Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2001-06-08
2003-06-24
Nguyen, Nam (Department: 1753)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S403110
Reexamination Certificate
active
06582573
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrochemical test device suitable for determining the presence or concentration of chemical and biochemical components (analytes) in aqueous fluid samples and body fluids such as whole blood or interstitial fluid. Additionally, this invention relates to a method of using such test devices for determining the presence or concentration of an analyte and to processes for preparing such a test devices.
2. State of the Art
Medical studies have demonstrated that the incidence of serious complications resulting from diabetes, such as vision loss and kidney malfunction, can be significantly reduced by careful control of blood glucose levels. As a result, millions of diabetics use glucose testing devices daily to monitor their blood glucose concentrations. Additionally, a wide variety of other blood testing devices are used to determine the presence or concentration of other analytes, such as alcohol or cholesterol, in aqueous samples, such as blood.
Such blood testing devices typically employ either a dry chemistry reagent system or an electrochemical method to test for the analyte in the fluid sample. In recent years, electrochemical testing systems have become increasingly popular due to their small size and ease of use. Such electrochemical testing systems typically use electrochemistry to create an electrical signal which correlates to the concentration of the analyte in the aqueous sample.
Numerous electrochemical testing systems and related methods are known in the art. For example, European Patent Publication No. 0 255 291 B1, to Birch et al., describes methods and an apparatus for making electrochemical measurements, in particular but not exclusively for the purpose of carrying out microchemical testing on small liquid samples of biological, e.g. of clinical, origin.
European Patent Publication No. 0 351 891 B1, to Hill et al., teaches a method of making an electrochemical sensor by printing. The sensor is used to detect, measure or monitor a given dissolved substrate in a mixture of dissolved substrates, most specifically glucose in body fluid.
U.S. Pat. No. 5,391,250, to Cheney II et al., teaches a method of fabricating thin film electrochemical sensors for use in measuring subcutaneous or transdermal glucose. Fabrication of the sensors comprises placing a thin film base layer of insulating material onto a rigid substrate. Conductor elements for the sensors are formed on the base layer using contact mask photolithography and a thin film cover layer.
U.S. Pat. No. 5,437,999, to Diebold et al., teaches a method of fabricating thin film electrochemical devices which are suitable for biological applications using photolithography to define the electrode areas. The disclosures of each of the above patent specifications are incorporated herein by reference in their entirety.
An excellent reference on materials and process for fabricating electronic components is Charles A. Harper, Handbook of Materials and Processes for Electronics, 1984, Library of Congress card number 76-95803. It provides detail process information on thick film, thin film and photo resist processes.
Existing electrochemical testing systems, however, have certain limitations from the perspective of the end user or the manufacturer. For example, some electrochemical testing systems are difficult or costly to manufacture. As a result, such devices are too expensive to be used on a daily basis by, for example, diabetics. Other electrochemical testing systems are not sufficiently accurate to detect certain analytes at very low concentrations or to give reliable measurements of the analyte's concentration. Additionally, many electrochemical devices are too large to be easily carried by those needing to test their blood on a regular basis throughout the day. Thus, a need exists for improved electrochemical test devices.
SUMMARY OF THE INVENTION
The present invention utilizes amorphous semiconductor applied with thin film manufacturing techniques and membranes which have a skin on each planar surface to provide an electrochemical test device suitable for determining the presence or concentration of analytes in aqueous fluid samples. By using amorphous semiconductor materials applied with film manufacturing techniques and dual skin membranes, uniform electrochemical test devices having well-defined reproducible electrode areas can be manufactured economically.
In particular, the test devices of this invention have very uniform surface areas which reduce the variability of the electrochemical test. In this regard, it has been found that the surface area of the electrodes and the accuracy of applying the reagent are critical to producing an accurate test. If the surface area is not consistent from test to test then each of the test devices must be individually calibrated to insure accurate readings. The test devices of the present invention permit highly accurate electrochemical analyte measurements to be performed on very small aqueous fluid samples without the need for individual calibration of each test device. The present inventions provide for the accurate reproduction of the test devices by using controlled deposition methods, such as sputtering or vapor deposition and smooth skin membranes to form the electrodes with consistent size and surface morphology from device to device in continuous production. These devices can also be readily manufactured due to the lower cost and the flexible nature of the amorphous semiconductor materials which facilitates production by continuous roll processing versus the step and repeat printing methods currently employed. The ability to use continuous processing to fabricate the device, such as continuous processes utilizing continuous roll coating, continuous roll sputtering, continuous systems utilizing contact masks, results in high volume manufacturing capability and substantial cost reductions over the step and repeat processes. Additionally, the amorphous nature of the conductors electrodes and constructed and used according to this invention eliminates problems found in prior test devices which utilize conventional conductor and semiconductor materials, which are crystalline in nature or are noble metals and, as a result, require flat and rigid substrates to prevent cracking during manufacture, distribution or use. The membrane in the present invention is the earlier for the indicating reagent and forms the surface for the electrode formation. The membrane comprises the matrix in which the reagent is carried or impregnated and comprises the two exterior skin surfaces on which the electrodes are placed. The skin surfaces can be smooth skin suitable for carrying the electrodes and can be porous to pass the aqueous fluid samples or can have pores sized to screen or block selected components from aqueous fluid sample, such as red blood cells in a blood sample.
Dry electrochemical test devices fall into two primary configurations. The first configuration utilizes two electrodes, i.e., a working electrode and a counter electrode. The second configuration utilizes three electrodes, i.e., a working electrode, a counter electrode and a reference electrode. The use of the reference electrode and a reference material provides a fixed reference for the test. The test devices of the present invention are well suited for a two electrode system however, a contact mask could be employed during sputtering to create a surface with two electrodes.
Accordingly, in one of its aspects, the present invention provides an electrochemical test device for determining the presence or concentration of an analyte in an aqueous fluid sample, said electrochemical test device comprising:
(a) a nonconductive surface;
(b) a working electrode comprising an amorphous semiconductor material affixed to the non-conductive surface of a double skin membrane, said working electrode having an first electrode area, a first lead and a first contact pad;
(c) a counter electrode comprising an amorphous semiconductor material
Douglas Joel S.
Hasker David A.
Priest John H.
Roe Jeffrey N.
Amira Medical
Nguyen Nam
Noguerola Alex
Woodward, Emhardt, Moriarty, McNett & Henry LLP
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