Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2001-07-31
2004-07-27
Olsen, Kaj K. (Department: 1753)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S403120, C204S403140
Reexamination Certificate
active
06767441
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a biosensor that can be used for the quantification of a specific component or analyte in a liquid sample. Particularly, this invention relates to a new and improved biosensor and to a new and improved method of fabricating a biosensor for the quantification of a specific component or analyte in a liquid sample such as creatinine, creatine, glucose, cholesterol, urea and the like. More particularly, this invention relates to a disposable biosensor that is inexpensive to manufacture. Even more particularly, this invention relates to a disposable biosensor and method that accurately measures various analytes such as creatinine, creatine, glucose, cholesterol and the like in small volume biological fluid samples. Still even more particularly, this invention relates to a method of measuring the concentration of various analytes in small volume biological fluid samples using a redox mediator and at least an enzyme based on the electrochemical mechanism.
2. Description of the Prior Art
Biosensors have been used in the determination of concentrations of various analytes in fluids for more than three decades. Of particular interest is the measurement of blood glucose, creatinine, creatine, and cholesterol.
It is well known that the concentration of blood glucose is extremely important for maintaining homeostasis. Products that measure fluctuations in a person's blood sugar, or glucose levels, have become everyday necessities for many of the nation's millions of diabetics. Because this disorder can cause dangerous anomalies in blood chemistry and is believed to be a contributor to vision loss and kidney failure, most diabetics need to test themselves periodically and adjust their glucose level accordingly, usually with insulin injections. If the concentration of blood glucose is below the normal range, patients can suffer from unconsciousness and lowered blood pressure that may even result in death. If the blood glucose concentration is higher than the normal range, the excess blood glucose can result in synthesis of fatty acids and cholesterol, and in diabetics, coma. Thus, the measurement of blood glucose levels has become a daily necessity for diabetic individuals who control their level of blood glucose by insulin therapy.
Patients who are insulin dependent are instructed by doctors to check their blood-sugar levels as often as four times a day. To accommodate a normal life style to the need of frequent monitoring of glucose levels, home blood glucose testing was made available with the development of reagent strips for whole blood testing.
One type of blood glucose biosensors is an enzyme electrode combined with a mediator compound that shuttles electrons between the enzyme and the electrode resulting in a measurable current signal when glucose is present. The most commonly used mediators are potassium ferricyanide, ferrocene and its derivatives, as well as other metal-complexes. Many sensors based on this type of electrode have been disclosed. Examples of this type of device are disclosed in the following patents.
U.S. Pat. No. 5,628,890 (1997, Carter et al.) discloses an electrode strip having an electrode support, a reference or counter electrode disposed on the support, a working electrode spaced from the reference or counter electrode on the support, a covering layer defining an enclosed space over the reference and working electrodes and having an aperture for receiving a sample into the enclosed space, and a plurality of mesh layers interposed in the enclosed space between the covering layer and the support. The covering layer has a sample application aperture spaced from the electrodes. The working electrode includes an enzyme capable of catalyzing a reaction involving a substrate for the enzyme and a mediator capable of transferring electrons between the enzyme-catalyzed reaction and the working electrode.
U.S. Pat. No. 5,708,247 (1998, McAleer et al.) discloses a disposable glucose test strip having a substrate, a reference electrode, a working electrode, and a means for making an electrical connection. The working electrode has a conductive base layer and a coating layer disposed over the conductive base layer. The coating layer is a filler having both hydrophobic and hydrophilic surface regions that form a network, an enzyme and a mediator.
U.S. Pat. No. 5,682,884 (1997, Hill et al.) discloses a strip electrode with screen printing. The strip has an elongated support that includes a first and second conductor each extending along the support. An active electrode, positioned to contact the liquid mixture and the first conductor, has a deposit of an enzyme capable of catalyzing a reaction and an electron mediator. A reference electrode is positioned to contact the mixture and the second conductor.
U.S. Pat. No. 5,762,770 (1998, Pritchard et al.) discloses an electrochemical biosensor test strip that has a minimum volume blood sample requirement of about 9 microliters. The test strip has a working and counter electrodes that are substantially the same size and made of the same electrically conducting material placed on a first insulating substrate. Overlaying the electrodes is a second insulating substrate that includes a cutout portion that forms a reagent well. The cutout portion exposes a smaller area of the counter electrode than the working electrode. A reagent for analysis of an analyte substantially covers the exposed areas of the working and counter electrodes in the reagent well. Overlaying the reagent well and affixed to the second insulating substrate is a spreading mesh that is impregnated with a surfactant.
U.S. Pat. No. 5,755,953 (1998, Henning et al.) discloses a reduced-interference biosensor. The device generally comprises an electrode used to electrochemically measure the concentration of an analyte of interest in a solution. The device Includes a peroxidase enzyme covalently bound to microparticle carbon and retained in a matrix In intimate contact with the electrode. According to this disclosure, it is the enzyme/microparticle carbon of the device that provides a composition that displays little sensitivity to known interfering substances.
It is well known that creatinine is a waste product derived from creatine and excreted by the kidneys. The analytical determination of creatinine in urine, serum or plasma is a widely used and extremely Important test for renal dysfunction. Measurements of creatinine in serum or urine may also be used as indices in the diagnosis and treatment of other disorders such as muscular dystrophy and hypothyroidism. Thus, the creatinine assay has been a widely recognized as having vital medical significance. Further, dietary changes have little if any influence on the creatinine concentration in blood and urine. Although creatinine is primarily a waste product, and as such plays no important role in biochemical functions of the body, its chemical precursor, creatine, has a vital biochemical role. Creatine is a basic building block of creatine phosphate, which is the primary form of energy storage in muscle. As a result, the creatinine level is an important diagnostic index for renal, muscular and thyroid function.
Spectrophotometry has been conventionally employed for measuring creatinine. The presence and concentration of creatinine in the above-mentioned body fluids is most frequently determined by the Jaffe reaction. In this reaction, creatinine reacts with picric acid to produce a red color, a red tautomer of creatinine picrate. This method suffers from serious disadvantages including, but not limited to, the instability of alkaline picrate solutions and the concomitant necessity for preparing solutions as needed, interference from blood metabolites, the analytical time required to perform the method, and the lack of specificity.
Sensors have been developed for the detection of creatinine based on enzymatic cleavage of creatinine. Among them, electrochemical methods received particular attention. Rechnitz et. al. (T
Cai Xiaohua
Winarta Handani
Young Chung Chang
Deleault, Esq. Robert R.
Mesmer & Deleault, PLLC
Nova Biomedical Corporation
Olsen Kaj K.
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