Electrochemical assays

Berger, M., Anselmino, C., Mouret, J.F. and Cadet, J. (1990). H performance liquid chromatography-electrochemical assay for monitoring the formation of 8-oxo-7,8-dihydro-adenine and its related 2 -deoxyribonucleoside. J. Liquid Chromatog. 13, 929-940. 

These results, completely analogous to our electrochemical assays, illustrate how protein binding sensitively modulates long-range DNA-mediated CT in a manner that is highly dependent on the specific DNA-protein interactions involved. Consequently, we have recently applied this chemistry as a... 

Due to their response mechanism the polyion-selective electrodes are not sensitive to the small fragments of polyionic macromolecules. Thus, if an enzyme cleaves the polyionic molecule these sensors can be used for detection of enzyme activity. Polycation protamine is rich in arginine residues that make it a suitable substrate for protease-sensitive electrochemical assays. Real-time detection of trypsine activity was demonstrated with the protamine-selective electrode as a detector [38],... 

L.-C. Chang, M.E. Meyerhoff, and V.C. Yang, Electrochemical assay of plasminogen activators in plasma using polyion-sensitive membrane electrode detection. Anal. Biochem. 276, 8-12 (1999). 

Another method is explored with gene expression-based biosensors [19] for Cd measurement. A Cd-responsive promoter from E. coli is fused to a promoterless lacZ gene and monitored with an electrochemical assay of /J-galac-tosidase activity. The expected detection limit is about 0.1 mg L 1 with a response of a few minutes. As for stripping voltammetry, no real tests have been carried out for wastewater. However, biosensors can be considered as a promising technique for wastewater monitoring. 

W. Qin, W. Zhang, K. P. Xiao, and M. E. Meyerhoff, Enhanced Sensitivity Electrochemical Assay of Low-Molecular-Weight Heparins Using Rotating Polyion-Sensitive Membrane Electrodes, Anal. Bioanal. Chem. 2003, 377, 929. 

Clark, J.B. 1992. Electrochemical assays The oxygen electrode. In Enzyme Assays A Practical Approach (R. Eisenthal and M.J. Danson, eds.) pp. 181-190. IRL Press, Oxford. 

K.C. Honeychurch, J.P. Hart, P.R.J. Pritchard, S.J. Hawkins and N.M. Ratcliffe, Development of an electrochemical assay for 2,6-dinitrotolu-ene, based on a screen-printed carbon electrode, and its potential application in bioanalysis, occupational and public health, Biosens. Bioelectron., 19 (2003) 305-312. 

The bar charts in Figs. 27.5 and 27.6 illustrate particle size distribution before and after samples centrifugation. After centrifugation an average size of silver particles in the samples, containing 10, 15 and 50 pg/ml of protein A, is close to 5-8 nm. In the samples, containing protein in concentrations 70 or 100 pg/ml the prevailing Ag particle size is 2-3 nm. The results of electrochemical assay demonstrate that the... 

Samples in — 55) fortified at different levels (4, 2, 1, and 0.5 mg/kg) were extracted and analyzed with the proposed electrochemical assay using both eeAChE and rAChE. For eeAChE, the recovery for di-chlorvos-spiked samples ranged between 74 and 78%. The incomplete recovery may be due to concurrent causes, such as the use of whole kernels as sample, water-based extraction solvent, and adsorption... 

Pirimiphos-methyl determination in durum wheat samples The electrochemical assay for the detection of AChE inhibitors outlined above has been optimized for the detection of pirimiphos methyl-pirimiphos-methyl in durum wheat. Pirimiphos methyl is a phosphot-ionate insecticide and therefore it requires to be transformed in the corresponding oxo-form to act as an effective AChE inhibitor, in fact it did not show inhibition of AChE in a concentration range 50-5000 ng/ mL (data not shown). 

Electrochemical assays of nucleic acids based on DNA hybridisation have received considerable attention [34,57-60]. DNA hybridisation biosensors are a very attractive topic in the clinical diagnostics of inherited diseases and the rapid detection of infectious microorganisms. 

Polish the GCE using diamond spray (particle size 1 pm) before every electrochemical assay. After polishing, rinse the electrode thoroughly with Milli-Q water for 30 s, then sonicate for lmin in an ultrasound bath and again rinse with water. After this mechanical treatment, place the GCE in pH 4.5 0.1 M acetate buffer electrolyte and record various DP voltammograms until a steady-state baseline voltammogram is obtained. This procedure is fundamental in order to obtain reproducible experimental results. 

Enzyme biosensors containing pol3mieric electron transfer systems have been studied for more than a decade. One of the earlier systems was first reported by Degani and Heller [1,2] using electron transfer relays to improve electrochemical assay of substrates. Soon after Okamoto, Skotheim, Hale and co-workers reported various flexible polymeric electron transfer systems appUed to amperometric enz5une biosensors [3-16], Heller and co-workers further developed a concept of wired amperometric enzyme electrodes [17—27] to increase sensor accuracy and stability. 

Standardization of developed assays The developed electrochemical assays should be easily standardized, or have a potential for later standardization. 

This technique was also used to monitor the effects of applied electric fields on hybridization and dchybridization not surprisingly, it was found that even small fields can significantly accelerate these processes. Mismatched sequences were particularly susceptible to potential-induced dehybridization, an effect that is potentially useful in discriminating between closely related sequences. As similar electric fields are involved in electrochemical assays, the effects of these fields on the DNA-film structure must be considered in the design and interpretation of DNA detection experiments. 

An alternative approach for utilizing DNA thin films for electrochemical sensors involves using redox-active probe molecules intercalated into the Ji-stack. Fig 5-lb. This approach has been successfully employed in the design of electrochemical assays for hybridization,single-base mismatches, and chemical modifications and lesions within duplex DNA. It has also provided provocative experimental results regarding charge transport through the double helix. ... 

D.S. Goldstein, Modifled sample preparation for high-performance liquid chromatographic-electrochemical assay of urinary catecholamines, J. Chromatogr, 275, 174—177 (1983). 

Centi, S., Tombelli, S., Minunni, M., Mas-cini, M. (2007). Aptamer-based detection of plasma proteins by an electrochemical assay... 

Nanoparticles in general and gold nanoparticles particularly offer attractive properties to act as DNA tags (11). Their sensitivity, long life-time along with multiplexing capability have led to an extensive applications in electrochemical assays in recent years... 

Kirschbaum, J. Perlman, S. Analysis of captopril and hydrochlorothiazide combination tablet formulations by liquid chromatography. J.Pharm.Sci., 1984, 73, 686-687 Perrett, D. Rudge, S.R. Drury, P.L. Determination of captopril by an improved high-performance liquid chromatography-electrochemical assay. Biochem.Soc.Trans., 1984,12, 1059-1060 Toyooka, T. Imai, K. Kawahara, Y. Determination of toted captopril in dog plasma by HPLC after prelabeling with ammonium 7-fluorobenzo-2-oxa-l,3-diazole-4-sulfonate (SBD-F). J.Pharm. Biomed.Anal., 1984, 2, 473-479 [derivatization]... 

The attachment of the ferrocene groups to small molecules has been used in two main classes of biosensor in the first, the conjugate is an enzyme substrate such that a shift in its redox potential occurs following enzymatic modification. An example is ferrocenylethyl phosphate (Figure 9) that facilitates the electrochemical assay of alkaline phosphatase, a common enzyme label for immunoassays. The redox potential of the alcohol product is lower than the phosphate ester and hence by poising the potential, the product can be selectively measured and so the alkaline phosphatase activity measured. The sensitivity of this method was further enhanced by the use of stripping voltammetry to detect the product. ... 

Electrochemical assays for therapeutic drugs, like paracetamol or acetyl-salicylate have been described [35]. Urea can be assayed potentiometrically by a H sensitive ISFET with a Si02 gate insulator covered by a SijN4 Him to which urease (EC 3.5.1.5) is covalently attached [36]. 

An aptamer-based sandwich assay with electrochemical detection for thrombin analysis in complex matrixes using a target-capturing step by aptamer-functionalized magnetic beads was recently reported (Centi et al., 2007). The aptamer-sensing layers were fabricated on a surface of screen-printed electrodes. The high sensitivity of this sensor was demonstrated in the analysis of thrombin in buffer, spiked serum, and plasma. The concentrations detected by the electrochemical assay were in agreement with simulation software that mimics the kinetics of thrombin formation. 

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