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

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

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.

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

***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.

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

Design Concept Map

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.

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

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

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 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

Channel Fabrication CNC mold PDMS CNC mold electrode channel

***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.

Electrode Housing

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.

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.

Design: Electrochemical workstation The glucose concentrations are measured using a CH Instruments electrochemical workstation. This workstation consists of a Picoamp 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 Bioreactor Pumping system Electrode and housing Electrochemical workstation A/D converter

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

Previous Experiments Calibration curve in microfluidic device Linear Trend

Recent Experiments

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

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++

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

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