Digital Microfluidic Diagnostic Devices: Automating droplet manipulation to process biological samples

Introduction

May 2014 – Group 26

Motivation: Most experiments in biology require multiple sample-processing steps. We aimed to automate these steps on a portable liquid-handling system.

First Approach: We used an electro-wetting method where high electric fields create electrostatic forces that can move droplets of liquid. Second Approach: We developed a novel method where liquid droplets can be moved on a hydrophobic film by motor-controlled rotation of a droplet platform.

Riley Brien (EE), Jared Anderson (EE), Taejoon Kong (EE), Chee Kang Tan (EE) Advisors & Clients: Dr. Santosh Pandey (ECpE), Dr. Rebecca Cademartiri (MSE), Dr. Ludovico Cademartiri (MSE)

Second Approach: Micro-Printed tilting system with GUI control

Design and setup of Micro-Electrode system

Real-time droplet tracking

Superhydrophobic Substrate

Hydrophilic Track Droplet

Figure 6. Hydrophilic channel guides droplet movement Droplet movement is confined to a hydrophilic channel printed on a superhydrophobic film. When the film is tilted by the motorized platform (left), the droplet moves along the channel.

Electrode array fabrication and droplet operations

Operation of Micro-Printed system

Graphical user interface

Develop a droplet manipulation system comprising micro-electrode arrays, electrical circuitry, and a remote imaging interface capable of performing the following operations on liquid droplets:

Dispensing, transport, merging, and splitting droplets.

First Approach: Digital Micro-Electrode system

Project goals

Figure 1. Droplet movement driven by high voltages When a high voltage is applied, electrostatic forces pull the droplet towards the activated electrode. Larger, two-dimensional electrode arrays can manipulate several droplets at once.

Figure 7: Droplet movement sequence (frame-by-frame) A jolting action (cycle of stimulation) is used to move the droplet in small increments.

1 cm

Computer

Micro Electrode Array

Arduino

High Voltage Switching Board

Control Board

High Voltage Amplifier

Feedback

2Vpp Square wave

100Vpp Square wave

Serial Bus

USB

Edge connector

Figure 2: Connection flowchart (left) and assembled electrical circuit (right) The high-voltage control circuit allows activation of individual electrodes remotely through a computer program.

Control board

Power Supply

High-Voltage

Switching Board

High-Voltage

Amplifier

Arduino

Power Supply

Electrode array

b) UV Exposure

c) Develop

d) HCL Etch

e) Strip Photoresist

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Cycle of stimulation

(a) 140 rpm, 5.6 degree

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(c) 140 rpm, 4.8 degree

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(d) 120 rpm, 4.8 degree

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(b) 120 rpm, 5.6 degree 1 cm

Figure 9: Characterizing droplet movement on cross, ladder, and line patterns Droplets on the cross symbol pattern move a consistent distance (0.4±0.016 cm) per cycle of stimulation, compared to the ladder (0.35±0.2 cm) and line symbols (0.08±0.2 cm).

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0.05 sec.

0.10 sec.

a) Spin Coat Photoresist

Figure 8: MATLAB GUI enables control of droplet movement By clicking the GUI buttons, the droplets can be moved across the printed patterns. The speed and angle of rotation can be adjusted, and video and image snapshots can be recorded.

Glass

Mask

ITO

UV Light

Positive Photoresist

Glass ITO

Positive Photoresist

Glass ITO

Positive Photoresist

Glass ITO

Droplet operations

Conclusion

Figure 10: Simultaneous droplet movement (right), Merging and mixing droplets (left)

Figure 3: Electrode array interface and design Our electrode array contains four dispensing reservoirs and a central mixing area. The electrode array interfaces with the control circuit through edge connectors.

Figure 5: Merging two droplets on the electrode array

Figure 4: Fabricating Electrode Arrays We fabricated 20 electrode arrays using photo-lithography techniques.

We have designed two digital microfluidic systems capable of performing basic droplet operations. These systems have the potential to automate biological experiments. Our novel Micro-Printed system in being planned for submission to a journal.

Transport Dispensing Merging Splitting

Serial Bus