Electrode microelectrode arrays

Flexible PI electrode microelectrode arrays have been developed for electric potential probing for in vivo applications. Implantable micro-... 

Rexible PI electrode microelectrode arrays have been developed for electric potential probing for in vivo applications [112], Implantable microelectrodes can be used to record neuronal action potentials or local field potentials from within the brain. The PI arrays consist of alternating layers of PI and platinum. The devices are fabricated by reactive ion etching. 

Porous electrodes, partially blocked electrodes, microelectrode arrays, electrodes made of composite materials, some modified electrodes and electrodes with adsorbed species are spatially heterogeneous in the electrochemical sense. The simulation of non-Cottrellian electrode responses at such surfaces is challenging both because of the surface variation and... 

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.

Both microstructured layer electrodes and microelectrode arrays have... 

Armstrong FA, Bond AM, Buchi FN, Hanmett A, Hill HAO, Lannon AM, Lettington OC, Zoski CG. 1993. Electrocatalytic reduction of hydrogen-peroxide at a stationary pyrol3ftic-graphite electrode surface in the presence of cytochrome-c peroxidase— A description based on a microelectrode array model for adsorbed enzyme molecules. Analyst 118 973-978. 

FIGURE 10.7 A thin film planar pH microelectrode array with 16 sputtered IrOx electrodes in a 4 X 4 arrangement. The needle type pH electrode as a control can be seen on the upper left comer of the array. (Reproduced from [19], with permission from the Electrochemical Society, Inc.)... 

In the case of a single electrode, however, the decrease of its dimensions requires the measurement of very low currents. To overcome this problem it is convenient to use microelectrode arrays [136, 137], Despite the fact that in such arrays microelectrodes are electronically connected to each other, analytical properties of such assemblies are advantageous over those of a conventional macro-electrode [138, 139],... 

Preparation of Microelectrode Arrays. The microelectrode arrays used in the work were arrays of microelectrodes each 80 pm long, 2.3pm wide and 0.1 pm thick and 3paced 1.7 pm apart. Fabrication and encapsulation of the microelectrode arrays has been described previously.<14.15.21-22) Prior to use, arrays of microelectrodes were cleaned by an rf 02 plasma etch to remove residual photoresist, followed by cycling the potential of each electrode between -1.5 V... 

Preparation and Electrochemical Behavior of Microelectrodes Modified with Poly(I). A microelectrode array consisting of eight Pt microelectrodes is cleaned and platinized as described in the Experimental Section. Poly(I) is deposited on the platinized microelectrode array by scanning the potential of the electrode(s) from 0 V to 1.5 V vs. Ag+/Ag in a solution of 0.2 MX in CH3CN/O.I M [U-BU4N]PFg. The resulting array is illustrated in Scheme I. The... 

Figure 3. Cyclic voltammetry of adjacent electrodes of a poly(I)-coated microelectrode array driven individually and together at 200 mV/s in the region of the oxidative potential of polythiophene in CH3CN/O.I II [11-BU4N] PFg.

The physical approach uses alternating current (ac-) dielectrophoresis to separate metallic and semiconducting SWCNTs in a single step without the need for chemical modifications [101]. The difference in dielectric constant between the two types of SWCNTs results in an opposite movement along an electric field gradient between two electrodes. This leads to the deposition of metallic nanotubes on the microelectrode array, while semiconducting CNTs remain in the solution and are flushed out of the system. Drawbacks of this separation technique are the formation of mixed bundles of CNTs due to insufficient dispersion and difficulties in up-scaling the process [102]. 

An optically transparent, porous platinum film has been produced by photoelectrodeposition on an InP semiconductor substrate [15], Polyester sheet covered with a thin film of sputtered gold has also proved suitable as an OTE [71]. When overcoated with a layer of Ti02, these electrodes exhibited electrochemical behavior consistent with a microelectrode array, including cyclic voltammetric current plateaus instead of clearly defined peaks, although this feature was not recognized at the time [71]. 

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. 

Fig. 24.4. Amperometric enzyme microelectrode array responses to acetylcholine between the concentration range 0-5 mM (n — 3, S.D. < + 10%). Inset shows a typical current transient response for an AChE electrode when exposed to 2.5 mM acetylthiocholine chloride.

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]). 

Another important future direction is in the use of microelectrodes and microelectrode arrays. They are often easier to manipulate by the inexperienced, and instrumentation is simpler. They can be used in highly resistive dirty media where conventional electrodes may be unuseable and are able to probe localized concentrations. Composite electrodes42, of which carbon paste is an example, if conveniently prepared, can act as microelectrode assemblies. In a more general sense, lithographic and... 

One of the inherent problems associated with any heterogeneous technique such as voltammetry is the reproducibility of the properties and nature of an electrode surface. Traditionally, studies in which this was crucial utilized a hanging mercury drop, or dropping mercury electrode which ensured a continuously renewable surface. Cardwell et al. (1996) have described improved techniques for polishing electrodes which will go some way towards providing more reproducible electrode surfaces. Reproducibility may be assisted by the development of disposable electrodes (for example, Wang and Chen, 1994) that have developed disposable enzyme microelectrode array strips for glucose and lactate detection. 

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