New Tool Analyzes Biological Samples

The technique, called rapid electrokinetic patterning, is a potential alternative to existing technologies because the patterns can be more quickly and easily changed, said mechanical engineering doctoral student Stuart J. Williams of Purdue University.

The experimental device consists of two parallel electrodes made of indium tin oxide, a transparent and electrically conductive material. The parallel plates were spaced 50 micrometers, or millionths of a meter, apart, equivalent to two-thousandths of an inch or about the diameter of a human hair. A liquid sample containing fluorescent beads was injected between the two electrodes, a laser in the near infrared range of the spectrum was shined through one of the transparent electrodes and a small electrical voltage was applied between the two electrodes.

"We send holograms of various patterns through this and, because they are holograms, we can create different shapes," doctoral student Aloke Kumar explained.

The particles in the liquid sample automatically move to the location of the light and assume the shape of the hologram, meaning the method could be used to not only move particles and molecules to specific locations but also to create tiny electronic or mechanical features.

The light heats up the liquid sample slightly, changing its density and electrical properties. The electric field applied to the plates acts on these altered properties, causing the heated sample to circulate, much like heated air causes convection currents in the atmosphere, producing a donut-shaped "microfluidic vortex" of circulating liquid between the two plates.

This vortex enables the researchers to position the particles in the circulating liquid by moving the laser light.

"If you have particles of two different types, you can sort one group out and keep the other behind. It's a versatile tool," Williams said.

Separating particles is important for analyzing medical and environmental samples. The system could allow researchers to design sensor technologies that move particles to specific regions on an electronic chip for detection or analysis.; Source: University of Purdue