An Electrifying Advance

Advances in pathology typically come from professionals in medicine or the life sciences who have dedicated their lives to unraveling the biology of human health and disease. But occasionally, such strides forward come from unusual sources – in this case, the Indian Institute of Technology’s Advanced Technology Development Center, where a group of researchers have developed a way of improving control and flow rate in lab-on-a-chip devices. What makes this so exciting? The new method is easy to implement, improves device performance, and opens up a range of possibilities for future applications of microfluidics (1).

So how does it work? Usually, the tubes in microfluidic chip devices are made of polyvinyl chloride or Teflon. When placed in contact with aqueous electrolytes, these materials acquire a surface charge – which makes fluids behave as if they possess a net counter-charge, opposite in nature and magnitude to that of the tube’s surface. The result? The ability to manipulate these types of devices by applying electrical fields.

Integrated devices that employ peristalsis – surface waves – are a hot topic in microelectromechanical systems (MEMS) research. Peristaltic micropumps can achieve a high surface oscillation frequency within a compact structure, but they aren’t very flexible in terms of characteristics. For example, you have only a small range of actuation frequencies and surface wave amplitudes to choose from. By assisting or resisting the direction of peristaltic transport, auxiliary electric fields address precisely this drawback. “It has been shown theoretically that one may achieve unprecedented control over the flow rates obtained by otherwise rigid devices,” says Suman Chakraborty, senior author of the new research, “from completely reversed flow rates to twice the forward flow rate.”

Electro-osmosis isn’t an instant fix, though; there are still obstacles to be overcome. “The main challenges in implementing such a device lie in the microfabrication,” says Chakraborty. “The concept of sputtering – depositing thin films of electrodes onto a surface – and the associated fabrication have been demonstrated by several researchers in the MEMS community. Obtaining the necessary actuators seems to be the restricting factor.” There are also considerations with regard to utility. Electro-osmosis relies on transporting an ionic solution (one that can carry a current). To transport any other type of solution, Chakraborty explains, you’d need to set up a two-fluid system in which you use a fine-tuned ionic solution to control transport of the non-ionic one.

The next step for Chakraborty and his colleagues is to create initial prototypes of such devices using existing microfabrication facilities. “This could make way for integrated devices that require the slowing down or enhancement of flow rates without affecting any moving parts – thus maintaining high reliability.” Although there’s still plenty of research to be done into how charged particles move in electro-osmotically modified environments, the ultimate outcome may be tiny, finely tuned lab-on-a-chip devices with a wider range of applications than ever.