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Holographic technique could boost lab-on-a-chip

Posted: 04 Dec 2008 ?? ?Print Version ?Bookmark and Share

Keywords:electrokinetic pattern? holographic technique? lab-on-a-chip?

Purdue University researchers have developed an electrokinetic patterning technique that utilizes laser and holograms to quickly position numerous tiny particles.

The technique could be used to analyze biological samples or create devices using nano-assembly as a potential alternative to existing patterning techniques.

The method also could advance future "lab-on-a-chip" technology, in which chips are used to analyze biological samples. Researchers are trying to develop such "high throughput" chips to quickly detect numerous particles or molecules using the smallest sample possible.

The technique could also allow researchers to design sensor technologies that move particles to specific regions on a chip for detection and analysis.

"If you want to pattern individual particles on a massive scale using electrokinetic methods as precisely as we are doing it, it could take hours to days, where we are doing it in seconds," claimed Purdue researcher Stuart Williams. "We can pattern light, we can pattern particles, we can pattern the vortex."

The experimental device consists of two parallel electrodes made of indium tin oxide spaced 50 micrometers apart. A liquid sample containing fluorescent beads was injected between the two electrodes, then a laser in the near IR range of the spectrum was shined through one of the transparent electrodes. Finally, a small electrical voltage was applied between the two electrodes.

The electrode is biased with an ac signal and illuminated with 1,064nm optical wavelengths. Particle groups are assembled at less than 100kHz rates.

"We send holograms of various patterns through this and, because they are holograms, we can create different shapes, such as straight lines or 'L' patterns," said doctoral student Aloke KumarKumar, part of a research team at the Birck Nanotechnology Center in Purdue's Discovery Park.

The particles in the liquid sample automatically move to the location of light and assume the shape of a hologram. The method could be used to move particles and molecules to specific locations as well as to create tiny electronic or mechanical features.

The researchers claim their technique overcomes limitations inherent in two existing methods for manipulating particles at the nanometer level. One technique, called optical trapping, uses a highly focused light beam to capture and precisely position particles. However, the technique is only able to move a small number of particles at once.

The other technique, known as dielectrophoresis, uses electric fields generated from metallic circuits to move many particles at once. Those circuit patterns, however, cannot be changed once created.

The new method is able to simultaneously position numerous particles and be quickly changed by altering the shape of the hologram or the position of the light.

- Nicolas Mokhoff
EE Times

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