Microelectrode system

Details Microelectrode system Microelectrode system

2001-05-21

2004-11-02

Noguerda, Alex (Department: 1753)

Chemistry: electrical and wave energy

Apparatus

Electrolytic

C204S600000, C204S612000, C204S403010, C204S409000, C204S424000, C324S448000, C324S449000

Reexamination Certificate

active

06811663

ABSTRACT:

The present invention relates to an electrode system, and particularly to a microelectrode system suitable for use in preparative and analytical chemistry.
Microelectrode systems are used extensively in research and are so named because their dimensions are on the micrometre scale. Such microelectrode systems provide very high field gradients and diffusion characteristics due to their small size. In addition, these types of microelectrode systems have found some limited commercial utility in biomedical applications and are typically used in, for example, blood gas analysis.
Reliable operation of microelectrode systems for preparative electrochemistry and electroanalytical techniques depends critically upon their geometry and the reproducibility of their manufacture. The performance of such a system generally improves as the dimensions of the system are reduced which is why microelectrode and even nanometre scale microelectrode systems are often desirable.
A disadvantage of known microelectrode systems of this type is that the reproducibility and reliability of the fabrication process and the geometries which may be adopted become more limited as the scale is reduced.
The present invention seeks to provide an improved microelectrode system which is more straightforwardly and reproducibly manufactured irrespective of dimensionality.
Thus viewed from one aspect the present invention provides a microelectrode system comprising a laminated structure having at least one conducting layer capable of acting as an electrode, at least one dielectric layer, an aperture formed in the laminated structure, and contact means for allowing electrical contact with at least one conducting layer.
As the dimensions of the microelectrode system of the invention are extremely small, the fields generated within the laminated structure are exceptional and enable highly efficient measurement and/or modification of materials entering into or passing through the system. The laminated structure is simple to manufacture to extremely high tolerances. In addition, the structure has extremely low dead volume thereby considerably simplifying physical sampling regimes.
The aperture may be in the form of a hole which extends through the laminated structure and is open at both ends. Alternatively, the aperture may be in the form of a well having an open end and an opposite end being closed to form a well bottom. In both embodiments, the internal wall of the hole or well formed in the microelectrode system may be uniform (eg substantially tubular) or non-uniform to provide non-uniform fields if desired. Materials may be passed into or through the laminated structure (via the aperture) where inter alia synthesis, analysis or sequencing as desired takes place.
The microelectrode system of the invention may comprise a plurality of apertures (eg holes or wells) formed within the laminated structure and spaced apart from one another. Each hole or well may be individually addressable, in which case each hole or well may have a different function. Alternatively, groups of holes or wells (or the totality of the holes or wells) in a structure may be addressed in parallel thereby enabling amplification of signals and parallel material processing. This latter system may be suitable for larger scale synthetic applications.
In one embodiment, the microelectrode system comprises at least one pair of substantially collinear wells having a common closed end. Particularly preferably, the microelectrode system comprises a plurality of such pairs.
At least one conducting layer of the microelectrode system of the invention acts as an electrode on the internal wall of the hole or well. The or each electrode may be treated to provide appropriate functionality (eg pH measurement or surface treatment for electro-catalysis) by known chemical and/or electrochemical and/or physical modification techniques.
The laminated structure may comprise a plurality of conducting and a plurality of dielectric layers. Preferably consecutive conducting layers are separated, by dielectric layers. Particularly preferably, a dielectric layer is uppermost in the laminated structure. In one embodiment, the laminated structure preferably comprises three conducting layers. Electrical fields are generated between the layers forming the laminated structure and within the aperture to provide the desired conditions.
Typically, the electrodes are formed from a noble metal, preferably gold. Gold may be sputtered onto a polymer which is capable of acting both as the mechanical support and as the dielectric layer. Any form of polymer or other dielectric material which is capable of acting as a support may be used such as for example polyethylenetetraphthalate (PET). Other specialised materials such as ion exchange polymers (eg cation doped polystyrene sulphonate) may be used for specialised applications.
Advantageously, the or each dielectric layer is made from a rubbery material. A suitable material is a polymer which swells when molecules of (for example) water enter the solid state matrix. During use of the microelectrode system, the rubbery dielectric layers separating pairs of conducting layers swell thereby changing the inter-electrode distance. Thus, the interspaced electrodes may be interrogated to determine the degree of swelling of the dielectric layers as a function of the measured resistance.
In more complex systems, material may be grown between the or each conducting layer and the or each rubbery dielectric layer, and the stress placed on the material as a consequence of the swelling of the or each dielectric layer may be measured.
A reagent loaded or functionalised dielectric layer may be used to provide additional functionality by providing ions or other materials to ensure the reproducible behaviour of subsequent systems within the structure. Ions may be conveniently provided by ion exchange resin materials. Other matrices could be employed to provide co-factors for biosensors, etc.
A specialised dielectric layer may also be used. The specialised layer may be in the form of an ion exchange resin, gel or solid electrolyte. In such a system, mass transport from one lateral region of the structure to another may be effected by inter alia osmosis, electro-osmosis, electrophoresis, electrochromatography or ion migration. Reverse flow and counter current techniques may be employed to effect changes in process flows including inter alia deionisation.
The laminated structure may be built on silicon. This has the advantage of being optically flat. Alternatively, the laminated structure may be built on a polymeric material (eg a polymeric material comprising one or more polymers).
The layers forming the laminated structure may be laid down using any one of a number of known techniques including casting, spinning, sputtering or, vapour deposition methods. The aperture may be mechanically or chemically introduced into the laminated structure. Advantageously, a micron gauge wire made of (for example) silver may be introduced into the laminated structure which wire may be etched out once the laminar structure has been completed. Alternatively, lithographic techniques or physical techniques such as laser oblation and neutron annihilation may be used. It is possible to produce highly uniform electrode layers with precise separations using such techniques allowing highly reproducible functional structures to be achieved.
The microelectrode system of the invention has many applications. For example, it may be used in the deionisation of a solution positioned on one side of a membrane forming the closed end of a well. In such a case, ions may be pumped through the microelectrode system as a consequence of a potential difference applied to electrodes on either side of the common well bottom. In such a case, the well bottom may be conveniently formed from an ion exchange material. The microelectrode may also be used in preparative electrochemistry, electroanalysis and chromatography or other separation techniques. It may also be used as a sensor.
Where the aperture is in t

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