Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2000-11-27
2003-07-29
Tung, T. (Department: 1753)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S403140, C204S403010, C204S416000, C204S291000, C204S292000, C204S293000, C204S294000
Reexamination Certificate
active
06599408
ABSTRACT:
FIELD OF INVENTION
This invention relates to a polymer thick film (PTF) composition containing a metal catalyst and graphite, which can be used to print sensing/working electrodes for electrochemical biosensors based on hydrogen peroxide detection. Electrochemical biosensors which are combinations of an electrochemical sensor and a biomolecule recognition element are useful in the analyses of biological analytes such as glucose, cholesterol, creatinine, alcohol, uric acid and lactate in body fluid, and are therefore useful in the field of medical devices and analytical instruments for medical diagnostics.
BACKGROUND OF THE INVENTION
The majority of amperometric electrochemical biosensors fall within two categories: (1) metal-catalyzed electrochemical biosensors or (2) electron-transfer mediator modified electrochemical biosensors. For example, a metal-catalyzed glucose sensor detects the hydrogen peroxide by-product which is produced in a one-to-one ratio from glucose through an enzyme-catalyzed air oxidation process, such as:
Glucose+O
2
glucose oxidase (GOD)
>glucolactone+H
2
O
2
U.S. Pat. No. 3,539,455 (1970) by Clark discloses a platinum based glucose sensor useful for self-monitoring of glucose by diabetics. Guilbault and Lubrano (1973) reported amperometric biosensors having an immobilized-enzyme platinum electrodes suitable for glucose sensor applications. Mizutani et al. (1992) reported a platinum/carbon paste (CP) composition with a 1/9 Pt/C ratio suitable for making glucose sensors. U.S. Pat. No. 4,970,145 (1990) to Bennetto et al. discloses a biosensor with a porous enzyme electrode comprising platinized carbon paper having a fluoropolymer binder. These platinum/C based biosensors have sensitivity for detection of glucose only at concentrations of millimolar (mM) glucose with an electric current response of <20 uA/cm
2
mM glucose. Furthermore, the use of a metal or metal/carbon with a high metal content as the working electrode leads to high material costs and has a drawback of loosing hydrogen peroxide due to the metal-catalyzed decomposition of hydrogen peroxide.
An electron-transfer mediator modified electrochemical biosensor relies on a fast electron-transfer mediator, which is typically an outer-sphere metal complex or organic compound, to assist the shuttling of electrons from reduced enzyme molecules to the working electrode. The reduced enzyme results from an enzyme molecule receiving two electrons from a glucose molecule, such as:
Glucose+(GOD)
oxidized
→Glucolactone+(GOD)
reduced
Electrochemical biosensors having carbon based working electrodes modified with electron-transfer mediators have been reviewed by Wring and Hart (1992). Biosensors having working electrodes modified with redox polymers have been reviewed by Pishko (1995). These mediator modified biosensors are capable of measuring glucose at mM concentration with an electric current response of <20 uA/cm
2
.mM glucose. There remains a need for materials suitable for fabrication of enzyme electrodes with high catalytic activity/current response and low background current noise to expand the capability of biosensors for monitoring biological analytes at the micro-molar (uM) level and to assure a high confidence of detecting low level of analystes in body fluids. One example was given by Tamada, Bohannon and Potts (1995) who reported the iontophoretic extraction of body fluid. The body fluid can then be analyzed in situ for a glucose levels and thus provide a method for non-invasive monitoring of glucose. The glucose concentration in the extracted body fluid is typically in the micro-molar level which produced electric current in the nano-ampere (nA) level, and thus requires a biosensor with low detection limit of glucose determination. A key limiting factor which affects the glucose detection limit is electrochemical signal noise or background current, which may be from electrochemically active impurities or temperature fluctuation etc. It is desirable that a biosensor has low background current which also does not greatly vary with temperature fluctuation.
Furthermore, it is desirable that catalyst materials for the working electrode be low cost and suitable for low cost fabrication of disposable biosensors by conventional printing processes. It is the object of the invention to overcome the deficiencies of current carbon-based materials for working electrodes.
SUMMARY OF INVENTION
The invention is directed to a polymer thick film conductor composition comprising, based on solids: (a) 0.1-5% wt. conductive metal particles selected from the group consisting of finely divided powders of platinum group metals and mixtures; (b) 62-85% wt. of graphite conductive filler; and (c) 14-35% wt. of a thermoplastic polymer.
The invention is still further directed to a conductor composition for use in electrochemical sensor applications comprising, based on solids: metallized particles comprising platinum group metal particles and mixtures thereof; deposited on support particles selected from graphite, surface modified graphite and mixtures thereof; with the provisos wherein the platinum group metal particles and mixtures thereof are in the range of 0.1-5% wt. and wherein the support particles and any optional graphite conductive filler are in the range of 62-85% wt.; and 14-35% wt. thermoplastic polymer.
DETAILED DESCRIPTION OF THE INVENTION
The PTF compositions covered in the present invention are intended for use in printing sensing or working electrodes in electrochemical biosensor applications, and more specifically, amperometric glucose sensors. The PTF composition offers glucose sensors with enzyme electrodes extremely high sensitivity for analysis of glucose at micro-molar levels, for example, a method for non-invasive monitoring of analytes transdermally extracted from the body.
The PTF conductive composition is designed to have the following characteristics when used as a working electrode:
(a) Printed PTF working electrodes have high electrocatalytic activity toward a target chemical or biomolecule, and therefore are able to provide strong electrical signal even at extremely low concentrations of the target chemical. Furthermore, the PTF working electrode should not introduce background current signal noise which would limit the ability of a biosensor to detect low concentrations of a target chemical.
(b) The PTF conductive composition is designed to have stable and consistent electrocatalytic activity enabling the biosensor to handle multiple analyses for continual glucose monitoring.
c) The PTF composition is intended for use in manufacturing of disposable biosensors and it is designed to be low cost.
d) The PTF composition has good rheological properties to facilitate manufacturing of sensors by conventional printing processes.
Through a unique combination of platinum group metal electrocatalysts and graphite materials, a low cost electrocatalyst system containing as low as 0.5/99.5 of metal/graphite ratio produces a biosensor working electrode to detect glucose levels of 100 nano-molar. This unique electrocatalyst in combination with a thermoplastic resin solution provides a low cost and reliable graphite-based PTF conductive composition for use in making disposable biosensors.
In this invention, the PTF conductive composition comprises the following components: (A) metal electrocatalyst selected from the platinum group which converts a chemical signal to an electrical signal (B) a conductive filler particles that provide electrical conductive pathways for the electrical signal, (C) a polymer that serves as the matrix resin holding (A) and (B) in a coating adhering to a plastic film substrate, and (D) an organic vehicle when mixed with the other ingredients make a composition for easy processing and printing of sensors.
A. Electrocatalyst
Electrocatalysts may be utilized in the present invention in two forms: (1) platinum group metal powders or (2) platinum group metals deposited on electrically conductive supports.
(1) Platinum Group Metal Powders
Precious meta
Chan Man-Sheung
Kuty Donald W.
E. I. du Pont de Nemours and Company
Noguerola Alex
Tung T.
LandOfFree
Thick film conductor composition for use in biosensors does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Thick film conductor composition for use in biosensors, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Thick film conductor composition for use in biosensors will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3071311