Design of a Hand-Held and Battery-Operated Digital Microfluidic Device Using EWOD for Lab-on-a-Chip Applications

Abstract

Microfluidics offer many advantages to Point of Care (POC) devices through lower reagent use and smaller size. Additionally, POC devices offer the unique potential to conduct tests outside of the laboratory. In particular, Electro-wetting on Dielectric (EWOD) microfluidics has been shown to be an effective way to move and mix liquids enabling many PoC devices. However, much of the research surrounding these microfluidic systems are focused on a single aspect of the system capability, such as droplet control or a specific new application at the device level using the EWOD technology. Often in these experiments the supporting systems required for operation are bench top equipment such as function generators, power supplies, and personal computers. Although various aspects of how an EWOD device is capable of moving and mixing droplets have been demonstrated at various levels, a complete self-contained and portable lab-on-a-chip system based on the EWOD technology has not been well demonstrated. For instance, EWOD systems tend to use high voltage alternating current (AC) signals to actuate electrodes, but little consideration is given to circuitry size or power consumption of such components to make the entire system portable. This paper demonstrates the feasibility of integrating all supporting hardware and software to correctly operate an EWOD device in a completely self-contained and battery-powered handheld unit. We present results that demonstrate a complete sample preparation flow for deoxyribonucleic acid (DNA) extraction and isolation. The device was designed to be a field deployable, hand-held platform capable of performing many other sample preparation tasks automatically. Liquids are transported using EWOD and controlled via a programmable microprocessor. The programmable nature of the device allows it to be configured for a variety of tests for different applications. Many considerations were given towards power consumption, size, and system complexity which make it ideal for use in a mobile environment. The results presented in this paper show a promising step forward to the portable capability of microfluidic devices based on the EWOD technology.

Keywords: Electro-wetting on Dielectric (EWOD); Point of Care (POC); digital microfluidics (DMF); lab on chip (LOC); sample preparation.

Figure 1

System block diagram.

Figure 2

Typical DNA isolation protocol.

Figure 3

Nucleic acid extraction chip design.

Figure 4

Completed EWOD chip electrodes.

Figure 5

Position feedback circuit.

Figure 6

Droplet position equivalent circuit. (a) droplet not over the active pad; (b) after droplet has reached the active pad.

Figure 7

PCB layout.

Figure 8

Adjustable high voltage SWPS.

Figure 9

Protocol control flow.

Figure 10

Device implementation (a) Charging/PC connected; (b) Open; (c) Closed.

Figure 11

Magnetic bead EWOD chip layout.

Figure 12

Battery charge waveform.

Figure 13

5 V SMPS power on/off waveforms.

Figure 14

High voltage SMPS power on/off waveforms.

Figure 15

System current consumption for different activation voltage levels.

Figure 16

Position feedback V_sense plots.

Figure 17

Bead method DNA isolation sequences. (a) Move sample to mix area; (b) Move beads buffer to mix area; (c) Mix sample and beads; (d) Move mixture to capture area; (e) Elute beads and move to output.

Figure 18

Plate reader plot.

Figure 19

UV microscope images. (a) sample DNA; (b) waste reservoir; (c) recovered DNA in output reservoir.