Microfabricated microelectrodes

Microfabrication and micromachining techniques have also been used in the manufacture of electrochemical sensors. This includes po and pco sensors. Zhou et al [9] describe an amperometric CO2 sensor using microfabricated microelectrodes. In this development, silicon-based microfabrication techniques are used, including photolithographic reduction, chemical etching, and thin-film metallization. In Zhou s study, the working electrodes are in the shape of a microdisk, 10 pm in diameter, and are connected in parallel. In recent years, silicon-based microfabrication techniques have been applied to the development of microelectrochemical sensors for blood gases, i.e. P02. Pcoj and pH measurements. 

M. L. Kovarik, M.W. Li and R.S. Martin, Integration of a carbon microelectrode with a microfabricated palladium decoupler for use in microchip capillary electrophoresis/ electrochemistry, Electrophoresis, 26 (2005) 202-210. 

The actual retina contact structure incorporates 12 or 24 independent electrodes, respectively. The electrodes were arranged concentrically to minimize the electrical stray field during stimulation. We established the microfabrication process for double metallization layers needed to obtain concentric microelectrodes. In a temper step, the electrodes were formed into a convex shape according to the curvature of the eye. The generation of convex shapes was possible since the stimulator was designed in concentric rings interconnected by s-shaped bridges (Fig. 26). 

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. 

At present a few studies of nanofibers and nanombes are focused on CNS drug delivery. One study evaluated electrospun nanofibers of a degradable polymer, PLGA, loaded with antiinflammatory agent, dexamethasone, for neural prosthetic applications (Abidian and Martin, 2005). A conducting polymer, poly(3,4-ethylenedioxythiophene), was deposited to the nano-fiber surface and the coated nanofibers were then mounted on the microfabricated neural microelectrodes, which were implanted into brain. The drug was released by electrical stimulation that induced a local dilation of the coat and increased permeability. 

Selection of fertilizable oocytes is one of the most important issues in in vitro fertilization (IVF) process. To date, the oocyte selection has been manually conducted by a skillful expert with a labor-intensive and time-consuming process. Recently, a new method for DEP-based separation of normal oocytes has been demonstrated using a microelectrode device [45]. The normal oocytes showed higher DEP velocity compared to the abnormal ones, which were cultured without medium for 3 days. This result shows that the DEP characteristics of oocytes can be a new criterion for selecting healthy oocytes in IVF. However, the conventional separation method based on the microfabricated electrodes has some limitation such as difficulty of manipulating samples before and after the selection processes. To develop a fully-automated system for the discrimination of normal oocytes for IVF, an ECD-based optoelectrofiuidic platform, which allows the programmable cell manipulation based on the optically induced DEP and the image-driven virtual electrodes, has been utilized [26]. 

A microbiosensing device fabricated by assembling an enzyme-embodied microelectrode with a counter electrode and a reference electrode was applied to the real time determination of a trace droplet of glucose sample. The mlcrodevice demonstrated unique properties such as real time response, independence of sample volume, and no need for sample mixing by the combination of a microfabricated biosensing device with pulse voltammetry. 

The microfabrication of electrode arrays built with silicon micromachining techniques illustrates an positive approach towards future Cl electrode array development in respect to the traditional manufacturing method used now days. Also lithography and MEMS technology facilitates the addition of enhanced functionality to the microelectrode arrays. There is, however, still a long way to go until these devices can be used in real Cochlear Implants. The fabrication possibilities and characterization of different CMOS compatible metals (Ti, TiN and Al) provides a strong base to go ahead with further research in this direction. In our electrical tests done we conclude that TiN is able to withstand a high current density 2.8, while aluminium failed... 

Tab. 1 Microfabrication techniques that can be used to produce microelectrode arrays and microchemical sensors and biosensors...

Al Mamun NH, Dutta P (2006). Patterning of platinum microelectrodes in polymeric microfluidic chips. Journal of Microlithography Microfabrication and Microsystems. 5(3) 039701-1 to 039701-6... 

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