Cholinesterases based sensors

Ultrasensitive determination of pesticides via cholinesterase-based sensors for environmental analysis... 

Generally, few limitations for these systems have been explored in the literature, including damaging of the sensor by any factor that will affect the enzymatic activity or other reactions used in the method and the inability to recognize the inhibitor using such cholinesterase-based sensor. Therefore, in addition to cholinesterase-based sensors, many other sensors and methods have been developed and used to delect anti-ChEs in the past, each with its own advantages and disadvantages (reviewed by Kim et al., 2011). Anti-ChE detection methods thus should be tailored to the specific anti-ChEs and the requirements from the sensor. 

A. Ivanov, G. Evtugyn, L.V. Lukachova, E.E. Karyakina, HC. Budnikov, S.G. Kiseleva, A.V. Orlov, G.P. Karpacheva, and A.A. Karyakin, Cholinesterase potentiometric sensor based on graphite screen-printed electrode modified with processed polyaniline. IEEE Sensors J. 3, 333-340 (2003). 

Cholinesterase based bioreactor for determination of pesticides Sensors Actuators B 18-19 689-93... 

Different technologies and methods based on cholinesterases have been developed for low cost and fast detection of anti-ChEs with high sensitivity, accuracy and storage stability (Periasamy et al., 2009). These include a novel development of cholinesterases conjugated to nanomaterial-based sensors. In such systems, the cholinesterases are conjugated to nanomaterials such as carbon nanotubes (CNTs), metallic nanoparticles (NPs), or semiconductor NPs, which enable the use of their unique properties, in the nano regime, to achieve the requirements from satisfactory sensors. 

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 ... 

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... 

A. Ivanov, G. Evtugyn, H. Budnikov, F. Ricci, D. Moscone, and G. Palleschi, Cholinesterase sensors based on screen-printed electrodes for detection of organophosphorus and carbamic pesticides. Anal. Bioanal. Chem. 377, 624-631 (2003). 

G.A. Evtyugin, I.I. Stoikov, C.K. Budnikov and E.E. Stoikova, A cholinesterase sensor based on a graphite electrode modified with 1,3-disub-stituted calixarenes, J. Anal. Chem., 58 (2003) 1151-1156. 

P. Skladal and M. Mascini, Sensitive detection of pesticides using am-perometric sensors based on cobalt phthalocyanine-modified composite electrodes and immobilised cholinesterase, Biosens. Bioelectron, 7 (1992) 335-343. 

With regard to assaying the inhibitory activity of extracts electro-chemically, one of the problems of assays using sensors based on cholinesterase was that considerable time, e.g. 30-45 min [46,47], could be needed for the activity of the enzyme electrode to fall below control levels. The time increased as the level of inhibition decreased. Such lengthy assays make any number of serial assays impractical. In previous work [48,49], it had been noted that if sensors were exposed to solution containing inhibitors and then allowed to dry, they could be... 

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... 

Carboxypeptidase A (approx. 35 kDa MW, Sigma Chemical) functions both as a peptidase and an esterase it is in this latter mode that it can serve as a detector for cholinesterase inhibitors. Unlike the other enzymes such as AChE or BChE, it does not have a serine residue in the active site. TPPSi forms a complex with the enzyme and, upon challenge with the cholinesterase inhibitor eserine (physostigmine) in water, exhibits a change in the absorbance spectrum with a new peak and a marked increase in absorbance at 423 nm. This suggests TPPS, may not be completely displaced from the active site. For actual sensor operations, the use of an enzyme such as BChE or carboxypeptidase in place of (or in addition to) AChE will allow for potential identification of the analyte based on different specificities/sensitivities of the enzyme. Enzymes such as OPH, which are not readily available, may be difficult to obtain in large quantities the supply of AChE is often limited perhaps due to the capture of electric eels, while proteins such as BChE (from horse blood) and carboxypeptidase (pancreas) are more readily available from slaughterhouses. 

Sensor systems based on the reversible, competitive inhibition of AChE and BChE by monosulfonate tetraphenyl porphyrin (TPPSi) were developed. TPPSi (350 iM in 50 mM pH 7 NaPi with 25% edianol) was applied to surfaces of immobilized enzymes and allowed to interact for 20 min before rinsing the excess solution off with excess buffer (50 mM NaPi pH 7). TPPSi was found to be a competitive inhibitor of cholinesterase activity for both AChE and BChE 12, 14, 15). The absorbance spectrum was unique for the AChE-TPPS complex (TAC) as compared to that of the BChE-TPPSi complex (TBC) with characteristic peaks at 446 nm for TAC and 412 nm for TBC. When TPPSi was applied to a siuface bearing both AChE and BChE (TABC), the characteristic peaks for both TAC and TBC were observed in the absorbance spectrum. 

Kulys, J. and D Costa, E.J. (1991) Printed amperometric sensor based on TCNQ and cholinesterase. Bt oieni. Bioelectron., 6, 109-115. 

A piezoelectric biosensor, for the detection of several organophosphorus pesticides was developed (Halamek et al., 2005). The sensor was based on the immobilization of a reversible inhibitor of cholinesterase on the surface of the sensor. The binding of AChE to this inhibitor was monitored with a mass-sensitive piezoelectric quartz crystal. In the presence of an inhibiting substance in the sample, the binding of the enzyme to the immobilized compound was reduced, and the decrease of mass change was proportional to the concentration of the analyte in the sample. This sensor was applied to the determination of pesticides in river water samples. 

Kulys J, D Costa EJ (1991) Printed amperometric sensors based rai TCNQ and cholinesterase. Biosens Bioelectron 6 109-115... 

Stoytcheva M, Zlatev R, Valdez B, Magnin JP, Velkova Z (2006) Electrochemical sensor based on Arthrobacter globiformis for cholinesterase activity determination. Biosens Bioelectron 22(l) l-9. doi 10.1016/j.bios.2005.11.013... 

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