U.S. patent application number 10/993317 was filed with the patent office on 2005-03-31 for method of making sensor.
Invention is credited to Hajizadeh, Kiamars, Mills, Kelly, Rappin, Craig.
Application Number | 20050067737 10/993317 |
Document ID | / |
Family ID | 26690266 |
Filed Date | 2005-03-31 |
United States Patent
Application |
20050067737 |
Kind Code |
A1 |
Rappin, Craig ; et
al. |
March 31, 2005 |
Method of making sensor
Abstract
A sensor is provided for the determination of various
concentrations of one or more components within a fluid sample. The
sensor includes an injection molded body, at least two electrodes,
an enzyme, and if desired, an electron transfer mediator. The body
includes a reaction zone for receiving a fluid sample. The
electrodes are at least partially embedded within the plastic body
and extend into the reaction zone. Also contained within the
reaction zone is an enzyme capable of catalyzing a reaction
involving a compound within the fluid sample. Additionally, the
sensor incorporates fill detection which activates a meter,
attached to the sensor, for measuring the electrochemical changes
occurring in the reaction zone.
Inventors: |
Rappin, Craig; (Long Grove,
IL) ; Hajizadeh, Kiamars; (Lincolnshire, IL) ;
Mills, Kelly; (McHenry, IL) |
Correspondence
Address: |
ROGER H. STEIN, ESQ.
WALLENSTEIN & WAGNER, LTD.
53RD FLOOR
311 SOUTH WACKER DRIVE
CHICAGO
IL
60606
US
|
Family ID: |
26690266 |
Appl. No.: |
10/993317 |
Filed: |
November 19, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10993317 |
Nov 19, 2004 |
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10419581 |
Apr 21, 2003 |
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6849216 |
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10419581 |
Apr 21, 2003 |
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10017751 |
Dec 7, 2001 |
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6572745 |
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10017751 |
Dec 7, 2001 |
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09820372 |
Mar 23, 2001 |
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6576102 |
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Current U.S.
Class: |
264/272.19 ;
204/424 |
Current CPC
Class: |
Y10T 29/49002 20150115;
G01N 27/3272 20130101 |
Class at
Publication: |
264/272.19 ;
204/424 |
International
Class: |
B29C 031/00; G01N
027/26 |
Claims
We claim:
1. A method of making a testing device for testing a fluid sample
comprising the steps of: positioning and holding in place at least
two spaced apart electrically conductive electrodes in a mold;
molding a body within the mold of insulative material to at least
either embed or encase a part of the electrodes in the insulative
material and to permit exposure of at least a portion of one
electrode to a fluid sample reaction zone by forming a channel with
the mold; and, treating at least one of the electrodes with one or
more substances either before or after the molding of the body for
reacting with the fluid sample to be tested.
2. The method of claim 1 wherein the electrically conductive
electrodes are substantially molded into the insulative material
with at least a part thereof either embedded within or encased by
the insulative material and the electrodes are disposed in fixed
longitudinal relation in the insulative material.
3. The method of claim 1 wherein the molding step includes forming
a hinge in the body for permitting the pivoting and connecting of a
portion of the body onto itself.
4. The method of claim 1 wherein the molding step comprises molding
the body in two pieces, an electrode-encasing housing and an end
cap, both of the pieces being hingeably attachable to one another
after the molding is completed.
5. The method of claim 1 wherein the molding step includes molding
into the body a means for receiving the fluid sample.
6. The method of claim 8 wherein the means for receiving the fluid
sample includes a capillary inlet in the body in communication with
a reaction zone and a vent.
7. The method of claim 1 wherein the molding step includes forming
a vent in the body for detecting when the sensor contains a
sufficient quantity of fluid sample for testing.
8. The method of claim 1 wherein the molding step includes molding
into the body a means for detecting the presence of an adequate
amount of sample.
9. A method of making an electrochemical device for cooperating
with a meter to measure electrical properties between at least two
electrically conductive electrodes, comprising the steps of:
positioning and holding in place at least two spaced apart
electrically conductive electrodes in a mold; molding a body within
the mold of insulative material to at least either embed or encase
a portion of the electrodes in the insulative material and to
permit exposure of at least a portion of one electrode to a fluid
sample to be tested; and, depositing one or more substances on at
least one of the electrodes either before or after the molding of
the body to react with the fluid sample to be tested and to change
the electrical properties between the electrodes.
10. The method of claim 9 wherein the electrically conductive
electrodes are substantially molded into the insulative material
with at least a part thereof either embedded within or encased by
the insulative material and the electrodes are disposed in fixed
longitudinal relation in the insulative material.
11. A method of making a testing device for testing a fluid sample
comprising the steps of: positioning and holding in place at least
two spaced apart electrically conductive electrodes in a mold; and,
molding a body within the mold of insulative material to at least
either embed or encase a part of the electrodes in the insulative
material and to permit exposure of at least a portion of one
electrode to a fluid sample reaction zone by forming a channel with
the mold, the molding step forming a hinge in the body for
permitting the pivoting and connecting of a portion of the body
onto itself.
12. The method of claim 11 wherein the electrodes are held in place
during the molding step by fingers passing through apertures formed
in the body.
13. The method of claim 11 further comprising severing a connecting
segment via an aperture formed in the body, the connecting segment
electrically connecting the at least two spaced apart electrically
conductive electrodes prior to severing the connecting segment.
14. A method of making a testing device for testing a fluid sample,
comprising the steps of: positioning a first electrode and a second
electrode in a mold; molding a body of insulative material within
the mold to either embed or encase a first portion of the first
electrode and a first portion of the second electrode in the
insulative material and to permit exposure of a second portion of
the first electrode and a second portion of the second electrode;
and, holding the first electrode and the second electrode in place
during the molding step using one or more projections passing
through the body.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of copending prior U.S.
application Ser. No. 10/419,581 filed Apr. 21, 2003, which is a
Divisional of U.S. application Ser. No. 10/017,751 filed Dec. 7,
2001, (now U.S. Pat. No. 6,572,745 issued Jun. 3, 2003) which is a
Continuation-In-Part of U.S. application Ser. No. 09/820,372, filed
Mar. 23, 2001 (now U.S. Pat. No. 6,576,102 issued Jun. 10,
2003).
TECHNICAL FIELD
[0002] The present invention generally relates to electrochemical
sensors and, in particular, to molded electrochemical sensors for
detection or measurement of analytes in test samples, such as
fluids and dissolved solid materials, and the methods of making and
using these sensors.
BACKGROUND OF THE INVENTION
[0003] Electrochemical sensors are used to determine the
concentrations of various analytes in testing samples such as
fluids and dissolved solid materials. For instance, electrochemical
sensors have been made for measuring glucose in human blood. Such
sensors have been used by diabetics and health care professionals
for monitoring blood glucose levels. The sensors are usually used
in conjunction with a meter, which measures light reflectance, if
the strip is designed for photometric detection of a die, or which
measures some electrical property, such as electrical current, if
the strip is designed for detection of an electroactive
compound.
[0004] Typically, electrochemical sensors are manufactured using an
electrically insulating base upon which conductive inks such as
carbon and silver are printed by screen printing to form conductive
electrode tracks or thin strips of metal are unrolled to form the
conductive electrode tracks. The electrodes are the sensing
elements of the sensor generally referred to as a transducer. The
electrodes are covered with a reagent layer comprising a
hydrophilic polymer in combination with an oxidoreductase or a
dehydrogenase enzyme specific for the analyte. Further, mounted
over a portion of the base and the electrodes is an insulating
layer.
[0005] Precision and accuracy of electrochemical measurements to a
great extent rely on the reproducibility of the electrode surface
area on a microscopic scale. Variations in the morphology of the
electrode can result in very significant changes in the
electrochemical signal readout. Screen-printing has made
significant in-roads in the production of sensors for determining
glucose. The wide use of screen-printing stems from the ability to
mass-produce relatively inexpensive sensors. The use of metal
strips unrolled from large rolls has also been employed to mass
produce such sensors.
[0006] While many advances have been made in the field of screen
printing and conductive ink production, the technology still
suffers from poor reproducibility of the electrode surface area,
dimensional variations, thickness variations, micro-cracks, and
shrinkage due to the repetitive and high temperature curing
processes involved in using film printing technology. Loss of
solvent during printing is another factor that leads to variations
in the thickness of electrodes.
[0007] Sensor development using printing technology requires
several passes of different conductive inks demanding different
screens. Slight variations in positioning the screens can lead to
substantial errors in IR drop and the applied potentials. Wear and
tear of these screens is another source of error. Also, sensor
strip production by screen printing suffers from a high level of
raw material waste. Generally, for every gram of ink used, there is
a gram of ink wasted. Manufacture of such sensors also involves
several lamination processes that add to the production complexity
and cost of the final product.
SUMMARY OF THE INVENTION
[0008] The present invention is an electrochemical sensor that
provides for the determination of various analyte concentrations in
a testing sample such as fluids and dissolved solid materials. The
sensor is designed to facilitate production in large quantities
using reliable and cost effective injection molding manufacturing
methods. The present invention includes an injection molded plastic
strip or body, at least two electrodes, an enzyme, and if desired,
an electron transfer mediator. The body includes a cavity or
reaction zone for receiving a fluid sample. The electrodes are at
least partially embedded within the plastic body and extend into
the reaction zone where they are exposed to a test sample. Also
contained within the reaction zone is an enzyme capable of
catalyzing a reaction involving a compound within the fluid
sample.
[0009] Specifically, the device cooperates with an electronic meter
capable of measuring the difference between the electrical
properties of the electrically conductive electrodes within the
device. The device, a sensor, includes at least two, and preferably
three, spaced apart electrically conductive electrodes, a body
having two ends of insulative material molded about and housing the
electrodes, means for connecting the meter to the housing, means
for receiving a fluid sample, and means for treating one or more
electrodes with one or more chemicals to change the electrical
properties of the treated electrodes upon contact with the fluid
sample. One end of the housing has the means for connecting the
meter and the opposite end of the housing has the means for
receiving the fluid sample. The means for connecting the meter is a
plug formed in the housing exposing the electrodes outside the
body.
[0010] The sensor is molded and can be a single, unitary piece or
two pieces. In the two piece construction, an end cap is attached
to the body. In the single piece construction, the body pivots
about a hinge and connects onto itself. Protuberances formed in a
portion of the body cooperate with troughs to ensure proper
alignment.
[0011] A capillary inlet is constructed at one end of the sensor to
draw the fluid sample into the body upon contact with the fluid
sample. The capillary inlet is molded into the end of the body and
is in communications with a reaction zone. This reaction zone is a
channel formed in the body about the electrodes and is adapted for
reacting with the fluid drawn into the body by the capillary force.
While the reaction zone may be formed above or below the
electrodes, the preference has been to construct it above the
electrodes. The capillary has a vent for relieving pressure.
[0012] As noted, the electrodes are molded into the plastic. In one
embodiment, the electrodes are conductive wires. In another
embodiment, the electrodes are constructed from a metal plate. The
electrodes may be coated with a different conductive material to
enhance their performance.
[0013] Apertures are formed in the body of the sensor to permit the
holding of the electrodes during the molding process. Apertures may
also be formed in the body to chemically treat one or more
electrodes in the reaction zone before or after the molding
process. Adding chemicals (e.g., reagents with and without enzymes)
changes the electrical properties of the treated electrodes upon
contact with the fluid sample. In the preferred embodiment, the
enzyme is applied to the outer surface of one of the electrodes. An
antibody may also be applied to another of the electrodes. An
electron mediator may further be applied to the outer surface of
one or more of the electrodes.
[0014] In another embodiment in accordance with the invention, the
sensor provides fill detection. Fluid drawn into the capillary
inlet and the reaction zone contacts the edges of the electrodes,
and upon reaching the lower end of the reaction zone, the area
farthest from the capillary inlet, activates the meter. When the
fluid comes in contact with the last electrode in the capillary
space, it closes an open circuit in the electrochemical cell
causing current to flow through the cell. The flow of current in
the cell triggers the meter, signaling that the capillary chamber
is filled with fluid. The vent could also be used for a visual
detection of fluid fill.
[0015] The methods of making and using the electrochemical sensor
are also disclosed. The method of making the device includes the
steps of positioning at least two spaced apart electrically
conductive electrodes in a mold, before or after molding treating
at least one of the electrodes with one or more chemicals to change
the electrical properties of the treated electrode upon contact
with a fluid sample, and molding a body of insulative material with
two ends around the electrodes with one end having therein means
for receiving a fluid sample. As before, the body is molded in two
pieces, with a body and end cap for attaching to one another after
the molding is completed, or in a single, unitary piece.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] In the accompanying drawings forming part of the
specification, and in which like numerals are employed to designate
like parts throughout the same,
[0017] FIG. 1 is an enlarged top plan view of a first embodiment of
an electrochemical sensor made in accordance with the teachings of
the present invention;
[0018] FIG. 2 is a sectional end view of the electrochemical sensor
of FIG. 1 taken along plane 2-2;
[0019] FIG. 3 is a sectional end view of the electrochemical sensor
of FIG. 1 taken along plane 3-3;
[0020] FIG. 4 is a sectional end view of the electrochemical sensor
of FIG. 1 taken along plane 4-4;
[0021] FIG. 5 is a sectional end view of the electrochemical sensor
of FIG. 1 taken along plane 5-5;
[0022] FIG. 6 is a sectional side view of the electrochemical
sensor of FIG. 1 taken along plane 6-6;
[0023] FIG. 7 is an enlarged top plan view of a second embodiment
of an electrochemical sensor made in accordance with the teachings
of the present invention;
[0024] FIG. 8 is an end elevation view of the electrochemical
sensor of FIG. 7;
[0025] FIG. 9 is a side elevation view of the electrochemical
sensor of FIG. 7;
[0026] FIG. 10 is a bottom plan view of the electrochemical sensor
of FIG. 7;
[0027] FIG. 11 is a sectional end view of the electrochemical
sensor of FIG. 7 taken along plane 11-11;
[0028] FIG. 12 is a sectional end view of the electrochemical
sensor of FIG. 7 taken along plane 12-12;
[0029] FIG. 13 shows an enlarged top plan view of a third
embodiment of an electrochemical sensor made in accordance with the
teachings of the present invention;
[0030] FIG. 14 shows an enlarged bottom plan view of the
electrochemical sensor of FIG. 13;
[0031] FIG. 15 is a sectional side view of the electrochemical
sensor of FIG. 13 taken along plane 15-15;
[0032] FIG. 16 is a sectional end view of the electrochemical
sensor of FIG. 13 taken along plane 16-16;
[0033] FIG. 17 shows a top plan view of a third embodiment of an
electrochemical sensor made in accordance with the teachings of the
present invention;
[0034] FIG. 18 shows an enlarged bottom view of the electrochemical
sensor of FIG. 17;
[0035] FIG. 19 shows a sectional side view of the electrochemical
sensor of FIG. 17 taken along plan 19-19; and,
[0036] FIGS. 20a,b show a magnified view of the terminal end
portion of the sensor of FIG. 17 having the end cap (a) extended
away from the body and (b) secured to the body.
DETAILED DESCRIPTION
[0037] While this invention is susceptible of embodiments in many
different forms, there is shown in the drawings and will herein be
described in detail preferred embodiments of the invention with the
understanding the present disclosure is to be considered as an
exemplification of the principles of the invention and is not
intended to limit the broad aspect of the invention to the
embodiments illustrated.
[0038] The First Embodiment
[0039] Referring to FIGS. 1-6, an electrochemical sensor in
accordance with the present invention, first embodiment, is
depicted. FIG. 1 shows the sensor 10 as though it were made out of
clear plastic, permitting one to look inside it. As discussed
herein, the internal components and hidden external components
would not normally be visible looking down on the sensor 10. This
rendition would be similar to a view taken along plane x-x in FIG.
2.
[0040] The sensor or test strip of the first embodiment 10 includes
an injection molded plastic body 12, opaque or preferably
translucent, having a meter attachment end or plug end 14 and a
fluid sample receiving end 16. The body has a bottom surface 13, a
top surface 15 and a tapered portion 20 connecting a first top
surface 15a to a second top surface 15b, the first top surface
being lower than the second top surface, and a third top surface
15c, also lower than the second top surface. The body 12 contains
three spaced apart electrodes 30,31,32. The plug end 14 of the body
12 includes a pair of tapered side edges 18,19 and a wedge shaped
top portion 20. The tapered side edges 18,19 facilitate a user
inserting the sensor's plug end 14 into the socket cavity of a
conventional meter (not shown). Moreover, the wedged portion 20 of
the sensor serves as a stop, and frictionally holds the sensor 10
within the socket cavity of the meter.
[0041] The fluid sample receiving end 16 of the sensor 10 includes
an electrochemical reaction zone 24 adjacent the terminal end 16 of
the body. This reaction zone 24 is a channel formed in the third
top surface 15c and about/adjacent the electrodes 30,31,32 in the
body 12 for analyzing the fluid drawn into the body 12 for a
particular analyte. While the reaction zone may be formed above or
below the electrodes, the preference has been to construct it above
the electrodes. An end cap 27 is welded [by ultrasonics or
adhesive] over the reaction zone 24 and onto the third top surface
15c. The top of the end cap 27 aligns with the top 15,15b of the
body 12. The end cap 27 is preferably made of the same material as
the molded body 12 and attached thereto by ultrasonic welding or
gluing.
[0042] While the cap 27 is shown as a separate piece, it can also
be constructed as part of the body 12 and hingeably connected to
the body such that it can be pivoted onto the third top surface 15c
and attached [e.g., see The Second Embodiment]. In this manner, the
entire sensor can be made at one time and as one molded, unitary
piece.
[0043] A capillary opening 28 is formed in the terminal end 16 of
the sensor 10 when the cap 27 is welded (or folded) to the body 12.
This capillary opening leads to the reaction zone 24. Preferably,
the sensor 10 is a capillary fill device, that is, the reaction
zone 24 is small enough to draw a fluid sample into the zone when
the capillary opening or inlet 28 is placed in contact with the
fluid being tested, such as a drop of blood. Accordingly, if one
wants to test his/her blood, s/he touches the terminal end 16 to
the blood and the blood is drawn into the sensor 10 and reaction
zone 24 through the capillary opening 28. This is much easier than
placing the sample (such as blood) on the sensor and on a target
zone as in the prior art. To effectuate the capillary effect with
the capillary opening 28 to the reaction zone 24, a vent 29 is
constructed into the cap 27. This vent is in communication with the
reaction zone 24. This vent 29 releases air pressure as the
reaction zone 24 draws and fills with fluid. For additional
discussion regarding capillary filling, see U.S. Pat. Nos.
4,254,083; 4,413,407; 4,473,457; 5,798,031; 5,120,420; and
5,575,895, the disclosures of which are hereby incorporated by
reference.
[0044] Mostly encased within the injection molded body 12 are a
plurality of electrically conductive leads or electrodes 30,31,32.
Preferably, the body 12 is molded about these leads 30,31,32. As
noted, these leads are spaced from one another. They 30,31,32 are
primarily encased in the body 12 and run from the plug end 14 to
the reaction zone 24, just before the terminal end 16. The leads'
30,31,32 ends 26 are positioned just before the terminal end 16 of
the sensor.
[0045] The conductive leads 30,31,32 consist of an electrically
conductive material like metal or metal alloy such as platinum,
palladium, gold, silver, nickel, nickel-chrome, stainless steel,
copper or the like. Moreover, each lead preferably consists of a
single wire, or in an alternative preferred embodiment (See The
Second Embodiment), a stamped metal member plated with gold or the
like. In the first embodiment, the outer leads 30 and 32 are
equally spaced from the inner lead 31 with the spacing of the leads
at the fluid sample receiving end 16 of the body 12 being closer
together than at the meter attachment end 14.
[0046] Segments 33 of the leads 30,31,32 are exposed about the plug
end 14 of the body 12 to provide contact surface areas 34,35,36
respectively with the meter (not shown). Preferably, the exposed
contact surface areas 34,35,36 extend from the tapered top portion
20 of the body 12 to the plug end 14 of the body 12 on or partially
embedded into the first top surface 15a. Specifically, the body 12
may be molded such that the segments 33 of the leads 31,31,32 are
embedded (partially molded into the first top surface 15a) and held
by the body 12 opposite the contact surface areas 34,35,36. In this
manner, the leads are exposed for contact with the meter and
maintained in a position without the use of adhesives or
welding.
[0047] The portion of the leads 30,31,32 between the sensor plug
end 14 and the fluid sample receiving end 16 are embedded within
the plastic injection molded body 12. Accordingly, the body 12 is
constructed of an electrically insulating injection moldable
plastic.
[0048] Certain structural support components are molded within the
body 12 of the sensor 10 to hold and maintain the leads 30,31,32
within the body, in spaced relationship to one another, during and
after the molding process. Specifically, guide blocks 42 and
alignment pins 44 are molded within the body 12 for proper mounting
of the leads 30,31,32. Apertures are also formed in the top surface
15 and bottom surface 13 of the body 12 for permitting the ingress
and egress of fingers into the mold during the molding process (to
be discussed below). In particular, a first aperture 46 is molded
into the second top surface 15b and a second aperture 48 and third
aperture 50 are formed into the bottom surface 13 of the body 12.
Once the molding is completed, each of these apertures 46,48,50 is
covered up or sealed with plastic (e.g., the same plastic used in
the molding process) or left open. Their 46,48,50 sizes are
relatively small; leaving them open should not cause any safety
issues or affect the sensor's ability. Fingers cannot fit into the
apertures and debris from the outside will likely be unable to
enter the apertures and contact the leads 30,31,32.
[0049] Within the reaction zone 24, one lead 30 serves as a primary
working electrode 52, a second lead 31 acts as a reference or
counter electrode 53, and the third lead 32 serves as an auxiliary,
secondary or second working electrode 54. Desirably, the conductive
leads 30,31,32 (or electrodes 52,53,54) are the only leads
(electrodes) coming into contact with the test sample of fluid
entering the sensor 10. The electrodes 52,53,54 are electrically
insulated from the rest of the sensor 10 by molded plastic to
ensure a signal carried by the leads arises only from that portion
exposed to the test sample in the electrochemical reaction zone
24.
[0050] In the embodiment, an enzyme 56 is applied to the outer
surface of the primary working electrode 52 and, if desired, an
electron transfer mediator. The enzyme can consist of, for
instance, flavo-proteins, pqq-enzymes, haem-containing enzymes,
oxidoreductase, or the like. For additional discussion regarding
mediators, see U.S. Pat. Nos. 4,545,382 and 4,224,125, the
disclosures of which are hereby incorporated by reference. In an
alternative embodiment, an antibody 57 can be applied to the outer
surface of the secondary working electrode 54. As such, the
reaction zone 24 can contain antibodies, enzyme-antibody
conjugates, enzyme-analyte conjugates, and the like. It should be
noted that an enzyme 56 can also be applied to the second working
electrode 54 and an antibody can be applied to the outer surface of
the primary working electrode 52.
[0051] As will be appreciated by those having skill in the art, the
enzyme 56 is specific for the test to be performed by the sensor
10. For instance, the working electrode 52, or secondary working
electrode 54, or both, can be coated with an enzyme 56 such as
glucose oxidase or glucose dehydrogenase formulated to react at
different levels or intensities for the measurement of glucose in a
human blood sample. Thus, as an individual's body glucose
concentration increases, the enzyme 56 will make more products. The
glucose sensor is used with a meter to measure the electrochemical
signal, such as electrical current, arising from oxidation or
reduction of the enzymatic turnover product(s). The magnitude of
the signal is directly proportional to the glucose concentration or
any other compound for which a specific enzyme has been coated on
the electrodes.
[0052] In an embodiment, the enzyme 56 can be applied to the entire
exposed surface area of the primary electrode 52 (or secondary
electrode 54). Alternatively, the entire exposed area of the
electrode may not need to be covered with the enzyme as long as a
well defined area of the electrode is covered with the enzyme.
[0053] In a further embodiment and as shown in the prior art, an
enzyme 57 can be applied to all the electrodes 52,53,54 in the
reaction zone 24 and measures can be taken by a meter.
[0054] In the preferred embodiment, one of the working electrodes
(52 or 54) is selectively coated with the enzyme 57 carrying a
reagent with the enzyme and the other working electrode (54 or 52)
is coated with a reagent lacking the respective enzyme. As such,
with a meter, one can simultaneously acquire an electrochemical
signal from each working electrode and correct for any "background
noise" arising from a sample matrix. Thus, the potential or current
between the reference and the electrode without the enzyme can be
compared with the potential or current between the reference and
the electrode with the enzyme. The measuring and comparing of the
potential and current differences are well known to those skilled
in the art.
[0055] As indicated above, the sensor 10 is used in conjunction
with a meter capable of measuring an electrical property of the
fluid sample after the addition of the fluid sample into the
reaction zone 24. The electrical property being measured may be,
for example, electrical current, electrical potential, electrical
charge, or impedance. An example of measuring changes in electrical
potential to perform an analytical test is illustrated by U.S. Pat.
No. 5,413,690, the disclosure of which is hereby incorporated by
reference.
[0056] An example of measuring electrical current to perform an
analytical test is illustrated by U.S. Pat. Nos. 5,288,636 and
5,508,171, the disclosures of which are hereby incorporated by
reference.
[0057] The plug end 14 of the sensor 10 can be inserted and
connected to a meter, which includes a power source (a battery).
Improvements in such meters and a sensor system are found in U.S.
Pat. Nos. 4,999,632; 5,243,516; 5,366,609; 5,352,351; 5,405,511;
and 5,438,271, the disclosures of which are hereby incorporated by
reference.
[0058] Many analyte-containing fluids can be analyzed by the
electrochemical sensor of the present invention. For example,
analytes in human and animal body fluids, such as whole blood,
blood serum and plasma, urine and cerebrospinal fluid may all be
measured. Also, analytes found in fermentation products, food and
agricultural products, and in environmental substances, which
potentially contain environmental contaminants, may be
measured.
[0059] The Molding Process of the First Embodiment
[0060] In the past, while recognized for its strength and
durability, plastic injection molding of sensors has been difficult
and thus avoided. One reason is the reluctance to mold around the
conductive wires or plates. The industry choice has been to make
such sensors like sandwiches, having a top and bottom piece with
the insides (conductive elements) being formed on one of the pieces
or placed between the pieces. The sandwich-like sensor is then
assembled together and sealed closed, such as with an adhesive.
[0061] The present invention molds the sensors with the conductive
elements inside the mold during the molding process. The advantages
are many. In addition to making a stronger more durable sensor,
such a process reduces labor involvement and steps and produces a
more consistent product.
[0062] While multiple sensors 10 can be produced with one mold, the
making of a single sensor will be discussed. The mold has the shape
of the body 12. The conductive wires 30,31,32 for the electrodes
are first molded into the product. Specifically, the wire leads are
fed into the mold and placed on or between figures [not shown]
projecting into the mold through the openings in the mold
(corresponding to the apertures 46,48,50) to hold the wires in
place and level during the set-up and molding process. In
particular, the bottom apertures permit the fingers projecting into
the mold to support the wires and the top apertures permit the
fingers projecting into the mold to hold the wires. The liquid
plastic is injected into the mold where it fills the mold. The
plastic is then cooled.
[0063] Once the plastic has formed and hardened, the fingers are
pulled from and exit the mold through the openings (apertures
46,48,50). The molded sensor 12 is next ejected from the mold.
[0064] The reagents are next applied to the electrodes after the
molding process is finished. First, after molding is finished, the
cap is treated with a surfactant that facilitates pulling or
drawing the fluid (e.g., test blood) into the capillary gap at the
end of the sensor. Then, the reagents (including the enzyme) are
applied to the electrodes.
[0065] The end cap 27 is thereafter connected to the main body 12
and any undesirable openings in the sensor can be sealed closed by
the same plastic used for the mold. In the alternative, the
chemicals can be applied to the wires after the end cap is married
to the body. Any extraneous wire(s) projecting from the sensor can
be cut and removed. Then, any desired writings on the sensor (e.g.,
manufacturing codes, product name, etc.) can then be applied to the
sensor by conventional means.
[0066] The Second Embodiment
[0067] Referring to FIGS. 7-12, an electrochemical sensor in
accordance with the present invention, second embodiment, is
depicted. In these figures, components similar to those in the
first embodiment (10) will be identified with the same reference
numbers, but in the 100 series. Specifically, FIG. 7 shows the
sensor 110 as though it were made out of clear plastic, permitting
one to look inside it. As noted previously, the internal components
and hidden external components would not normally be visible
looking down on the sensor 110. The sensor of the second embodiment
110 includes a molded plastic body 112 having a meter attachment
end or plug end 114 and a fluid sample receiving end 116. The body
has a bottom surface 113 and a top surface 115. An end cap 127 is
integral to the body 112 and molded with the body. A hinge 227
permits the pivoting of the end cap onto the main body as will be
explained. Specifically, the top surface 115 of the sensor 110 has
three top surfaces 115a,115b,115c. The first top surface 115a runs
most of the length of the body and terminates at a ledge 215; the
second top surface 115b is positioned below or is lower than the
first 115a; and, the third top surface 115c is separated from the
other two top surfaces 115a, 115b by the hinge 227. During
construction of the sensor 110, the end cap 127 is rotated about
the hinge such that the third top surface 115c abuts the second top
surface 115b, face-to-face, and rests adjacent the ledge 215 of the
top surface 115a. The bottom surface 13a of the cap 127 thus
becomes the top surface adjacent the first top surface 115a. See
FIG. 8. A pair of tapered protuberances 125 formed in the end cap
127 and a pair of tapered troughs 122 formed in the main body 112
align and mate when the cap is folded into place. This facilitates
and ensures correct alignment of the hinged parts.
[0068] The body 112 contains three spaced apart electrodes
130,131,132. The plug end 114 of the body 112 includes a pair of
tapered side edges 118,119 to facilitate a user inserting the
sensor's plug end 114 into the socket cavity of a conventional
meter (not shown).
[0069] The fluid sample receiving end 116 of the sensor 110
includes an electrochemical reaction zone 124 adjacent the terminal
end 116 of the body. This reaction zone 124 is a channel formed in
the second top surface 115b and about/adjacent the electrodes
130,131,132 in the body 112 for reacting with the fluid drawn into
the body 112. While this reaction zone may be formed above or below
the electrodes, the preference has been to construct it above the
electrodes. A ridge 327 is formed on the top surface (third top
surface 115c) of the end cap. This ridge prevents any fluid from
leaving the reaction zone 124 or debris from entering the reaction
zone once the end cap 127 is welded [by ultrasonics or adhesive]
onto the second top surface 115b. When the end cap is folded, it is
welded into position along the side surfaces of the piece 110.
Thus, the ridge can be collapsed during welding and not affect the
performance of the sensor. An optional channel 327a may be
constructed in the third top surface 115c to increase the height of
the reaction zone 124.
[0070] A capillary opening 128 is formed in the terminal end 116 of
the sensor 110 when the cap 127 is folded and welded into place.
This capillary opening leads to the reaction zone 124. The width of
the opening 128 is approximately the same as the length of the
sensing electrodes 130,131,132 exposed to the test fluid in the
reaction zone 124. The sensor 110 of the second embodiment is also
a capillary fill device, that is, the reaction zone 124 is small
enough to draw a fluid sample into the zone when the capillary
opening 128 is placed in contact with the fluid being tested. A
vent 129 provided in the cap 127 is in communication with the
reaction zone 124 to release pressure as the reaction zone 124
draws and fills with fluid. Preferably, the bottom or base of the
capillary inlet is flush with the top surface of electrodes
130,131,132.
[0071] Mostly encased within the injection molded body 112 is an
electrically conductive plate (stamped or cast) having leads or
electrodes 130,131,132. The body 112 is molded around the plate and
these leads 130,131,132. The conductive plate is a single piece of
material; it includes the leads 130,131,132 and connecting segments
230 and 231. When the sensor is made, the segments are connecting
the leads. After molding, the segments 230,231 are cut and/or
removed so that the leads are distinct and separated from one
another. If they were connected, the system would short
circuit.
[0072] The electrodes 130,131,132 are primarily encased in the body
112 and run from the plug end 114 into the reaction zone 124, just
before the terminal end 116. The leads 130,131,132 may be widened
if desired in the reaction zone to expose more surface area to the
fluid and chemicals contacting one another in the zone. The leads
130,131,132 can be as wide as the sensing parts. These leads
130,131,132 are an electrically conductive material like metal or
metal alloy such as platinum, palladium, gold, silver, nickel,
nickel-chrome, stainless steel, copper or the like. To enhance
their performance and sensitivity, they may also be coated, e.g.,
made of copper and coated with gold. In the second embodiment, the
leads 130,131,132 are spaced from and parallel to one another.
[0073] Segments 133 of the leads 130,131,132 extend outwardly from
the body 112 from the plug end 114 of the sensor 110 and are
exposed to provide contact surface areas 134,135,136 respectively
with the meter (not shown). These leads can also be embedded in the
molded plastic such that their upper surfaces are exposed in
portions.
[0074] As before, the portion of the leads 130,131,132 between the
sensor plug end 114 and the fluid sample receiving end 116 are
embedded, or encased, within the plastic injection molded body 112;
the body 112 is constructed of an electrically insulating injection
moldable plastic.
[0075] Apertures are formed in the top surface 15 and bottom
surface 113 of the body 112 for permitting the ingress and egress
of fingers into the mold during the molding process. In particular,
a set (3) of first apertures 146 and a set (3) of second apertures
147 are molded into the top surface 115a; a third aperture 148 and
fourth aperture 150 and a set (3) of fifth apertures 160,161,162
are formed into the bottom surface 113 of the body 112. Once the
molding is completed, each of these apertures 146,147,148,150 can
be covered up with plastic (e.g., the same plastic used in the
molding process) or left open.
[0076] Within the reaction zone 124, one outer lead 130 serves as a
primary working electrode 152, the center lead 131 acts as a
reference or counter electrode 153, and the other outer lead 132
serves as an auxiliary or secondary or second working electrode
154. These conductive leads 130,131,132 (or electrodes 152,153,154)
are the only leads (electrodes) coming into contact with the test
sample of fluid entering the sensor 110. The electrodes 152,153,154
are electrically insulated from the rest of the sensor 110 by
molded plastic to ensure a signal carried by the leads arises only
from that portion exposed to the test sample in the electrochemical
reaction zone 124.
[0077] As with the first embodiment, an enzyme 156 is applied to
the outer surface of the primary working electrode 152 and, if
desired, an electron transfer mediator. An antibody 157 may also be
applied to the outer surface of the secondary working electrode
154. An enzyme 156 can also be applied the second working electrode
154 and an antibody to the outer surface of the primary working
electrode 52.
[0078] The enzyme 156 can be applied to the entire exposed surface
area of the primary electrode 152 (or secondary electrode 154).
Alternatively, the entire exposed area of the electrode may not
need to be covered with the enzyme as long as a well defined area
of the electrode is covered with the enzyme. Or, an enzyme can be
applied to all the electrodes 152,153,154 in the reaction zone 124
and measurements can be taken by a meter. Preferably, one of the
working electrodes (152 or 154) is selectively coated with the
enzyme carrying a reagent with the enzyme and the other working
electrode (154 or 152) is coated with a reagent lacking the
respective enzyme.
[0079] The sensor 110 is used in conjunction with a meter capable
of measuring an electrical property of the fluid sample after the
addition of the fluid sample into the reaction zone 124. The plug
end 114 of the sensor 110 is inserted and connected to a meter, as
before with the first embodiment.
[0080] The Molding Process of the Second Embodiment
[0081] The mold has the shape of the body 112. The conductive
130,131,132 leads/electrodes (in the form of a plate with the
joining extensions 230,231 for the electrodes) are first treated
with any coatings (metal). The chemicals/reagents (with and without
enzymes) may also be applied before molding; or, they can be
applied after the molding. The plate is fed into the mold and
placed on or between fingers (not shown) projecting into the mold
through the openings in the mold (corresponding to the apertures
146,147,148,150) to hold the plate in place and level during the
set-up and molding process. Knives or punches (not shown) are also
inserted through the top surface of the mold (outline of opening
formed by the knives/punches 170). These knives punch and sever the
jointing extensions 230,231 and hold the bent portions in place
during molding (see FIG. 11). As before, the bottom apertures
permit the fingers projecting into the mold to support the plate
with leads and the top apertures permit the fingers projecting into
the mold to hold the plate and leads. The liquid plastic is
injected into the mold where it fills the mold. The plastic is then
cooled.
[0082] Once the plastic has formed and hardened, the fingers are
drawn from the mold through the openings (apertures
146,147,148,150,160,161,162- ). The knives/punches are drawn
through the upper surface openings 170. Once the knives/punches are
removed, the cut or skived extensions 230,231 disposed between the
leads 130,131 and 131,132 ensures the leads are kept separate. The
molded sensor 112 is then ejected from the mold and any undesirable
openings in the sensor can be sealed closed by the same plastic
used for the mold. In the preferred alternative, the critical
reagents are applied to the sensors in the reaction zone 124 above
the leads. A surfactant can be used to treat the capillary inlet to
facilitate the capillary function. Any extraneous metal projecting
from the sensor can be cut and removed. Then, any desired writings
on the sensor (e.g., manufacturing codes, product name, etc.) can
then be applied to the sensors by conventional means.
[0083] The Third Embodiment
[0084] Shown in FIGS. 13-20 is a third embodiment of an
electrochemical sensor in accordance with the present invention.
These figures use the same reference numbers, but in the 300
series, to identify components that are similar to those in the
previous embodiments. FIGS. 13 and 17, respectively, depict the
sensor 310,310' in its entirety, including its internal components
not normally visible when looking down on the sensor 310,310'.
[0085] In the third embodiment sensor 310, 310' is used in
conjunction with a meter capable of measuring an electrochemical
property of the fluid sample after the fluid sample is drawn into
the reaction zone 324,324'. The sensor 310,310' includes a molded
plastic body 312,312' having a meter attachment end or plug end
314,314' and a fluid sample receiving end 316,316'. The plug end
314,314' is insertable or connectable to a meter, as with the two
prior embodiments. The body also has a bottom surface 313,313' and
a top surface 315,315'. The body 312,312' is molded as a unitary,
single piece having two portions--(a) an electrode-encasing housing
317,317' and (b) an end cap 327,327' pivotably attached to the
electrode housing 317,317' at the fluid sample receiving end
316,316' at hinge 427,427'. In an alternative embodiment, the
electrode housing and the end cap may be separate pieces that are
securedly attachable to one another. The side edges
318,319,318',319' near the plug end 314,314' of the body 312,312'
are tapered so the plug end 314,314' inserts more easily into the
socket cavity of a conventional meter (not shown). The end cap
327,327' may have a "notch" 326,326' formed into the outermost edge
opposite the body to facilitate molding.
[0086] FIG. 15 shows a longitudinal sectional side view of sensor
310. The top surface 315 has three sections or surfaces including
315a,315b,315c. The first top surface 315a accounts for a
predominate portion of the body, as it extends from the plug end
314 to a ledge 415. The second top surface 315b runs from the ledge
415 to the hinge 427, on a plane lower than 315a. The third top
surface 315c extends across one surface of the end cap 327, from
the hinge 427 to the outermost edge of the end cap.
[0087] The hinge 427 allows the end cap to be folded onto the body
so that the third top surface 315c abuts the second top surface
315b, face-to-face, and the edge of the end cap rests substantially
adjacent the ledge 415, as in the second embodiment discussed
above. In the finished sensor, the bottom surface 313a of the end
cap 327 becomes part of the top surface of the body and rests
adjacent the first top surface 315a, in essentially the same plane,
as shown in FIG. 15.
[0088] When the end cap is folded onto the second top surface 315b
of the body, adjacent the terminal end 316 of the body, a channel
termed the "electrochemical reaction zone" 324 forms in the body.
The reaction zone 324 is bound on one side by the second top
surface 315b and, on the opposite side, by top surface of the end
cap 327. The reaction zone has a volume defined by the shape of the
body. Alternatively, if desired, the cap may be shaped so that when
it is pivoted onto the body, the cap defines the volume of the
reaction zone; or the shape of both the cap and the body may form
the volume of the reaction zone.
[0089] Running throughout the longitudinal axis of the body 312 are
the leads 330,331,332, which are spaced apart in fixed relation to
each other. The leads 330,331,332 terminate in the reaction zone
324. FIGS. 17-19 show a sensor in accordance with the invention
having two electrodes 330',331'.
[0090] In the reaction zone or cavity 324, the leads are not
entirely embedded in the insulative material of the body. In the
reaction zone 324, at least a portion of the leads--e.g., the tips,
sides, or other portion--is exposed therein as sensing electrodes
330,331,332 for contacting fluid sample drawn into the body 312.
The reaction zone 324 lies primarily in the bottom lengthwise
portion of the detector. Although the reaction zone may be formed
above or below the electrodes, it is preferably constructed below
the electrodes.
[0091] The cap 327 is folded onto the body and securedly affixed to
the body to form a substantially tight seal. As result of this
configuration, a capillary opening 328 forms in the terminal end
316 of the sensor 310. The capillary opening 328 leads to the
reaction zone 324 where the edges of the sensing electrodes
330,331,332 are exposed to the test fluid. The width of the
capillary opening 328 is approximately the same as that of the
sensing electrodes 330,331,332.
[0092] Body 312 may also have protuberances to ensure correct
alignment of the surfaces when folded about the hinge. The
protuberances are typically disposed on at least one of (a) the
surface of the end cap that folds onto the body and (b) the top
third surface of the body onto which the end cap folds that is
covered by the end cap when folded onto the body. Although a
variety of configurations are possible, in one embodiment, e.g.,
the protuberances may appear on both the end cap and the upper
surface 315b of the body.
[0093] In one embodiment, shown in FIG. 13, the protuberance
comprises a ridge 527 and a recessed surface 528 that mate when the
cap is folded onto the body, to form the reaction zone. In this
embodiment, the ridge 527 may be formed on the second top surface
315b along the periphery of the reaction zone 324, and the recessed
surface may be formed on the cap 327, or vice versa. The ridge 527
may also sit in and be substantially aligned with a secondary ridge
(not shown), which increases the height of ridge 527.
[0094] In the finished sensor 310, the ridge 527 mates with
recessed surface 528 to form a seal, enclosing the reaction zone
324 within the body. Alternatively, the ridge 527 and recessed
surface 528 may be further welded together by, e.g., ultrasonic
energy, adhesive, or any other suitable techniques. The seal, so
formed, prevents the reaction zone 324 from losing fluid or
accepting debris. During welding, the ridge 527 fuses into the
recessed surface 528 without affecting the performance of the
sensor.
[0095] In yet another aspect of the third embodiment, shown in
FIGS. 17-20, the protuberance is an energy director 529' formed on
at least one of the end cap and the upper surface 315b' of the
body. A variety of configurations is possible such as one wherein
the energy director is disposed entirely on the body for fusing
with the cap when pivoting of the cap onto the body. As shown in
the embodiment depicted in FIGS. 17-19, the energy director 529'
typically comprises at least one protruding ridge extending
preferably along the periphery of the end cap. Typically, the
energy director extends along the three unattached sides of the end
cap, although it may extend across portions of the sides. In the
embodiment depicted, the energy director 529' begins at hinge 427'
and extends on the end cap 327' directionally away from the hinge
427' and across the end farthest from the hinge.
[0096] When the cap is pivoted onto the body, the energy director
529' is generally melted by, e.g., ultrasonic energy or other
conventional means, to induce formation of a strong, leak-free
joint bond between the bottom surface and cap surface. The bond so
formed seals the fluid within the chamber, preventing fluid from
diffusing out from the reaction zone. Alternatively, a seal may be
formed by the application of adhesives.
[0097] The sensor of the third embodiment is also a capillary fill
device; i.e., when the capillary opening 328' is placed in contact
with the fluid being tested, the reaction zone 324' draws the fluid
sample into the zone. Included in cap 327' is sample fill vent
368'. When cap 327' is folded onto body 312', at least a portion of
the sample fill vent 368' is in communication with the reaction
zone to form a depressurization vent 378' for releasing air from
the reaction zone as the zone fills with fluid. The
depressurization vent 378' extends between one edge of the sample
fill vent 368' and the ledge 415' of the reaction zone, which is
the back wall of the reaction zone farthest from the terminal end
316'. FIGS. 20a,b show a magnified view of the terminal end portion
of the sensor 310' of FIG. 17. FIG. 20a shows the cap 327' extended
away from the body, and FIG. 20b shows the cap 327' folded onto the
body of the sensor.
[0098] The depressurization vent 378' provides for fill detection
in the third embodiment. Fluid drawn through the capillary opening
328' travels along the capillary, preferably in the lower portion
of the body 312', to the reaction zone 324' where it contacts the
electrodes 331',332' of sensor 310' (or electrodes 330,331,332 of
sensor 330,331,332). Preferably, the surface of the electrodes
facing the upper surface 315' of the body is flush with the bottom
periphery of the capillary inlet 328'. As sample fluid enters the
reaction zone 324', it travels toward the end of the reaction zone
farthest from the capillary inlet until it reaches the
depressurization vent 378'. As the fluid displaces air present in
the depressurization vent 378', the fluid contacts at least one of
the electrodes in the reaction zone, so as to close an open circuit
in the sensor 310' and cause current to flow through the sensor.
The flow of current in the sensor activates the meter, signaling
that the capillary chamber or reaction zone is sufficiently filled
with fluid. The depressurization vent 378' may also be used to
visually detect fluid fill in the reaction zone.
[0099] The injection molded body 312 is constructed of an
electrically insulating injection moldable plastic. The body 312 is
molded around the electrically conductive plate (stamped or cast)
with its leads 330,331,332 so that the conductive plate is encased
primarily within the body 312. The conductive plate is a single
piece of material; it includes the leads 330,331,332 (330',331' in
FIG. 18) and the connecting segments 430 and 431 (reference no. 432
in sensor 310'). After the sensor is made, the segments 430 and 431
interconnecting the leads are cut and/or removed to separate the
leads from one another. If the interconnecting segments remained
intact during operation of the sensor, the system would short
circuit.
[0100] The body may have a plurality of guides molded therein with
at least one of the guides abutting against at least one of the
leads.
[0101] The leads 330,331,332 extend longitudinally through the body
312 from the plug end 314 to the reaction zone 324, terminating
just before the terminal end 316. The leads 330,331,332 are
encased, or embedded, in the body 312 at a pre-determined distance
from each other; they are generally parallel to one another though
this is not necessary for operation of the sensor. In the reaction
zone, a sufficient portion of the leads are exposed for contacting
the fluid sample; the exposed portion includes, e.g., at least the
tips, ends, or sides of the electrodes.
[0102] The electrodes 330,331,332 are an electrically conductive
material such as metal or metal alloy; e.g., platinum, palladium,
gold, silver, nickel, nickel-chrome, stainless steel, copper or the
like. For enhanced performance and sensitivity, they may also be
coated with a metal different from that composing the lead; e.g., a
lead made of copper may be coated with gold. If desired, the width
of the leads 330,331,332 may be widened or narrowed in the reaction
zone 324 to expose more or less surface area to the fluid and
chemicals therein. The leads 330,331,332 extending through the body
can be as wide as the exposed portion within the reaction zone,
which comprises the electrodes 330, 331, 332.
[0103] Each of the leads 330,331,332 terminates in a segment
333a,b,c that may extend outside the body 312 from the plug end 314
where the leads provide surface areas 334,335,336, respectively,
for contact with the meter (not shown). Alternatively, the leads
can be embedded in the molded plastic such that only a portion of
each lead is exposed outside the body at the plug end 314; or the
top surface of the leads comes in contact with the meter electrical
contact leads.
[0104] Apertures molded into the top surface 315 and the bottom
surface 113 of the body 312 permit fingers to be inserted into and
removed from the mold during the molding process. The top surface
315a has two sets of apertures--first apertures 346 and second
apertures 347--each having three individual openings or apertures.
The bottom surface 313 has third aperture 348, fourth aperture 350,
and fifth apertures, the latter including three individual
apertures 360,361,362. Once the molding is completed, each of these
apertures 346,347,348,350 is preferably left open. In a preferred
embodiment, the apertures are closed to prevent accidental contact
of the fluid with areas other than the electrodes in the reaction
zone. The apertures may, alternatively, be covered such as with the
same or a different material used in the molding process.
[0105] Within the reaction zone 324, conductive electrodes 330,
331, 332 include a primary working electrode 352, a reference or
counter electrode 353, and a secondary working electrode 354. In
the reaction zone, the conductive electrodes 330, 331, 332 contact
the test sample, in fluid form, as it enters the sensor 310. The
signal carried by the electrodes arises in the reaction zone 324
from contact made by the exposed portion of the electrode with the
test sample. In the reaction zone, one electrode, preferably the
center electrode is a reference electrode. The reaction zone may
also have one or, alternatively, two working electrodes; e.g.,
primary working electrode 352 and secondary electrode 354.
[0106] An enzyme, conjugated to another moiety, such as an antibody
or antigen or an analyte, is applied to the outer surface of the
primary working electrode 352, and if desired, an electron transfer
mediator may be applied to the same electrode 352. An antibody may
also be applied to the outer surface of the secondary working
electrode 354 or otherwise present in the reaction zone. As such,
the reaction zone 324 can contain antibodies, enzyme-antibody
conjugates, enzyme-analyte conjugates, and the like.
[0107] The enzyme can be applied to the entire exposed surface of
the primary electrode 352 or the secondary electrode 354.
Alternatively, the enzyme is applied to a particular, defined
portion of a working electrode. Or, an enzyme can be applied to all
the electrodes 352,353,354 in the reaction zone 324. Preferably,
one of the working electrodes (352 or 354) is selectively coated
with the enzyme carrying a reagent with the enzyme, and the other
working electrode (354 or 352) is coated with a reagent lacking the
respective enzyme.
[0108] In yet another aspect of this third embodiment, the reaction
zone or cavity 324 may itself be coated with a substance--such as a
reagent, an antibody, or an enzyme--that reacts with certain
constituents in the fluid sample to change the electrochemical
properties of the sample. The resulting change is readily detected
by the electrodes and measured by the meter.
[0109] The Molding Process of the Third Embodiment
[0110] The mold has the shape of the body 312. The conductive
330,331,332 leads (in the form of a composite plate with the
joining extensions 430,431 for interconnecting the electrodes) are
first treated or coated with a substance, which may be an enzyme,
an antibody, or a chemical reagent, as examples. The
chemicals/reagents (with and without enzymes) are generally applied
after the molding.
[0111] The plate is fed into the mold and placed on or between
fingers (not shown) that project into the mold through the openings
in the mold, which correspond to the apertures 346,347,348,350,
360,361,362. The fingers hold the plate in place, keeping it level
during the set-up and molding process.
[0112] Knives or punches (not shown) are inserted through the top
surface of the mold (outline of opening formed by the
knives/punches 370). These knives punch and sever the joining
extensions 430,431 and hold the bent portions in place during
molding, as shown in FIG. 15. During the molding process, the
bottom apertures allow the fingers to be projected into the mold to
support the plate with leads; similarly, the top apertures allow
the fingers to be projected into the mold to hold the plate in
place with the leads. Liquid plastic is injected into the mold,
filling it. The plastic is then cooled.
[0113] After the plastic has formed and hardened sufficiently, the
fingers are removed from the mold through the openings; i.e.,
apertures 346,347,348,350,360,361,362. The knives/punches are drawn
through and removed from the upper surface openings 370, leaving
the cut or skived extensions 430,431 disposed between the leads
330,331 and 331,332. These cut extension keep the leads separated.
The molded sensor 312 is then ejected from the mold, and any
undesirable openings in the sensor can be sealed closed with the
same plastic used for the mold.
[0114] In a preferred alternative, the critical reagents are
applied to the sensor in the reaction zone 324 above the leads. A
surfactant can also be applied to the capillary opening 328 to
facilitate the capillary function. Any extraneous metal projecting
from the sensor can be cut and removed. In addition, any desired
writings or other designations on the sensor (e.g., manufacturing
codes, product name, etc.) can be applied to the sensors by
conventional means.
[0115] While the specific embodiments have been illustrated and
described, numerous modifications come to mind without
significantly departing from the spirit of the invention and the
scope of protection is only limited by the scope of the
accompanying claims. For instance, in another embodiment of the
present invention, a sensor is designed for use with a light
reflectance measuring meter for photometric detection of a dye
contained within a fluid sample receiving well.
* * * * *