1. Microfluidic Glucose Sensor Senior Design Group 4
Kristen Jevsevar
Jason McGill
Sean Mercado
Rebecca Tarrant

2. Problem Statement Primary Objective
Quantify glucose and other metabolite consumption/production on a scale of microliters
Design a glucose electrode interface that will measure micro-scale concentrations while maintaining affordability
Once proven, extend this to lactate, oxygen, and pH

3. Applications
Inexpensive glucose monitors are regularly used by diabetics.
Biological researchers may use similar techniques to study cellular metabolism and toxicology.
Our device will not be used in diabetic diagnostics.

4. Applications
Currently, researchers measure extracellular metabolites, such as glucose, on the scale of milliliters.
Microfluidics works on micro and nanoliters.
Smaller volumes yield faster and more accurate results.
Less expensive and can be done with massive parallelization
Near real time 4

5. ***Similar Systems
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.
Specially designed electrodes already exist that are able to measure glucose concentrations.
This technology can be extended to multiple metabolites.
They are expensive to make and often measure more accurately than necessary for some experiments.
Add more in depth info… point out the difference between clinical applications and personal disposable use.

6. Performance Criteria
Must be able to measure glucose concentrations within a biologically relevant range, between 0mM and 6mM
Must be affordable
Needs to work for at least 24 hours
Should recalibrate automatically to account for electrochemical drift

7. Design Concept Map

8. Our Design
Our design utilizes a commercially produced electrode that is much larger.
This electrode is interfaced with a microfluidic pumping device that allows small volumes, on the microscale, to be studied.

9. Design Components Electrode Channel System Electrode Housing
Pumping System
Bioreactor
Electrochemical workstation
Computer software – A/D converter

10. Design: the Electrode
Cellular glucose sensors consist of an electrode that utilizes a chemical reaction to determine glucose concentrations.
An enzyme film is cast onto the electrode.
The electrode consists of three “contacts”
Working electrode
Reference electrode
Counter electrode

11. Chemical Reaction This reaction takes place on the electrode.
Platinum Electrode
Nafion
Glucose Oxidase (GOx)
GOx
Glucose + O2
O2 (+ H2O)
Gluconolactone + H2O2 e-
Nafion

12. 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

13. Design: Channel System
Using a CNC, a PDMS mold was made to create uniform channels.
Solution containing glucose is run through these channels, passing over the electrode.
Channel
Electrode Shape

14. Channel Fabrication
CNC mold
PDMS
CNC mold
electrode
channel

15. ***Design: Electrode Housing
Plexiglass plates are placed on each side of the electrode to clamp the PDMS in place, sealing the system from leakage.
Clamping pressure can be manually adjusted.
Holes are drilled in the plates in order to run tubing to the channel.

16. Electrode Housing

17. Design: the Pumping System
Tubes are run through holes drilled in the plates.
These tubes are attached to the Harvard Apparatus pumping system.
The pumping system is controlled using LabView.

18. Design: Bioreactor The bioreactor cultures a small amount of cells.
The Harvard Apparatus pumps media and glucose, in respective tubes, through the bioreactor to the electrode housing.

19. Design: Electrochemical workstation
The glucose concentrations are measured using a CH Instruments electrochemical workstation.
This workstation consists of a Picoamp Booster and Faraday cage.

20. 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.

21. ***Design Bioreactor Pumping system Electrode and housing
Electrochemical workstation
A/D converter

22. Previous Experiments Calibration curve in beaker 1mM 2mM 3mM 4mM 5mM

23. Previous Experiments Calibration curve in microfluidic device
Linear Trend

24. Recent Experiments

25. Expenses Electrode: $30 Tubing & electrode housing: ~$15
Harvard apparatus: $2,000
Bioreactor: $20
Electrochemistry workstation: $2,000
Computer: $1,500
Chemicals (i.e. glucose oxidase): $50
Make slide current and future implementation

26. Current Work Ordering Y-joint and tubing Running manual experiments
Stop-flow
Continuous
Taking tent pictures of design components
Deciding whether to use LabView or C++

27. Future Work
Run experiments to create a standard curve of concentrations
Re-do summer experiments with new mold
Get a new mold made for the new electrode
Find a smaller pumping system

28. Future Applications Obtain results for other metabolites
Configure on chip peristaltic pump
Interface with nanobioreactor