Insulator electrode devices

#The present invention relates to hot electron-operated electrochemical reactors which are applied to carry out chemical reactions. The device comprises working electrode/electrodes which are coated according to the prior art with an electrically insulating layer, which enables to carry out non-conventional electrochemical redox reactions. Said electrode device has a wide area of applications as a chemical reactor, in analytical chemistry, and in biochemistry as a sensitive detector, in particular, with methods based on biorecognition, such as in clinical diagnostics.

#A considerable improvement over the active metal or semiconductor electrodes used to carry out different electrochemical reactions was provided by the publication WO 98/36266 (U.S. Pat. No. 6,251,690 Kulmala et al.). These so-called insulating film-coated electrodes can be applied to the generation of exceptional chemical reactions at high redox energy levels. When such electrode reactions are effected in the presence of certain organic or inorganic luminophores, light is generated. Whereas a variety of applications based on this phenomenon can be readily advised, one of the most evident one is the use of such a system as a sensitive detector in analytical chemistry as described in WO 98/36266.

#Many commercially important analytical methods require sensitive and specific detectors. The majority of such methods are based on the principle that the analytes are separated by their biological function and thereafter quantified using certain label substances. For instance, in the assays based on the biological properties of analytes, such as in immunoassays, the analyte (A) can be selectively captured from a solution upon a solid support with the aid of antibodies immobilized on the surface of the solid support, and the amount of (A) can be quantified using another antibody selectively binding with (A) and being labeled with a suitable marker substance. Such a marker substance can be, for instance, a radioactive isotope, an enzyme, a molecule that absorbs light or produces fluorescence or phosphorescence, certain metal chelates etc., which can be coupled with an antibody via chemical bonds. Alternatively, purified (A) can be labeled (A—L) and the amount of unlabeled (A) can be determined by antibodies immobilized on a solid support by exploiting a competitive reaction between (A—L) and analyte (A). DNA- and RNA-probing assays are based on analogous bioaffinity principles to those of immunoassays and can be performed along with related procedures. Also, other chemical and biochemical analysis methods can be based on analogous principles. Presently, there is an increasing need for multiparameter assays due to a growing demand to decrease the costs and/or increase the simplicity and accuracy of determinations. One solution to these problems is the use of label compounds which luminesce at different wavelengths. Various methods and strategies in immunoassays are described, e.g., in “The Immunoassay Handbook”, Edited by David Wild, Stockton Press Ltd., New York, 1994, pages 1-618.

#FIG. 1. (a) The figure presents a schematic measuring set-up for the use of insulator electrode devices in simple flow-through systems and circulated solution flow systems. (1) A channeled insulator electrode device, (2) peristaltic pump, (3) valve leading either to a waste chamber, (5) or circulation liquid chamber (4). (b) The figure displays a structure of a channeled insulator electrode device. The simplest device is composed of a single thin layer channel between planar thin insulating film-coated working electrode and planar metal or optically transparent counter electrode, such as ITO-coated glass electrode or conductive polymer coated plastic electrode. Normally, the working electrode has multiple small-diameter channels and the counter electrode has either a planar or a channeled structure. (6) Planar metal or optically transparent counter electrode, (7) insulator spacer (e.g. SU-8), (8) Insulating film-coated channeled working electrode. (c) A schematic diagram of a housing of flow-through insulator electrode devices which allows light detection from the device either by optical cable or by putting a photomultiplier tube window close to the flow-through device housing window. (10) Housing body, (11) Screwable housing cap to tighten the flow through device, (12) Optical window to allow light detection from the flow-through devices, (13) Inlet tubing, (14) Outlet tubing, (15) and (16) anode and cathode wires connected to a pulse generator. The contacts to the electrodes inside the housing have to be arranged differently depending on whether the working electrode chip or counter electrode is optically transparent. In the applications, in which the light detection was not needed, the optical window (12) allowed to see that no gas bubble problems etc. were occurring.

#FIG. 2. (a) a p-type Si-electrode grooved by sawing with 20 μm wide blade. (b) The bottom of a groove of the electrodes polished by isotropic etching as monitored by scanning electron microscope.

#FIG. 3. Decomposition of benzene in an insulator electrode device. The decay of benzene is monitored by absorbance at wavelength of 261 nm. Curve (a) displays the results obtained with a planar working electrode (single-channel device) and curve (b) those obtained with an electrode having 30 μm wide and 400 μm deep grooves (multi-channel device).

#The aim of the invention is the provision of methods and devices, with which novel electrochemical reactions are generated in specially constructed micropores or channels. The advantages of the present invention are illustrated by the electrochemical reactions of different types of luminescent label compounds. Such resulting luminescence can be commercially applied, for example, to the detection step of fast bioaffinity assays. One of the basic embodiments of the invention is the use of short diffusion distances of analytes and reagents provided by the design of high-surface area electrodes and miniaturized reaction and measuring cells. Other applications of the present invention includes various chemical reactors to be used in micro or macro scale.

#According to one embodiment, the invention concerns a method for electrical excitation of a label molecule, comprising at least partially immersing an insulating film-coated electrode in an electrolyte solution containing at least one label molecule; exciting said label molecule by an electrical pulse from said electrode, thereby producing an excited label; detecting luminescence emitted by said excited label; and quantifying the presence of the label based on the detected luminescence, wherein said electrode comprises an electrically conductive material and at least the portion of said electrode which is immersed in said solution is substantially covered with an electrically insulating film having a band gap equal to or greater than 5 eV; wherein the surface of the electrode is channeled to give at least a 1.5 times higher specific surface area of the electrode as compared to that of a corresponding non-channeled electrode.

#The invention also concerns a flow-through electrode device comprising an insulator electrode device as defined, the electrode comprising flow channels of a diameter of 10-500 μm and channel lengths of less than 10 mm, extending from one end of the electrode to the other end, the flow-through device additionally comprising an inlet flow-distributor for a sample liquid, for distributing the liquid into the separate flow channels of the electrode, and an outlet collector of the liquid from the electrode device, the device comprising means for detecting and measuring emitted light from all channels integrally or separately from each of, or from a group of channels.