Polymer-based microelectrodes

Conducting polymers have already been well documented in conjunction with the classical ionophore-based solvent polymeric ion-selective membrane as an ion-to-electron transducer. This approach has been applied to both macro- and microelectrodes. However, with careful control of the optimisation process (i.e. ionic/electronic transport properties of the polymer), the doping of the polymer matrix with anion-recognition sites will ultimately allow selective anion recognition and ion-to-electron transduction to occur within the same molecule. This is obviously ideal and would allow for the production of durable microsensors, as conducting polymer-based electrodes, and due to the nature of their manufacture these are suited to miniaturisation. There are various examples of anion-selective sensors formed using this technique reported in the literature, some of which are listed below. 

Future work will focus on real three-dimensional electrodes that may slowly penetrate the superficial layer of the retina. We hope to improve the spatial selectivity of a stimulator structure and to lower the energy consumption during stimulation, when the microelectrode is in close proximity to the somata of the ganglion cells. A possible design of this structure is shown in Fig. 27. It demonstrates the design potentials that microfabrication of polymer based microstructure offer. 

Finally, Taguchi s group developed an integrated system for the detection of gases and volatile liquids [71]. The detection was based on changes in electrical resistance, which occurs when polymer-coated microelectrodes were exposed to the different samples. In this investigation, pH and sodium chloride were detected, and it is claimed that this approach may even be used to detect color for display device applications. This may lead to further development of an electronic eye. 

Figure 10.1 Atomic force microscopy (AFM) image of one 100-nm-wide polypyrrole wire that bridges the ends of two polypyrrole microelectrodes (size 9 pm x Wpm). (Reprinted with permission from Advanced Materials, Patterning of Conducting Polymers Based on a Random Copolymer Strategy Toward the Facile Fabrication of Nanosensors Exclusively Based on Polymers by B. Dong, D. Y. Zhong, L. F. Chi and FI. Fuchs, 17, 22, 2736-2741. Copyright (2005) Wiley-VCH)...

In contrast, polymer-based thin-film electrodes offer the possibility of creating a monolithic device, in which the microelectrodes and the flexible interconnect are fabricated as one structure. 

Fig. 6. Molecular transistor based on a microelectrode array. P is a polymer layer that can be switched conductive or nonconductive by the potential of the gate electrode (from ref.

This chapter focuses on the approach we followed for developing a novel electrochemical sensor platform based on disposable polymer microchips with integrated microelectrodes for signal transduction. It presents the development of the so-called Immuspeed technology, which is dedicated to quantitative immunoassays with reduced time-to-results as well as sample and reagent volumes. Prior to presenting the specific characteristics of Immuspeed, the basic principles integrated in this platform are first presented and illustrated with reference to... 

Figure 14.2.4 More complex modified electrode structures based on electroactive polymers, (a) Sandwich electrode (b) array electrode (c) microelectrode d, e) bilayer electrodes if) ion-gate electrode. [Reprinted with permission from C. E. D. Chidsey and R. W. Murray, Science, 231, 25 (1986), copyright 1986, American Association for the Advancement of Science.]...

The redox behavior of PVFc (VFc ) has been utilized in the construction of a microelectrochemical diode along with a redox-active viologen-based V,A -dibenzyl-4,4 -bipyridinium-based polymer (BPQ ). The polymers were coated upon microelectrodes and current was found to pass when the negative lead was attached to the (BPQ ) electrode and the positive lead was connected to the (VFc ) electrode. Thus, as the applied potential approached the difference in redox potentials of the two polymers, current flowed as shown in Equation (5a), and is favorable by p 0.9V. However, current does not flow if the applied potential is in the opposite sense as seen in Equation (5b), as it is disfavored by 0.9 V. The switching time of this diode, which is controlled by the time required to oxidize or reduce the polymers, was long in comparison with that of the solid-state diodes. ... 

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