DENVER — Forget fancy electronics. Plain old bubbles are enough to direct the flow of liquid through networks of microscopic tubes, called microfluidics. Researchers recently demonstrated that bubbles could act as computer bits by sending liquid this way or that. Now they report constructing a simple type of memory. Such advances may help turn microfluidics into a more practical tool for detecting disease and discovering new drugs.

Microfluidics systems are designed to mix cells, proteins or other molecules with one another, potentially allowing researchers to, say, rapidly detect traces of bacteria or viruses among many small samples of fluid. The trouble is the hydraulics normally used to pump liquids from place to place, says Manu Prakash, a physics graduate student at the Massachusetts Institute of Technology.

"We can design these beautiful microfluidic chips that are small, but everything that controls [the] fluids inside the chip is outside," he says, preventing microfluidics from being complex yet small. "These are not [things] you can wear on your watch." With bubble power, he says, "you can actually put intelligence inside the chip … so all the chip needs is a power source."

In the new system, Prakash and his adviser, Neil Gershenfeld, inject bubbles into specially shaped arrangements of tubes. The presence of a bubble in a tube represents a bit, or a 1, and its absence marks a 0. For some configurations of tubes, a bubble in one tube changes the direction bubbles flow in a nearby tube—in the same way that one current can switch another current on or off in a regular computer [click here for video].

In other arrangements, two bubbles coming from opposite directions are fused together, or a bubble stays on one side of a reservoir until a second bubble enters the other side, displacing it. Besides just controlling the flow, bubbles of one fluid could carry biological samples through a second fluid, Prakash says.

The bubble method can perform all of the basic operations that a computer does, the group reported in a recent Science paper. Prakash presented several new developments during the annual conference of the American Physical Society here, including a simple memory system for storing up to 100 bubbles, built up from the basic elements. He says such a tool could be useful for pharmaceutical chemists who want to mix and match chemical building blocks in many ways to search for new drugs—another application the researchers are working on.

Prakash says that microfluidics designers currently start from scratch with each project, but the bubble technology could offer common building blocks for all microfluidics designs. "That philosophy doesn't really exist right now," he says.