetically modified acetylcholinesterases from Drosophila melanogaster, Anal. Chim. Acta, 434 (2001) 1-8. 

Screen-printed electrochemical sensors for the detection of acetylcholinesterase inhibitors... 

Acetylcholine Sensors. The general scheme for determination of the neurotransmitter acetylcholine is outlined in Figure 11. In this scheme, acetylcholine is first converted catalytically to choline by the enzyme acetylcholinesterase. The choline produced reduces the FAD redox centers of choline oxidase, and electron transfer from these centers to the electrode is facilitated by the polymeric relay system. 

Figures 12-14 show the steady-state current dependence of the acetylcholine sensors on substrate concentration these sensors contained polymers C, F, and I, respectively, as the electron relay systems. For an applied potential of +250 mV vs. SCE, the time required to reach 95% of the steady-state current was typically 10-15 sec after addition of the acetylcholine sample. At lower potentials, the response time was slightly slower. For these systems, a detection limit (as defined by a signal-to-noise ratio of approximately 2) of approximately 0.5 to 1.0 /xM was achieved under N2-saturated conditions. The response of the sensors to choline was nearly identical to the acetylcholine response, which demonstrates the efficient conversion of acetylcholine to choline by acetylcholinesterase.

Sensors that use an antibody to detect OP-butyr-ylcholinesterase or OP-acetylcholinesterase adducts are being developed but are not yet commercially available. 

Acetylcholinesterase - Nanomaterials Hybrid Sensors for the Detection of Organophosphorous and Carbamate Pesticides... 

Keywords acetylcholinesterase, electrochemical sensors, organophosphate, carbamate, pesticide, thiocholine, acetylthiocholine, nano materials... 

The propidium sensor setup (see Subheading 3.3.4) can also be utilized to monitor the activity of the surface-bound acetylcholinesterase. The original measuring cycle is extended by the injection of substrate solution and an additional washing step ... 

Caetano J, Machado SAS. Determination of carbaryl in tomato "in natura" using an amperometric biosensor based on the inhibition of acetylcholinesterase activity. Sensor Actuat B-Chem 2008 B129 40-6. 

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. 

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