BIOSENSOR HAVING NANOSTRUCURED ELECTRODES
FIELD OF THE INVENTION
The present invention relates to an electrochemical immunoassay based microfluidic
device. More particularly, the present invention relates to a substrate for the
microfluidic device for detecting target analytes in a biological or chemical assay.
BACKGROUND AND PRIOR ART
Microfluidic s devices, first developed in the early 1990s, were initially fabricated in
silicon and glass using photolithography and etching techniques adapted from the
microelectronics industry, which are precise but expensive and inflexible. The trend
recently has moved toward the application of soft lithography-fabrication methods
based on printing and molding organic materials. Microfluidics refers to a set of
technologies that control the flow of minute amounts of liquids or gases, typically
measured in nano- and picoliters- in a miniaturized system. "Unlike microelectronics,
in which the current emphasis is on reducing the size of transistors, microfluidics is
focusing on making more complex systems of channels with more sophisticated fluid
handling capabilities", says George Whitesides, Mallinckrodt Professor of Chemistry
and Chemical Biology at Harvard University.
A microfluidic device can be characterized as having one or more channels
with at least one dimension less than 1 mm. The common fluids used in microfluidic
devices include whole blood samples, bacterial cell suspensions, protein or antibody
solutions and various buffers. The microfluidic devices can be used to obtain a variety
of interesting measurements including molecular diffusion coefficients, fluid
viscosity, pH, chemical binding coefficients and enzyme reaction kinetics. Other
applications for microfluidic devices include capillary electrophoresis, isoelectric
focusing, immunoassays, flow cytometry, sample injection of proteins for analysis via
mass spectrometry, PCR amplification, DNA analysis, cell manipulation, cell
separation, cell patterning and chemical gradient formation. Many of these
applications have utility for clinical diagnostics.
In recent years, miniaturization of chemical and biochemical tools has become
an expanding field. The use of microfluidic devices to conduct biomedical research
and create clinically useful technologies has numerous significant advantages. The
main factors encouraging the development of microfluidic devices are the desire for
decreased analyte consumption, rapid analysis and improved automation capacity.
The need to limit analyte consumption is highlighted by the increasing number of
assays that are performed, the use of reactants for analysis requiring to be kept as
small as possible in order to reduce costs but also to limit waste production.
Also, conventional assays require samples to be taken and then transferred to a
laboratory. The newer devices provide hand held devices which can be used for
conducting assays without the need of laboratory instruments.
European Patent Application Publication No. 1391241 discloses a microfluidic device
for the detection of target analytes. The microfluidic device employs a solid support,
which has a sample inlet port, a storage chamber and a microfluidic channel,
connecting the solid support with the sample inlet port and the storage chambers. The
printed circuit boards are used as solid supports on which detection electrodes are
provided. The detection electrodes are provided by self assembled monolayers, which
are specific to a particular substrate, for instance thiols.
PCT Application Publication No. WO2010020574 discloses a microfluidic system for
assaying a sample, especially a biological sample. The microfluidic system is
configured to allow two samples, such as a test sample and a control, to be processed
under the same reaction conditions without cross contamination. The invention also
relates to a cartridge system comprising the microfluidic system, and to assays
performed using the microfluidic system or cartridge system. The microfluidic system
comprises two reaction reservoirs, a reagent delivery channel to deliver reagents to the
reaction reservoirs, a waste channel, and a means for retaining one or more reagents in
each reaction zone, such as magnetic or magnetisable. The reservoirs are connected to
waste chambers. The reservoirs have interconnected chambers which store processing
components and sample preparation components. Thus, the apparatus is complex with
too many interconnections.
US Patent No. 7,419,821 discloses a single use disposable cartridge for the
determination of an analyte in biological samples using electrochemical
immunosensors or other ligand/ligand receptor based biosensors. The cartridge
comprises a cover, a base, and a thin film adhesive gasket, which is disposed between
the base and the cover. The analyte measurements are performed in a thin-film of
liquid coating an analyte sensor and such thin-film determination are performed
amperometrically. The cartridge comprising an immunosensor is microfabricated
from a base sensor of an unreactive metal such as, gold, platinum or iridium.
PCT Application Publication No. WO2004/061418 describes a cartridge for
performing a plurality of biochemical assays. The cartridge comprises a flow cell
having an inlet, an outlet and a detection chamber. The inlet, outlet and detection
chamber define the flow path through the flow cell. The detection chamber comprises
plurality of electrodes involving a dedicated working electrode, a dedicated counter
electrode and two or more dual-role electrodes, wherein each of the dual-role
electrodes is used as a working electrode for measuring an assay dependent signal,
and subsequently as a counter electrode for measuring a different assay dependent
signal at a different one of said plurality electrode. The fluidic network is formed
within the cartridge employing fabrication method appropriate to the cartridge body
material, such as stereolithography, chemical/laser etching, integral molding,
machining, lamination, etc.
The microfluidic devices available in the market are manufactured by using
micromachining and milling techniques, hence, the microfluidic devices are
expensive. Thus, there is a need to develop an inexpensive, hand-held miniature assay
device, which can analyze one or more target analytes with high sensitivity and
specificity and which provides qualitative as well as quantitative measurements at low
concentrations of analytes.
SUMMARY OF THE INVENTION
The present invention provides a point-of-care, self calibrated, self contained hand
held device for rapid screening and diagnosis of various disease markers.
The present invention provides a substrate for a microfluidic device comprising a
polymeric base plate; at least one sensor formed over the polymeric base plate for
detecting at least one target analyte contained in a sample, wherein the sensor
comprising at least one working electrode and at least one reference electrode; a
plurality of nanostructures deposited over the working electrode and a recognition
element bound to or deposited over the nanostructures.
The present invention also provides a microfluidic device comprising the substrate,
wherein the substrate acts as a bottom layer for the microfluidic device and an
electrochemical sensor.
The present invention also provides a microfluidic device, wherein the microfluidic
device of the invention further comprises a reagent component comprised of at least
one entry point for a sample containing at least one analyte, at least one reservoir for
storing reagent and a waste chamber for disposing the used reagent; and a gasket for
adhering the substrate to the reagent component.
BRIEF DESCRIPTION OF THE DRAWINGS
To further clarify the above and other advantages and features of the present
invention, a more particular description of the invention will be rendered by reference
to specific embodiments thereof which are illustrated in the appended drawings. It is
appreciated that these drawings depict only illustrated embodiments of the invention
and are therefore not to be considered limiting of its scope. The invention will be
described and explained with additional specificity and detail through the use of
accompanying drawings in which:
Figure 1 illustrates a schematic view of a substrate for a microfluidic device in
accordance with an embodiment of the present invention.
Figure 2 illustrates a schematic sectional view of a gasket adhered to a substrate for a
microfluidic device in accordance with an embodiment of the present invention.
Figure 3 illustrates an isometric view of a microfluidic device according to an
embodiment of the present invention.
Figure 4 illustrates a standard graph of the current generated (at 0.2 sec) in an
amperometric measurement of the product produced versus the HbAlc percentage.
Together with the following description, the figures demonstrate and explain the
principles of the microfluidic devices and methods for using the microfluidic devices
in biological or chemical assay. The thickness and configuration of components of
microfluidic device, illustrated in the figures, may be expanded for clarity. The same
reference numerals in different figures represent similar, through necessarily identical
components.
DETAILED DESCRIPTION OF THE INVENTION
DEFINITIONS
Before describing the present invention in detail, it has to be understood that
this invention is not limited to particular embodiments described in this application. It
is also to be understood that the terminology used herein is for the purpose of
describing particular embodiments only and is not intended to be limiting.
As used in the specification and claims, singular terms including, but not
limited to, "a", "an" and "the" include plural references unless the context clearly
indicates otherwise. Plural terms include singular references unless the context clearly
indicates otherwise. Unless defined otherwise, all technical and scientific terms used
herein have the same meaning as commonly understood by one of the ordinary skill in
the art to which the invention belongs.
According to this invention, the term "nanostructures" refers to structures that
possess the nanometer size and has partial or complete nanometer effect (e.g. surface
effect, size effect).
According to this invention, the term "nanoparticles (NPs)" refers to solid
particles, which, in three-dimensional space, have at least one-dimensional size less
than 500 nm, preferably less than 100 nm, optimally less than 50 nm.
According to this invention, the term "nanotubes (NTs)" specifically refers to
hollow-core nanostructures with a diameter less than 10 nm.
According to this invention, the term "target analyte" refer to a specific
material, the presence, absence, or amount of which is to be detected, and that is
capable of interacting with a recognition element. The targets that may be detected
include, without limitation, molecules, compounds, complexes, nucleic acids,
proteins, such as enzymes and receptors, viruses, bacteria, cells and tissues and
components or fragments thereof. Exemplary, samples containing target analyte
includes, without limitation, whole blood sample, serum, urine, stool, mucus, sputum
and tissues etc.
The invention described herein is explained using specific exemplary details for better
understanding. However, the invention disclosed can be worked on by a person
skilled in the art without the use or by obvious modification in the specific details as
discussed herein below.
While this invention has been described as having a specific design, the present
invention can be further modified within the spirit and scope of this disclosure. This
application is therefore intended to cover any variations, uses, or adaptations of the
invention using its general principles. Further, this application is intended to cover
such departures from the present disclosure as appear within known or customary
practice in the art to which this invention pertains.
The present invention relates to a substrate for a microfluidic device, comprising a
polymeric base plate; at least one sensor formed over the polymeric base plate for
detecting at least one target analyte contained in a sample, wherein the sensor
comprises at least one working electrode and at least one reference electrode; a
plurality of nanostructures deposited over the working electrode; and a recognition
element bound to or deposited over the nanostructures. The nanostructures deposited
over the working electrode for increasing the surface area of the working electrode.
The Figure 1 illustrates a substrate (denoted by the numeric 100) for a microfluidic
device.
In an embodiment of the present invention, the substrate (100), as represented in
Figure 1 comprises a polymeric base plate (denoted by the numeric 110) and a sensor
(denoted by the numeric 120), which is formed over polymeric base plate for
detecting target analyte contained in a sample.
In accordance with an embodiment of the present invention, the polymer used in the
polymeric base plate (110) is selected from polyester, polystyrenes, polyacrylamides,
polyetherurethanes, polysulfones, polycarbonates or fluorinated or chlorinated
polymers such as polyvinyl chloride, polyethylenes and polypropylenes. Other
polymers include polyolefins such as polybutadiene, polydichlorobutadiene,
polyisoprene, polychloroprene, polyvinylidene halides, polyvinylidene carbonate, and
polyfluorinated ethylenes. The copolymers, including styrene/butadiene, alpha-methyl
styrene/dimethyl siloxane, or other polysiloxanes such as, polydimethyl siloxane,
polyphenylmethyl siloxane and polytrifluoropropylmethyl siloxane may also be used.
Other alternatives include polyacrylonitriles or acrylonitrile containing polymers such
as poly alpha-acrylanitrile copolymers, alkyd or terpenoid resins, and polyalkylene
polysulfonates. However, the material used for forming the polymeric base plate is
not limited to those materials listed above and can be any material which has chemical
and biological stability and processability.
In accordance with an embodiment of the present invention, the sensor includes at
least one working electrode, at least one reference electrode and optionally a counter
electrode. These electrodes are formed over metal coated polymeric base plate by
using a laser technique, such as laser ablation. According to an embodiment of the
present invention, the metals are coated over the polymeric base plate (110) by
sputtering technique. The sensor may also be formed over polymeric base plate using
a screen printing technique. However, it may be apparent to a person skilled in the art
to replace sputtering with any other suitable technique known in the art.
In accordance with an embodiment of the present invention, the noble metal coated
over the polymeric base plate is selected from gold, platinum or palladium. According
to an embodiment of the present invention, the polymeric base plate (110) is sputtered
with gold and the sensors are ablated with laser technique over the base plate (110).
Alternatively, the sensors are printed on polymeric base plate using screen printing.
In accordance with an embodiment of the present invention, the sensor (120)
including the working electrode is deposited with a plurality of nanostructures, which
increases the surface area of the working electrode. The increase in surface area of the
working electrode increases the sensitivity and accuracy of the assay to be performed
even with very low quantities of target analyte. The non-limiting exemplary
nanostructures according to the present invention are selected from carbon nanotubes
(CNTs) or gold nanoparticles.
In accordance with an embodiment of the present invention, the nanostructures are
gold nanoparticles deposited over the working electrode using the electro deposition
technique. In an embodiment, the nanostructures are carboxylated carbon nanotubes
and the percentage of carboxylation of carbon nanotubes is 3% to 5%.
In accordance with an embodiment of the present invention, the working electrode
(120) of the sensor is ablated in the form of concentric arcs, circle, spiral, helix or any
polygonal shape to increase the deposition of nanostructures. The "polygonal"
shape is a multi-sided, closed planar shape. The Polygons may include trigons (or
triangles), tetragons (or quadrilaterals), pentagons, hexagons, heptagons, octagons,
and the like. Tetragons may include squares and rectangles, which have four sides
connected at four right angles. Tetragons also may include rhombi (e.g. diamondshaped
polygons or parallelograms), which do not include four right angles.
According to an embodiment of the present invention, the working electrode is
ablated in the form of concentric arcs. The concentric arcs of the working electrode
are in a hill-valley type arrangement providing better deposition of the nanostructure.
The working electrode has a diameter in the range of 2mm to 8mm.
The nanotubes deposited working electrode are further bound to or deposited with a
recognition element. The recognition element is bound to nanotubes using coupling
chemistry, such as the l-ethyl-3-(3-dimethylaminopropyl)carbodiimide/Nhydroxysuccinimide
(EDC/NHS) coupling chemistry. The non-limiting examples of
the recognition element are antigens, antibodies, enzymes, aptazymes and aptamers.
In accordance with an embodiment of the present invention, the target analyte
containing sample is selected from the group comprising of whole blood, serum and
urine.
In accordance with an embodiment of the present invention, the substrate optionally
comprises at least one fluid detection sensor formed over the polymeric base plate for
detecting the presence of the analyte and at least one reagent involving reading
reagent or reaction reagent.
The reading reagent is the electrochemical substrate solution such as napthyl
phosphate that is used in the Enzyme-Linked Immunosorbent Assay (ELISA). The
reaction reagent is a reagent comprising of conjugate or secondary antibody that is
enzyme labeled that is used in the ELISA.
Chronoamperometry is an electrochemical technique of measurement whereby
appropriate voltage is applied across the working and reference electrodes and the
resulting current for the electrochemical reaction is measured between the working
and reference electrode.
The present invention also relates to a microfluidic device comprising a substrate
according to the present invention, a reagent component and a gasket for adhering the
substrate to the reagent component.
In accordance with another embodiment of the present invention, the microfluidic
device (denoted by the numeric 300) represented in Figure 3. The substrate (100) of
the microfluidic device serves dual purpose, wherein the substrate acts as a bottom
layer for the microfluidic device and also as an electrochemical sensor.
In accordance with another embodiment of the present invention, the Figure 2
represents a gasket which adheres the substrate (100) to the reagent component.
According to the present invention, the gasket is a double sided pressure sensitive
adhesive. The gasket is laser cut to define the fluidic path of the sample and the
reagents from the component to the sensor (120) of the substrate (100) through
microfluidic channels on the substrate. The gasket acts as a spacer between the
reagent component and the substrate along with the microfluidic channels for the flow
of the sample. The thickness of the gasket is between IOOmih to 400mih . In an
embodiment of the present invention the thickness of the gasket is > 200mih . The flow
of the sample (denoted by the numeric 210), the reagents through the microfluidic
channels on the substrate and the gasket is through capillary action.
In accordance with another embodiment of the present invention, the used reagents
and the sample is then dispensed to the waste chamber in the microfluidic device
through a dump (denoted by the numeric 240).
The connector region of the substrate (denoted by the numeric 250) facilitates the
positioning of the substrate in the microfluidic device in the slot of the microfluidic
device.
The substrate (100) adhered to a gasket on one side shown in Figure 2 is positioned in
a slot provided for the substrate in the reagent component (denoted by the numeric
310). The reagent component comprises an entry point (denoted by the numeric 315)
for a sample containing at least one target analyte, a reservoir for storing a reagent
(denoted by the numeric 320), and a waste chamber (denoted by the numeric 325) for
disposing the used reagent.
The Figure 3 representing the microfluidic device contains two reservoirs, first
reservoir (320) and second reservoir on the other side of the first reservoir; one
reservoir is for storing reaction reagent and other one is for storing a reading reagent.
The first and the second reservoirs are formed by a partition which separates the
reaction reagent from the reading reagent. However, there can be more than one
reaction reagent and reading reagent based on the type of assay to be performed.
Additionally, there may be more than one reservoir for storing reaction reagents. The
present invention is not restricted to the number of reservoirs or to the location of the
reservoirs. The arrangements may vary according to the assay to be performed which
will be apparent to a person skilled in the art.
In accordance with another embodiment of the present invention, the microfhiidic
device further comprises at least one conduit for dispensing the reagents from the
reservoir to the substrate. The microfhiidic device as shown in Figure 3 comprises two
conduits, one each for dispensing the reaction reagent and the reading reagent to the
substrate. First conduit (denoted by the numeric 330) is used to dispense the reaction
reagent from the first reservoir (320) to the substrate and second conduit is positioned
behind the first conduit and is used to dispense the reading reagent from the second
reservoir to the substrate.
In accordance with another embodiment of the present invention, the microfhiidic
device further comprises compressed air entry septa (denoted by the numeric 335)
which are pierced with a needle. The compressed air displaces the reagents stored in
the reservoirs and allows the reagents to flow through the conduits into the substrate.
In accordance with another embodiment of the present invention, the microfhiidic
device further comprises holes in the reagent chamber, where the substrate is
positioned (denoted by the numeric 305) for entry of the sample (denoted by the
numeric 340), the reaction reagent (denoted by the numeric 345) and the reading
reagent (denoted by the numeric 350).
In accordance with another embodiment of the present invention, the sample
containing the target analyte, the reaction reagent and the reading reagent flow
through the holes in the reagent chamber to the sensor(s) present on the substrate
through the microfhiidic channels provided by the gasket. The target analyte present
in the sample binds to the recognition element bound on the nanostructures and a
signal is generated, which may be used to detect the analyte quantitatively and/or
qualitatively. The method for detection of the target analytes will vary depending on
the type of assay and can be easily apparent to a person skilled in the art.
In accordance with embodiments of the present invention, it is possible to detect
multiple target analytes from a sample. The recognition elements will be selected
based on the target analytes of interest.
In accordance with the present invention the "recognition element" refers to any
chemical, molecule or chemical system that is capable of interacting with a target
molecule. The recognition elements can be, for example and without limitation,
antibodies, antibody fragments, peptides, proteins, glycoproteins, enzymes, nucleic
acids such as oligonucleotides, aptamers, DNA, cDNA and RNA, organic and
inorganic molecules, sugars, polypeptides and other chemicals.
In accordance with embodiments of the present invention, the microfluidic device of
the present invention is self-calibrated. Each sensor on the substrate is pre-calibrated
and the calibration value(s) is mentioned over the device.
According to a further embodiment, the invention relates to use of the microfluidic
device to perform at least one of chemical and biological analysis.
According to an embodiment, the microfluidic device is used to perform
immunoassays.
An immunoassay combines the principles of chemistry and immunology for a specific
and sensitive detection of the analytes of interest. The basic principle of this assay is
the specificity of the antibody-antigen reaction. The analytes in biological liquids
(samples) such as serum or urine are frequently assayed using immunoassay methods.
In essence, the method depends upon the fact that the analyte in question is known to
undergo a unique immune reaction with a second substance, which is used to
determine the presence and amount of the analyte. This type of reaction involves the
binding of one type of molecule, the antigen, with a second type, the antibody.
Immunoassay is widely used to detect analytes using antibodies. Most immunoassays
are heterogeneous: the antigen-antibody complex is bound to a solid substrate, and
free antibodies are removed by washing. In homogeneous immunoassays, the free and
bound antibodies do not need to be separated via a solid substrate. These types of
procedures minimize washing steps and fluid handling, but they require that the free
and antigen-bound antibodies exhibit different electrophoretic mobilities.
Miniaturization of homogeneous immunoassays offers advantages, but more work has
been done on the miniaturization of heterogeneous immunoassays than of
homogeneous immunoassays.
The radioimmunoassay, using radioactively labeled antigens or antibodies was the
only preference available for conducting immunoassay before the development of
Enzyme-Linked Immunosorbent Assays (ELISAs). Elisa is a popular format of a
"wet-lab" type analytic biochemistry assay that uses one sub-type of heterogeneous,
solid-phase enzyme immunoassay (EIA) to detect the presence of a substance in a
liquid sample or wet sample. Elisa' s are typically performed in 96-well or 384-well
polystyrene plates, which will passively bind antibodies and proteins. It is his binding
and immobilization of reagents that makes elisa so easy to design and perform. The
reactants of the elisa immobilized to the microplate surface makes it easy to separate
bound from non-bound material makes the elisa a powerful tool for measuring
specific analytes within a crude preparation.
Thus, the method for preparation of sensor, immobilized with the capture antibody for
the analysis is briefly described herein below:
Step I: Cleaning of sensors
The laser ablated sensors were cleaned using a gold cleaning solution (GCS). For
cleaning, the sensors were dipped in GCS:DI water (1:1) solution for 5 minutes and
were then rinsed thoroughly with demineralized water (DI water).
Step II: Coating of sensor by conduction agent i.e. drop casting of COOH-CNTs on
the gold sputtered sensor surface
Multi-walled carboxylated carbon nanotubes (COOH-CNTs) solution was prepared
by adding COOH-CNTs in O.IM diethanolamine buffer to get a final concentration of
20mg/ml. The 6m1 of COOH-CNTs solution was drop casted on the sensor gold
surface (which is used as reference electrode). The COOH-CNTs was dried at 60°C
for 10 minutes.
Step III: Immobilization of capture Mc Hb
Capture antibody (Monoclonal antiHb) was immobilized on the COOH-CNTs through
EDC-NHS coupling. Initially the COOH-CNTs surface was activated by treating it
with EDC-NHS for 30 minutes followed by addition of 30m1 of capture antibody (50
mcg/ml). The antibody immobilization was carried out for 3 hours at room
temperature. Blocking was done using Stabilcoat or 1% BSA for 30 minutes at room
temperature. Excess Stabilcoat was removed, washed with phosphate buffer and were
stored at 2-8°C under N2 atmosphere, till further use.
EXAMPLES
Preparation of the substrate for microfluidic device
A polymeric base plate of polyester was sputtered with gold. The sensors comprising
working electrodes, reference electrodes and a counter electrode were formed over the
polymeric base plate using laser ablation. The working electrodes were formed in the
shape of concentric arcs of 2mm to 8mm diameter. A solution (3-5m1) containing
CNTs was poured over the sensors and the solution was allowed to dry. The CNTs
bound to the working electrodes, wherein the carboxyl groups of the CNTs coupled to
the recognition element, for instance HbAlc antibodies using coupling chemistry. The
substrate was fitted in the microfluidic device via the connector.
HbAlc Testing using the microfluidic device
A diluted blood sample (100 mΐ ) (luL of blood sample diluted to 100 mΐ by Mfr.
diluent) was poured to the microfluidic device containing the substrate. The blood
sample containing the HbAlc antigens was allowed to flow in the microfluidic
channels by capillary action and react with HbAlc antibodies already present on the
substrate, which are coupled to the carboxylated nanotubes. The blood sample was
allowed to incubate for 5 minutes after which the reaction reagent was pumped by
means of a micro solenoid pump. Then the reading reagent was pumped to take the
electrochemical reading. The fluid detection sensors present on the substrate let the
device know that blood sample or the reaction reagent or reading reagent were present
in front of the electrochemical sensors.
Measurement of HbAlc
Using HbAlc Controls
2m1 of the HbAlc Controls such as, LI (4.78% concentration of HbAlc), L2 (7.37%
concentration of HbAlc) is mixed with 198m1 of the lysing agent. ImM Cetyl
trimethylammonium bromide (CTAB) prepared in phosphate buffer is used in this
case.
Using Whole Blood samples
2m1 of the whole blood sample is mixed with 198m1 of the lysing agent. ImM CTAB
prepared in phosphate buffer is used in this case.
50m1 of the diluted sample was added on the sensor and incubated for 5 minutes at
room temperature.
The sensors were washed twice with PBT (Phosphate Buffer pH 7.0 with 0.002 %
Tween-20).
30m1 of conjugated secondary antibody (10 mcg/ml Mc HbAlc) was added on the
sensor and was incubated for 5 minutes at room temperature.
The sensors were then washed twice with PBT (Phosphate Buffer pH 7.0 with 0.002
% Tween-20).
50m1 of the substrate, lOmM para-napthyl phosphate was added on the sensors and
was incubated for 2 minutes at room temperature.
Amperometric measurement of the product produced (napthol) was recorded.
A standard graph of the current generated (at 0.2 sec) versus the HbAlc % was
plotted in Figure 4.
Controls-HbAlc % Avg. Current at 0.2 sec (mA)
4.78 13.930
7.37 17.620
11.1 28.565
15.1 32.910
The microfluidic device of the present invention is a self-calibrated, self contained
hand-held device for rapid screening and diagnosis of various disease markers. It is
also a high performance device in terms of sensitivity and specificity, which adds an
advantage of quantitative measurements of low concentrations of disease markers in
whole blood/serum. Moreover, the device of the present invention is inexpensive as
it does not require any micro-processing for production of the device. The device of
the present invention is a "Lab on a cartridge" as it performs all the functions of a
laboratory instruments.
In the above description, certain specific details of disclosed embodiments such as
specific materials, designs etc. are set forth for purposes of explanation rather than
limitation, so as to provide a clear and thorough understanding of the present
invention. However, it should be understood readily by those skilled in this art, that
the present invention may be practiced in other embodiments without departing from
the spirit and scope of this disclosure which is illustrated by the appended claims.
WE CLAIM:
1. A substrate for a microfluidic device, comprising:
a polymeric base plate;
at least one sensor formed over the polymeric base plate for detecting at least one
target analyte contained in a sample,
wherein the sensor comprising at least one working electrode and at least one
reference electrode; a plurality of nanostructures deposited over the working
electrode for increasing the surface area of the working electrode, and
a recognition element bound to or deposited over the nanostructures.
2. The substrate as claimed in claim 1, wherein the polymeric base plate is metal
coated.
3. The substrate as claimed in claim 2, wherein the sensor is formed over the metal
coated polymeric base plate using laser ablation.
4. The substrate as claimed in claim 2, wherein the polymeric base plate is coated
with the metal by sputtering.
5. The substrate as claimed claim 4, wherein the polymeric base plate is coated with
a metal selected from the group consisting of noble metals such as gold,
palladium or platinum.
6. The substrate as claimed in claim 1, wherein the sensor is formed over the
polymeric base plate using screen printing.
7. The substrate as claimed in claim 1, wherein the polymeric base plate is made
using a polymer; wherein the polymer is selected from polyester, polystyrenes,
polyacrylamides, polyetherurethanes, polysulfones, polycarbonates or fluorinated
or chlorinated polymers such as polyvinyl chloride, polyethylenes or
polypropylenes.
8. The substrate as claimed in claim 1, wherein the working electrode is in the form
of concentric arcs, circle, spiral, helix or polygonal shape.
9. The substrate as claimed in claim 8, wherein the working electrode is in the form
of concentric arcs.
10. The substrate as claimed in claim 9, wherein the concentric arcs of the working
electrode are in a hill-valley type arrangement.
11. The substrate as claimed in any one of claims 1 or 8, wherein the working
electrode has a diameter in the range of 2mm to 8mm.
12. The substrate as claimed in claim 1, wherein the nanostructures are selected from
carbon nanotubes or gold nanoparticles.
13. The substrate as claimed in claim 12, wherein the gold nanoparticles are
deposited over the working electrode by electro deposition.
14. The substrate as claimed in claim 12, wherein the carbon nanotubes are
carboxylated.
15. The substrate as claimed in claim 14, wherein the percentage of carboxylation of
the carbon nanotubes is 3% to 5%.
16. The substrate as claimed in claim 1, wherein the recognition element is selected
from the group consisting of antigens, antibodies, enzymes, aptazymes, or
aptamers.
17. The substrate as claimed in claim 1, wherein the sensor optionally comprises
counter electrode.
18. The substrate as claimed in any one of claims 1 to 17, wherein the substrate
optionally comprises at least one fluid detection sensor formed over the
polymeric base plate for detecting the presence of the sample and at least one
reading reagent and reaction reagent.
19. A microfhiidic device comprising:
a substrate as claimed in any one of the claims 1-18;
a reagent component comprising at least one entry point for a sample
containing at least one target analyte, at least one reservoir for storing a
reagent and a waste chamber for disposing used reagent; and
a gasket for adhering the substrate to the reagent component, wherein the
gasket defines a fluidic path of the sample and the reagent from the reagent
component to the sensor of the substrate.
20. The microfhiidic device as claimed in claim 19 further comprising at least one
conduit for dispensing the reagent from the reservoir to the substrate.
21. The microfhiidic device as claimed in claim 19, wherein said substrate acts as
electrochemical sensor and a bottom layer for the microfhiidic device.
22. The microfhiidic device as claimed in claim 19, wherein the gasket is a double
sided pressure sensitive adhesive.
23. The microfhiidic device as claimed in claim 22, wherein the gasket is laser cut to
define the fluidic path.
24. The microfhiidic device as claimed claim 19, wherein the thickness of the gasket
is between IOOmih to 400mih for free flowing of the sample through the fluidic
path.
25. The microfhiidic device as claimed in claim 24, wherein the thickness of the
gasket is >200 mih .
26. The microfhiidic device as claimed claim 19, wherein the sample containing
target analyte is selected from whole blood, serum or urine.
27. The microfhiidic device as claimed in claim 19, wherein the device is precalibrated
and the calibration value is mentioned over the device.
28. The microfhiidic device as claimed in any one of claims 19 to 27 used to carry
out at least one of chemical and biological analysis.
29. The microfhiidic device as claimed in claim 28, wherein the device is used to
carry out immunoassays.