Microelectrodes multiple

W.E. Morf and N.F. de Rooij, Performance of amperometric sensors based on multiple microelectrode arrays. Sens. Actuators B. 44, 538-541 (1997). 

Recently, both hirsutine (85) and dihydrocorynantheine (86) were found to be active when the effects of these compounds on the action potentials of sino-atrial node, atrium and ventricle tissues were studied with standard microelectrode techniques [65]. In sino-atrial node preparations, both compounds concentration-dependently increased cycle length, decreased the slope of the pacemaker depolarization, decreased the maximum rate of rise and prolonged action potential duration. Thus, it was for the first time shown that hirsutine and dihydrocorynantheine have direct inhibitory effects on the cardiac pacemaker. In atrial and ventricular preparations, both compounds concentration-dependently decreased the maximum rate of rise and prolonged action potential duration. Although stereochemically different, these two alkaloids exhibited no difference in their effects on various myocardial action potential parameters. Dihydrocorynantheine also displays potent a-adrenoceptor blocking activity, while hirsutine is inactive [66]. Experiments with ion channels indicate that the mechanisms for these two phenomena probably differ. The direct effects of hirsutine and dihydrocorynantheine on the action potential of cardiac muscle through inhibition of multiple ion channels may explain the negative chronotropic and antiarrhythmic activities of these two alkaloids. 

Microelectrode arrays containing AChE were also utilised within a flow injection system [40]. A system was developed where a sample was separated and flushed simultaneously through eight cells, each containing a screen-printed electrode and fitted with a separate bespoke mini-potentiostat (Fig. 15.3). This allowed multiple measurements to be made on a single water sample using multiple electrodes, each specific for a different pesticide due to inclusions of different AChE mutants in each of the electrodes. Pattern-recognition software could then be utilised to deduce the pesticide levels in a potentially complex sample. 

Hybride micro-FIA systems produced in silicon technology using oxygen microelectrodes and microcavities have been developed for measuring phosphate concentrations [96]. Multiple analyte biosensor arrays can also be realized using thin film and silicon technology. The so-called containment technology has been applied to immobilize enzymes in three dimensional cavities formed in silicon wafers to get fully process compatible biosensor devices [97] (Fig. 5). 

The detection of the current generated by reaction at the surface of (usually) carbon fiber or copper microelectrodes at a fixed voltage is capable of low detection limits for electroactive compounds using amperometry, Table 8.14. Several approaches that allow the full possibilities of multiple electrode and pulsed amperometric detection (established techniques in liquid chromatography (section 5.7.4)) have been proven for capillary electrophoresis [508,511]. These methods are not widely used, possibly due to a lack of commercial products and support. Potentiometric detection with polymer-coated wire microelectrodes containing relatively non-specific ion exchange ionophores was used for the detection of low-mass anions or cations [510,511]. 

It is clear from the literature review that the need continues to exist for a high throughput functional toxin detection system, which could detect and identify unknown or unexpected toxic chemicals in continuous long term experiments in field conditions. Microelectrode array recordings may show some promise in some specific fields as they are relatively more rugged, simpler and cheaper to implement than automated patch clamp devices. However, in addition to international validation studies, cell type selection and automated data analysis capabilities of multiple signals will be critical. 

Figure 5.4 All-diamond coplanar micro-and macroelectrodes, (a) Multiple microelectrode array formed from machining pillar structures in free-standing BDD, overgrowing with insulating diamond, and then polishing flat to reveal a coplanar structure. SEM side on view of cross-sectioned microelectrode array. (Taken from Ref. [50] with permission.) (b) Atomic Force Microscopy (AFM) topography image of one of the electrodes in the array the location of the BDD microdisk ultramicroelectrode is clearly visible. (Taken...

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