Digital Microfluidic Diagnostic Devices

May 14-26BAdvisor/Clients: Dr. Santosh Pandey, Dr. Rebecca Cademartiri, Dr. Ludovico Cademartiri

Members: Riley Brien (EE), Jared Anderson (EE), Taejoon Kong (EE), Chee Kang Tan (EE)

Website Password may0526

Standard Liquid Handling Steps in Biology

• Example: PCR Purification

– Up to 10 manual pipetting steps

– Different reagents in each step

May 14-26 2www.beckmancoulter.com

Is it possible to automate the different steps using a portable, low cost system to minimize human intervention?

State-of-the-art Liquid Handling Workstation (TECAN F500)

• High-throughput sample-processing

• Large scale

• $40k to >$100k

May 14-26 3

Digital Microfluidic Systems

New automated liquid-handling systems

• Using published methods

– µElectrode system – Electrostatic forces

drive droplet movement on electrode array

• Using novel techniques– µPrinted system – Gravity and mechanical

oscillations drive droplet movement on inkjet-printed surface

May 14-26 4http://www.sciencedirect.com/science/article/pii/S1367593110000955

discrete droplets µL scale

Example of Digital Microfluidics Platform

May 14-26 5

“Two-plate digital microfluidics for dispensing, mixing, and merging droplets”http://www.youtube.com/watch?v=hVAa41qTIqg

1 mm

Overview of Digital Microfluidics

• Controlled droplet movement (actuation) on electrode array

• Electrowetting theory

– 𝑐𝑜𝑠𝜃 = 𝑐𝑜𝑠𝜃0 +𝜀0𝜀𝑟𝑉

2

2𝛾𝑑, 𝜃0-Initial contact angle 𝜃-contact angle,

𝛾-surface tension, 𝑑-dielectric thickness

– Requires high voltage >50V

May 14-26 6http://loolab.chem.ucla.edu/research/proteomics.htmlhttp://gozips.uakron.edu/~aaa80/research.html

Project Goals

• Build a prototype digital microfluidic system

– Implement “Dropbot” hardware

– Fabricate electrode arrays

• Demonstrate key droplet operations:

If possible, design and implement a new droplet-manipulation system

May 14-26 7

Transport

Dispensing

Merging

Splitting

http://cjmems.seas.ucla.edu/?p=fbizqheqoqvthp&paged=2

– Dispensing

– Transport

– Merging

– Mixing

– Splitting

– Parallel control of multiple droplets

– Low voltage (<12V)

– Easy to build

– Low cost (<$100)

– Easy-to-use graphical user interface

Electrical Connectivity of µElectrode System

Modified from Wheeler lab May 14-26 8

PC

ITO Electrodes Array

Arduino

HV Switching Board

Control Board

HV Amplifier

Serial BusFeedback

2Vpp Square wave

100Vpp Square wave

Serial Bus

USB

Edge connector

Hardware Components of our Digital Microfluidics System

May 14-26 9

DMF Control board

Power Supply

High-Voltage Switching Board

High-Voltage Amplifier

Arduino (under control board)

1 in.

Power Supply

ITO glassµElectrode

array

High Voltage Amplifier Design

May 14-26 10

Input: 2 Vpp and required output: 200 VppSignal frequency: 18 kHzPCB Design Software: Eagle CADPCB fabricated by Advanced Circuits

Electrode Array Layout

May 14-26 11

Design and Fabrication of Electrode Array

May 14-26 12

1 cmContact Trace

Electrodes with 50µm spacing

5 mm

Photolithography Mask

Glass

ITOPositive Photoresist

May 14-26 13

1) Spin Coat Photoresist

UV Exposure Develop HCL Etch Strip Photoresist

Glass

Mask

ITO

UV Light

Positive Photoresist

May 14-26 14

Spin Coat Photoresist UV Exposure Develop HCL Etch Strip Photoresist

Glass

ITO

Spin Coat Photoresist UV Exposure Develop HCL Etch Strip Photoresist

Positive Photoresist

ExposedPhotoresist

May 14-26 15

Positive Photoresist

Spin Coat Photoresist UV Exposure Develop HCL Etch Strip Photoresist

Glass

ITOPositive Photoresist

May 14-26 16

Spin Coat Photoresist UV Exposure Develop HCL Etch Strip Photoresist

Glass

ITOPositive Photoresist

May 14-26 17

Applying Dielectric and Hydrophobic Layers

• Parylene C

– High dielectric constant

– Chemical vapor deposition

• Teflon AF 1600

– Hydrophobic layer1 cm

http://pubs.rsc.org/en/content/articlehtml/2008/lc/b803827a

May 14-26 18

Shortedtraces

5mm

µElectrode Droplet Operations

May 14-26 19

µPrinted System Control Platform

May 14-26 20

5 cm

10 cm

• Can droplets be manipulated by tilting?

• First version – too heavy, slow

Revised µPrinted System Control Platform

May 14-26 215 cm

Surface-Tension-Confined Tracks Theory

• Droplet is confined to hydrophilic track

• Superhydrophobic surface provides high contact angle

May 14-26 22

Superhydrophobic Substrate

Hydrophilic TrackDroplet

µPrinted System Substrate Fabrication and Patterning

• Superhydrophobic Coating –Rust-Oleum NeverWet™

• Transparency Sheets

• Inkjet-printer patterned hydrophilic channels

May 14-26 23http://www.epson.comhttp://www.homedepot.com/catalog/productImages

Quick “Pulses” Prevent High Threshold-Angle Problem

May 14-26 24

0° angle 10° angle 30° angle

Rapid, movement at threshold angle

Droplet Movement on Cross, Ladder, and Line Patterns

May 14-26 25

Characterizing Droplet Movement on Cross, Ladder, and Line Patterns

May 14-26 26

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0 5 10 15 20

Dro

ple

t m

ove

me

nt

[cm

]

Cycle of stimulation

Droplet movement per cycle of stimulationCross Ladder Line

0

0.1

0.2

0.3

0.4

0.5

0.6

Cross Ladder Line

Dro

ple

t m

ove

me

nt

[cm

]

Average droplet movement per cycle of stimulation

Cross Ladder Line

µPrinted System GUI Controls

May 14-26 27

µPrinted System Droplet Manipulation

May 14-26 28

Dispensing

Simultaneous loading and mixing

Simultaneous transport

Merging and Mixing

Summary of µElectrode and µPrinted Systems

• µElectrode

– Implemented controller hardware and amplifier

– Fabricated electrode arrays

– Demonstrated droplet operations

• µPrinted

– Developed novel digital microfluidic system

– Demonstrated droplet operations

May 14-26 29

Acknowledgments

• Zach Njus (Graduate student, Dr. Pandey’s group)

• Dr. Wai Leung (Assistant Scientist III, DOE Ames Lab)

• Lee Harker (Electronics Technician II, Coover Hall)

• Dr. Liang Dong (Associate Professor, ECpE)

• Dr. Jaeyoun Kim (Associate Professor, ECpE)

May 14-26 30

Questions?

May 14-26 31

Biological Applications and Advantages

EWOD System RDS System Pipetting robot Manual pipetting

Cost

Speed

Accuracy

Flexibility

Ease of Use

May 14-26 32

Standard methods

http://photos.uc.wisc.edu/photos/3525/view

Digital microfluidics

http://www.ehs.iastate.edu/sites/default/files/uploads/images/pipetting.jpg

ITO Patterning– Problems and Solutions

• Problems

– Shorted traces: many electrodes are actuated at the same time

– Broken traces: can not supply the potential

• Solutions

– Get rid of dust

– Improve mask alignment

May 14-26 33

Hours/feet*12inches/60 minutes

Evolution of DMF Platforms

• 2001 – Duke University and UCLA– First prototypes (1.)

• 2004 – Advanced Liquid Logic– First digital microfluidics company (2.)

• 2011 – Sandia National Lab– First integrated inlet/outlet ports (3.)

• 2012 – University of Toronto – First Open-Source digital microfluidics

system, “Dropbot” (4.)

May 14-26 34http://i1.ytimg.com/vi/9GInRQYzSJg/maxresdefault.jpg

http://www.biw.kuleuven.be/biosyst/mebios/biosensors-home/droplet/image_previewhttp://microfluidics.utoronto.ca/dropbot/media/DropBot_system-labelled.jpg

1. 2.

3.

4.

Project Costs for DMF system

May 14-26 35

• Cost– Control board - $150– Switching board - $300– Amplifier - $800– Indium Tin Oxide (ITO) glass - $1500 (100 pcs.) – Teflon AF 1600 - $1800*– Reagents (photoresist, developer, HCL, Acetone, Methanol,

etc) - Lab supply