Sensors acetylcholine

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.

Figure 12. (left) Steady-state current response of acetylcholine sensors based on polymer C, in pH 7.0 phosphate buffer under N2-saturated conditions. Each point is the mean result for five electrodes. 

Acetylcholine sensors construction, 115 schematic representation, 120f substrate concentration, effect on response, 121/... 

One way to increase interaction between redox polymers and enzyme (i.e., glucose oxidase) known to have surface charges is to increase hydrophilicity of the polymer. To test the hypothesis, ferrocene containing polysiloxane with ethylene oxide pendant chains was prepared and their efficiency tested as glucose and acetylcholine sensors [12,81]. Glucose and... 

Tran-Minh C., Pandey P.C., Kumaran S., (1990) Studies on acetylcholine sensor and its analytical application based on the inhibition of cholinesterase. Bios. Bioelectron., 5, 461-471... 

Xue, W., Cui, T. A thin-film transistor based acetylcholine sensor using self-assembled carbon nanotubes and Si02 nanoparticles. Sens. Act. B 134, 981-987 (2008)... 

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. 

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 ... 

In addition to hydrogen ions, other species can also affect the enzymatic catalytic activity. This phenomenon is called inhibition it may be specific, nonspecific, reversible, or irreversible. The inhibition reactions can also be used for the sensing of inhibitors. The best-known example is the sensor for detection of nerve gases. These compounds inhibit the hydrolysis of the acetylcholine ester which is catalyzed by the enzyme acetylcholine esterase. Acetylcholine ester is a key component in the neurotransmission mechanism. 

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. 

Enzyme micro-electrode arrays, on exposure to differing concentrations of the substrate acetylthiocholine chloride (Fig. 24.4), demonstrate that above concentrations of 1 mM, responses tend towards a plateau. For this reason, all sensory inhibitory responses to pesticides were recorded in the presence of 2 mM acetylcholine. It should be noted that since sensor responses are recorded in the order of hundreds of nA, it is clear that some current amplification must be operating to achieve currents of this order of magnitude. This is particularly obvious when working electrodes of 0.5 cm2 were used, which only present a combined microelectrode array area of approximately 1 x 10 5 cm 2 per screen-printed electrode (if the total number of micro-electrodes that can be produced by this technique is 2 x 105 cm 2 [2-4]). 

Verhage M, Maia AS, Plomp JJ, Brussaard AB, Heeroma JH, et al. (2000) Synaptic assembly of the brain in the absence of neurotransmitter secretion. Science 287 864—9 Wonnacott S (1997) Presynaptic nicotinic ACh receptors. Trends Neurosd 20 92-8 Weber T, Zemelman BV, McNew JA, Westermann B, Gmachl M, Parlati F, Sollner TH, Rothman JE (1998) SNAREpins minimal machinery for membrane fusion. Cell 92 759-72 Whittaker VP, Sheridan MN (1965) The morphology and acetylcholine content of isolated cerebral cortical synaptic vesicles. J Neurochem 12 363-72 Xu J, Mashimo T, Siidhof TC (2007) Synaptotagmin-1, -2, and -9 Ca2+ sensors for fast release that spedfy distinct presynaptic properties in subsets of neurons. Neuron 54 567-81 Zucker RS, Regehr WG (2002) Short-term synaptic plasticity. Annu Rev Physiol 64 355 405... 

Chaki S, Muramatsu M, Otomo S (1994) Involvement of protein kinase C activation in regulation of acetylcholine release from rat hippocampal slices by minaprine. Neurochem Int 24 37-41 Chameau P, Van d, V, Fossier P et al (2001) Ryanodine-, IP3- and NAADP-dependent calcium stores control acetylcholine release. Pflugers Arch 443 289-96 Chapman ER (2002) Synaptotagmin a Ca(2+) sensor that triggers exocytosis Nat Rev Mol Cell Biol 3 498-508... 

The construction and response of amperometric biosensors for glucose, acetylcholine, and glutamate based on these polymeric materials are described, and the dependence of sensor response on the polymer structure is discussed. 

Hale et al. reported the use of an enzyme-modified carbon paste for the determination of acetylcholine [21], The sensor was constructed from a carbon paste electrode containing acetylcholineesterase and choline oxidase, and the electron transfer mediator tetrathiafulvalene. The electrode was used for the cyclic voltammetric determination of acetylcholine in 0.1 M phosphate buffer at +200 mV versus saturated calomel electrode. Tetrathiafulvalene efficiently re-oxidized the reduced flavin adenine dinucleotide centers of choline oxidase. The calibration graph was linear up to 400 pM acetylcholine, and the detection limit was 0.5 pM. 

Choline oxidase and acetylcholineesterase Enzymes immobilized on a nylon net attached to H202-selective amperometric sensor. ChO is used for choline and AChE and ChO for acetylcholine. Rectilinear response in the range of 1-10 pM. Response time 1-2 min. Interferences occur from ascorbic acid, primary amines, and most seriously from betaine aldehyde. [64]... 

Acetylcholine receptor from electric organ of Torpedo sp. Receptor protein noncovalently bound on the surface of a planar interdigitated capacitative sensor. Response was concentration dependent and specific for ACh and inhibited by (+ )-tubocurarine, amantidine and a-neurotoxin. [66]... 

Acetylcholineesterase Anal Abst., 1988, 50, 6J174 Sensor previously described. Determination of ACh and Ch in rats brain extracts. Rectiliner calibration graphs were obtained for 12-190 pM acetylcholine. Response times, 2 min. Recoveries were 93-105% of ACh. Used for determination of ACh in ophthalmic preparations. [67]... 

Acetylcholineesterase and choline oxidase Co-immobilizing AChE and ChO on to a Pt disc microelectrode (200 tM diameter) with glutaraldehyde vapor. Sensor was used in flow-injection and LC system at a potential of 0.6 V versus Ag/AgCl/ KC1 (saturated) with mobile phase containing 0.1 M-phosphate buffer (pH 8) (for FIA) and 0.05 M phosphate buffer at pH 7.5 containing 0.03 mM SDS and 3mM tetramethyl ammonium chloride (for LC). The LC separations were carried out on an ODS-5 column (25 cm x 0.5 mm i.d.). The microsensor exhibited a linear response for acetylcholine and choline for 0.05-103 pmol. [87]... 

Acetylcholineesterase A 3 mm diameter, Pt disc electrode, either polished or black, was immersed for 20 min in a solution of avidin (lOOpg/mL). After washing with PBS solution of pH 7.4, the electrode was immersed for 20 min in a biotin-labeled ChO solution (lOOpg/mL). After treatment 10 times, the surface of the sensor was further modified with ChE in the same manner. The amperometric response of the sensor was measured with a three-electrode cell at 0.6 V versus Ag/ AgCl in 0.1 M phosphate buffer of pH 6.8. The response was linear from 1 pM to 1 mm of acetylcholine. [102]... 

Acetylcholineesterase A stock solution of 0.52mg/mL of the pesticide trichlorophen in lOmM phosphate buffer of pH 7.5 was diluted with buffer to various concentrations. The obtained solutions were then analyzed using an ACh biosensor based on the inhibition effect of trichlorophen on the function AChE which promotes the hydrolysis of the natural neurotransmitter, acetylcholine. The sensor was fabricated by immobilizing AChE onto the surface of an antimony disc electrode, which was then used in conjunction with a double junction Ag/AgCl (0.1 M-KC1) reference electrode with a 0.1 M lithium acetate salt bridge. 

Acetylcholineesterase and choline oxidase Sensors were developed consisting of a Clarke oxygen electrode modified by superposition (over the polypropylene membrane of the electrode) of a dialysis membrane on which AChE and ChO were immobilized. Both formats are based on the conversion of the substrate to choline which is oxidized in the presence of choline oxidase causing a reduction in p02 which is detected by the electrode. Free choline is measured with a similar electrode with only choline oxidase immobilized on the membrane. Calibration graphs were rectilinear upto 90 pM choline and upto 120 pM acetylcholine. Results were presented for the analysis of tissue extracts and pharmaceutical formulations. [115]... 

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