The team, which used a newly developed laser-processing technique to create the miniature detector, was supported by the National Science Foundation and led by a Purdue University engineer who conducted the work while he was at the University of California, Berkeley.

"Now we have a way of putting all of the critical components on one wafer," said Timothy D. Sands, the Basil S. Turner Professor of Engineering in the School of Materials Engineering and the School of Electrical and Computer Engineering at Purdue. "It's much the same in concept as going from separate transistors to an integrated circuit that includes many transistors on a single chip."

Findings about the miniature detector are detailed in a paper that has been posted online and that will appear March 1 in Sensors and Actuators A: Physical, an international journal published in Amsterdam by Elsevier B.V.

The paper was written by Sands and the following researchers from UC-Berkeley: J. Alex Chediak and Zhongsheng Luo, graduate students in materials science and engineering; Jeonggi Seo, a graduate student in applied science and technology; Nathan Cheung, a professor of electrical engineering and computer science; and Luke P. Lee, a professor of bioengineering.

The traditional fluorescence detection system works by attaching a fluorescent dye to specific molecules in a substance and then shining a laser onto the substance. The laser light is absorbed by the dyed molecules, causing them to emit a certain color, which is picked up by a sensor. The detection work normally is done using bulky, stationary equipment in a laboratory.

The new device, however, fits on a centimeter-wide chip, promising the development of miniature detectors that can be used in the field. Such portable instruments would be useful for a wide range of applications, from biologists doing basic research to farmers testing crops for toxins.

To create the chips, the team used a technique invented by Sands, Cheung and former graduate student William Wong, now a researcher at the Palo Alto Research Center in Palo Alto, Calif. This technique, known as "laser liftoff," uses a powerful laser to selectively separate and transfer thin-film components from one substrate to another to build up the successive layers of a "system-on-a-chip."

"We use lasers to manipulate materials, either to grow them or to process them," said Sands, who specializes in heterogeneous integration, or making devices by combining entirely different materials in new ways. "We can transfer films of materials from one substrate to another, and then use this laser-based assembly process to build up complex systems made of materials from different classes that are not normally compatible."

Fluorescence detection is commonly used in industry and science.

"It's the standard technique," Sands said. "The idea is that you tag a specific molecule or cell with a dye molecule that will emit light when it's excited. Then you illuminate your subject that's been tagged with the dye molecule, causing it to emit light at a longer wavelength."

The color of the laser is chosen to efficiently "excite" a specific dye. Shining a blue laser

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