Electrochemical sensors are known which are used in the analysis of liquid samples. Such sensors are used in the analysis of blood or other biological fluids.
For example, blood sugar analyzers analyze the blood sugar content or glucose concentration of a blood specimen by supplying a blood specimen to a fixed enzyme membrane to cause a chemical reaction. A reaction current is then generated proportional to the amount of the blood sugar in the blood specimen.
A person may also become infected with a disease, which will result in the person""s blood containing measurable levels of an antigen specific to the disease. Immunodiagnostic tests are conducted on a sample of the infected person""s blood whereby antibodies specific to the disease condition are contacted with the blood sample. If an antigen-antibody reaction occurs, the antigen is confirmed to be present. Of course, the reaction may be conducted in the reverse, by contacting an antigen with a sample containing the suspected antibody. While a variety of techniques have been developed to determine the result of the test (enzyme immunoassay, immunofluoresence, radioimmunoassay, etc.). It has also become appropriate to employ electrical immunoassay techniques whereby the electrical properties of the fluid sample are changed due to the antigen-antibody reaction. Alternatively, one immunoreactant can be labelled with an electroactive substance, with the extent of the reaction determining the level of the electrical property to be observed.
The above techniques, as well as several others, are described in U.S. Pat. No. 4,420,564 (blood sugar analyzer); U.S. Pat. No. 4,511,659 (liquid chromatograph with electrochemical detector); U.S. Pat. No. 4,655,880 (sensor apparatus using oxidase); U.S. Pat. No. 5,137,827 (diagnostic element for electrical detection of binding reaction); U.S. Pat. No. 5,250,439 (conductive sensor in diagnostic assay); U.S. Pat. No. 5,385,846 (biosensor for hematocrit determination); U.S. Pat. No. 5,512,489 (microelectrodes and amperometric assay); U.S. Pat. No. 5,571,401 (sensor arrays for detecting analytes in fluids); U.S. Pat. No. 5,739,039 (microelectrodes and amperometric assays); U.S. Pat. No. 5,788,833 (sensors for detecting analytes in fluids); U.S. Pat. No. 5,789,255 (blood glucose strips having reduced sensitivity to hematocrit); U.S. Pat. No. 5,911,872 (sensors for detecting analytes in fluids); U.S. Pat. No. 5,916,156 (electrochemical sensors having improved selectivity and enhanced sensitivity); U.S. Pat. No. 6,093,308 (sensors for detecting analytes in fluids); U.S. Pat. No. 6,210,972 (characterization of flowing dispersions); and U.S. Pat. No. 6,331,244 (sensors for detecting analytes in fluids).
Electrochemical sensors that require an ultra-small sample volume are of interest for those applications where the sample is difficult to produce or where the sample is recovered by invasive means which may involve the undesirable infliction of pain (such as penetration of the skin with a pointed object). Currently, it is believed that the smallest volume of liquid sample which can be analyzed is approximately 300 nL in size. Such devices are inherently planar in configuration, and draw a liquid sample into a single, large lateral flow transport channel. The configuration of the channel is based on several parameters, including material thickness, printed feature size and channel orientation. It is, however, desirable to produce an electrochemical sensor which enables liquid samples of much smaller volume to be analyzed.
It is accordingly an object of the present invention to provide an electrochemical sensor which may be used to perform small volume analysis of liquid samples such as biological fluids.
In accordance with the present invention, there is thus provided an electrochemical sensor comprised of a thin sheet or film having at least one through-hole provided therein, said thin sheet or film having first and second opposing surfaces, at least a portion of said opposing surfaces being coated with a conductive coating which extends into said at least one through-hole, each said conductive coating extending partially into said at least one through-hole from each opposing surface whereby each said conductive coating terminates within said at least one through-hole at a point spaced from the terminus of the opposing conductive coating which extends into said at least one through-hole, whereby said conductive coatings in said at least one through-hole are separated by an uncoated surface of said at least one through-hole.