Project Background


This design project is to be completed as a mandatory component of the Nanotechnology Engineering curriculum, but is also an important component of various projects under development in the SIMS lab. The overall objective is to design and fabricate a completely on-chip microfluidic pump based on alternating current electroosmotic phenomenon (ACEO). A major focus of the design is integration of the pump into various lab-on-a-chip applications, such as PCR chips, portable biosensors, and remote devices.

Project Objectives

The primary objectives of the project are to:

1) Develop a microfluidic device capable of moving fluids of varying composition at required flow rates under low operating voltages, by employing ACEO pumping technology (see below)

2) Optimize micropump design to minimize power consumption and joule heating

3) Develop real time pump controls through the use of integrated circuitry for controlling the flow speed, and integrated sensors for determining the flow speed

ACEO Technology Overview

Typical "on-chip" pumping technologies require external equipment to operate and control the fluid flow, restricting their applicability to lab environments. For example, pneumatic pumps require compressed gas sources, and DC electro-osmotic pumps require high voltage power supplies. AC electroosmotic pumps, however, have the potential to be contained and controlled completely on-chip. The basic operational principle is given in the illustration to the right. Arrays of asymmetric electrode pairs are fabricated inside microchannels, and an AC voltage signal is applied. This creates an electrokinetic force that will produce net fluid flow through the microchannels.


 
Advantages of an AC Micropump
There are a wide range of micropump technologies that have the potential for pumping small amounts of fluid on-chip. We have chosen AC electroosmotics as the platform for developing an integrated pump based on the following important advantages:
  • The system requires very low voltages (~5V) and power consumption (~10mW) to operate, giving it the ability to be battery powered and fully self-contained on a chip
  • Since there are no moving parts involved in the system, it is a robust design with reduced chances of failure
  • The relatively straight-forward and simple fabrication requirements make it easily compatible with existing microfabrication technology
  • With such a small on-chip footprint, it enables easy integration with existing microfluidic systems
As part of our preliminary work on the project, we have developed a complex model of the working pump using FEM Multiphysics simulation software. These simulations are an important tool that allow investigation and optimization of the numerous parameters governing the fluid flow; an example is shown below.

 Flow lines from FEM Simulation

By performing a sensitivity analysis on the applied peak voltage, estimations on the velocities achievable with this pump design can be made. Shown below is an example of the fluid velocity profile achieved at various applied voltages.

 Velocity Profile vs Applied Voltage


AC Micropump Applications and Market

The market for microfluidic devices has seen rapid growth in recent years. In 2005 it was worth an estimated $2.9 billion, growing to $3.2 billion in 2006, and projected to be $6.2 billion by 2011 [1]. Microfluidic devices have applications in countless fields, such as lab-on-a-chip devices for drug discovery and delivery, and portable sensors for monitoring the presence of specific molecules.

The micropump being developed in this project will be an important enabling technology for many areas of microfluidics. In particular, portable sensors would benefit greatly from a low power, cheap, completely on-chip micropump. Remote sensing of water quality, for detection of harmful agents and acts of bioterrorism, could be realized. Also, cheap and portable sensors are greatly desired for researchers working outside of their labs, as it is often costly, time consuming, and difficult to transport samples from the field back to the lab. 

Microfluidic systems are used often in laboratories for many purposes, such as studying many chemical reactions in parallel, or examining the behavior of cells and other biological molecules in various environments.  In any case, these setups require expensive microfluidic pumps that are controlled with various sensors, valves, and tubing, all of which are located externally. This can make such setups complicated and expensive. Being able to integrate the pump and flow controls within the microfluidic chip would allow an all in one microfluidics package to be offered to researchers. The technology being developed in this project is an important step in realizing the all in one microfluidics system.