Microfluidic Glucose SensorMicrofluidic Glucose SensorSenior Design Group 4Senior Design Group 4

Kristen JevsevarKristen JevsevarJason McGillJason McGill

Sean MercadoSean MercadoRebecca TarrantRebecca Tarrant

Advisor: Dr. John Wikswo, Dr. David CliffelGraduate Advisor: Jennifer Merritt

Problem StatementProblem Statement

Primary ObjectivePrimary ObjectiveQuantify glucose consumption/production on Quantify glucose consumption/production on

a microliter scalea microliter scaleDesign a glucose electrode interface that will Design a glucose electrode interface that will

measure micro-scale concentrations while measure micro-scale concentrations while maintaining affordabilitymaintaining affordability

Long Term GoalLong Term GoalExtend the design to measure lactate, Extend the design to measure lactate,

oxygen, and pHoxygen, and pH

Diabetic ApplicationsDiabetic Applications Inexpensive glucose monitors Inexpensive glucose monitors

are regularly used by diabetics.are regularly used by diabetics. Our device will not be used in Our device will not be used in

diabetic diagnostics.diabetic diagnostics. However, biological researchers However, biological researchers

may use similar techniques to may use similar techniques to study cellular metabolism and study cellular metabolism and toxicology.toxicology.

ApplicationsApplications Currently, researchers measure

extracellular metabolites, such as glucose, on a millileter scale.

Microfluidics work on micro and Microfluidics work on micro and nanoliter scales.nanoliter scales.

Smaller volumes yield faster and Smaller volumes yield faster and more accurate results.more accurate results.

Less expensive and easily Less expensive and easily reproducible reproducible

Provides near real time resultsProvides near real time results

Similar SystemsSimilar Systems

Specially designed electrodes already exist that are able to measure glucose concentrations.

To date, there are very few ways to simultaneously measure glucose, lactate, oxygen, pH and other metabolites easily and inexpensively.

Using a readily produced electrode, it is possible to easily measure glucose levels on a small scale.

This technology can then be extended to multiple metabolites.

Performance CriteriaPerformance Criteria

Must be able to measure glucose concentrations Must be able to measure glucose concentrations within a biologically relevant range, between within a biologically relevant range, between 0mM and 6mM0mM and 6mM

Must be affordable – less expensive than current Must be affordable – less expensive than current research technology, more expensive than the research technology, more expensive than the disposable strips for diabeticsdisposable strips for diabetics

Needs to work for at least 24 hoursNeeds to work for at least 24 hours Should recalibrate automatically to account for Should recalibrate automatically to account for

electrochemical driftelectrochemical drift

Design Concept Map

Our Design

Our design utilizes a commercially Our design utilizes a commercially produced Pine Instruments electrode that produced Pine Instruments electrode that is much larger.is much larger.This electrode is interfaced with a microfluidic This electrode is interfaced with a microfluidic

pumping device that allows small volumes, on pumping device that allows small volumes, on the microscale, to be studied.the microscale, to be studied.

Design ComponentsDesign Components

ElectrodeElectrodeChannel SystemChannel SystemElectrode HousingElectrode HousingPumping SystemPumping SystemBioreactorBioreactorElectrochemical workstationElectrochemical workstationComputer software – A/D converterComputer software – A/D converter

Design: the ElectrodeDesign: the Electrode

Cellular glucose sensors consist of an Cellular glucose sensors consist of an electrode that utilizes a chemical reaction electrode that utilizes a chemical reaction to determine glucose concentrations.to determine glucose concentrations.

An enzyme film is cast onto the electrode.An enzyme film is cast onto the electrode.The electrode consists of three “contacts”The electrode consists of three “contacts”

Working electrodeWorking electrodeReference electrodeReference electrodeCounter electrodeCounter electrode

Chemical Reaction

This reaction takes place on the electrode.

Platinum Electrode

Nafion

Glucose Oxidase (GOx)

GOx

Glucose

+

O2

O2 (+ H2O)

Gluconolactone + H2O2

e-

Nafion

Potentiostat

An instrument that controls the electrical potential between the working and reference electrodes.Keeps the potential of the working electrode at

a constant level with respect to the reference electrode

Controls the potential across the electrochemical cell by sensing changes in its resistance, and changing the current supplied to the system accordingly

Design: Channel SystemDesign: Channel System

Using a CNC, a PDMS Using a CNC, a PDMS mold was made to mold was made to create uniform create uniform channels.channels.

Solution containing Solution containing glucose is run through glucose is run through these channels, these channels, passing over the passing over the electrode.electrode. Channel

Electrode Shape

Channel Fabrication

CNC mold

PDMS

CNC mold

electrodechannel

Design: Electrode HousingDesign: Electrode Housing

Plexiglass plates are placed on each side Plexiglass plates are placed on each side of the electrode to clamp the PDMS in of the electrode to clamp the PDMS in place, sealing the system from leakage.place, sealing the system from leakage.

Clamping pressure can be manually Clamping pressure can be manually adjusted.adjusted.

Holes are drilled in the plates in order to Holes are drilled in the plates in order to run tubing to the channel.run tubing to the channel.

Electrode Housing

Design: the Pumping SystemDesign: the Pumping System

Tubes are run through holes drilled in the Tubes are run through holes drilled in the plates.plates.

These tubes are attached to the Harvard These tubes are attached to the Harvard Apparatus pumping system.Apparatus pumping system.

The pumping system is controlled using The pumping system is controlled using LabView.LabView.

LabView

Pump controller

Design: BioreactorDesign: Bioreactor

The bioreactor cultures The bioreactor cultures a small amount of a small amount of cells. cells.

The Harvard The Harvard Apparatus pumps Apparatus pumps media and glucose, in media and glucose, in respective tubes, respective tubes, through the bioreactor through the bioreactor to the electrode to the electrode housing.housing.

Design: Electrochemical Design: Electrochemical workstationworkstation

The glucose concentrations are measured The glucose concentrations are measured using a CH Instruments electrochemical using a CH Instruments electrochemical workstation.workstation.

This workstation consists of a Picoamp This workstation consists of a Picoamp Booster and Faraday cage.Booster and Faraday cage.

Design: Computer software

The CH Instruments workstation is an amperometric sensor that measures a current at a fixed applied voltage.

CH Instruments computer software is responsible for converting this analog signal to a digital format.

Design

A/D converter

Bioreactor Pumping system Electrode and housing Electrochemical workstation

Pumping system

Optimization: Electrode and Tubing

We are using profilometry to characterize the electrode

We are also testing to determine the most efficient tubing length

Troubleshooting: Uniformity

In order to have a uniform channel height between experiments, we have designed a PDMS torque wrench.

This uniformity will increase consistency between experiments.

Previous Experiments

Calibration curve in beaker

1mM

2mM

4mM

3mM

5mM

7mM

8mM

9mM

6mM

Previous Experiments

Calibration curve in microfluidic device

Linear Trend

Recent Experiments

Glucose Calibration Curves

y = -2E-07x - 2E-07

R2 = 0.9994

y = -2E-07x - 2E-07

R2 = 0.9988

-1.00E-06

-9.00E-07

-8.00E-07

-7.00E-07

-6.00E-07

-5.00E-07

-4.00E-07

-3.00E-07

-2.00E-07

-1.00E-07

0.00E+00

0 1 2 3 4 5

Glucose Concentration (mM)

Cu

rren

t (A

)

Trial 1

Trial 2

Current Experiments

Cytosensor glucose concentrations

Current Experiments

Cytosensor, 1 mM, and 3 mM glucose concentrations

Expenses

Pine Instruments Electrode: $30Tubing & electrode housing: ~$15Harvard apparatus: $2,000Bioreactor: $20Electrochemistry workstation: $2,000Computer: $1,500Chemicals (i.e. glucose oxidase): $50

Current WorkCurrent Work

Working on new design for new electrodeWorking on new design for new electrodeOptimize channel height and tubing lengthOptimize channel height and tubing lengthRunning manual experiments with Running manual experiments with

cytosensorcytosensorStop-flowStop-flowContinuousContinuous

Future Work

Test LabView pump controllerGet a new mold made for the new

electrodeFind a smaller pumping system

Future Applications

Obtain results for other metabolitesConfigure on chip peristaltic pump Interface with nanobioreactor