Researchers at Purdue University have found a new method in particle manipulation. This new tool could be applied in areas ranging from food and water contamination testing to crime scene forensics.

The results, published in the journal “Langmui”r on June 1, details how scientists were able to position droplets to achieve a more effective sensor. Regularly, particles are detected after they fall randomly onto a sensor's surface. Newer methods are able to position droplets or the particles within using light fields or electric fields. However, the "hybrid optoelectric" method employs both light and electric fields to position not only the droplets, but also the particles. This makes it potentially practical for sensors and industrial processes, said Aloke Kumar, mechanical engineering doctoral student.

Electrodes of indium tin oxide are necessary for the new technology. While indium tin oxide, a clear and conductive material, is normally used for touch-screen displays in consumer electronics, researchers positioned liquid drops on the electrodes. By heating up both the electrodes and droplets via infrared laser, the electric fields of the electrodes cause a "microfluidic vortex" of heated liquid. This circulating liquid tornado allows researchers to position the particles. Wherever the infrared laser is moved, and therefore shined, the particles accumulate there. 

"Sensors are one of the immediate applications of this technology," explained Kumar, "we should be able to improve the efficiency of sensors at least ten times."

Because the technology is able to manipulate a wide range of droplets and particles sizes -- going all the way from microliter drops to particles a few nanometers long -- the hybrid technique can be applied universally according to Steven Wereley, a professor of mechanical engineering who worked with Kumar. The hybrid sensor could be used to quickly analyze blood and other bodily fluids (applicable in a range of situations); finding coronary artery disease, tumors, and other inherited diseases; as well as determining viruses and fungi that prove difficult to culture in traditional laboratory methods. Food and water testing are also a possibility, like detecting E. coli or salmonella. Moreover, with criminal investigators struggling over small blood samples, this could make DNA testing much easier. 

The hybrid method also shows promise for "lab-on-a-chip" technology. This uses electronic chips to analyze biological samples for a variety of applications, from medical to environmental.

Purdue has applied for a U.S. patent application on the design. The findings were detailed in a research paper, written by Kumar, Wereley, and Han-Sheng Chuang, a former Purdue doctoral student and current postdoctoral researcher at the University of Pennsylvania.