Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Engineers create chip-size version of widely used detector

13.02.2004


Researchers have created a portable, chip-size version of a detection system that is commonly used by industry and law enforcement to identify everything from agricultural toxins to DNA.



The miniature detector could move certain types of testing from the lab into the field, saving time and money while increasing security.

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 on a certain dye, for example, results in the emission of green light. A green laser might be chosen to excite a dye that emits red light.

DNA is tagged with a specific dye and then a fluid containing the tagged DNA is passed under a laser beam. The light-emission data are collected and analyzed, revealing information about the DNA.

"You also have to have some way of filtering the light," Sands said. "If, for example, you are using a laser that emits blue light, you can’t allow the blue light to go into your photo-detector because it will wash out the signal from the green light the excited molecules emit.

"You have to filter out the blue light and just pick up the green."

The research team had to create a tiny filter that could fit on a chip.

The "light-emitting diode," or LED, that emits blue light is a thin layer of gallium nitride that’s formed on top of a sapphire crystal. When electricity is passed through the LED, it produces a blue light.

With laser liftoff, the researchers use a device called an excimer laser to shine fast pulses of ultraviolet light onto the sapphire. Each pulse lasts only about 25 nanoseconds, or 25 billionths of a second. The concentrated energy removes the sapphire substrate on which the blue LED is formed, leaving behind only the thin layer. The LED film is transferred by the laser onto a filtering layer of cadmium sulfide, which screens out blue light. The layered diode and filter are then added to a photo detector on a single chip.

The thin-film LED is five micrometers – or millionths of a meter, thick – which is about one-twentieth as thick as a human hair, and is produced for less than $1, replacing the bulky and expensive laser in bench-top fluorescence detection instruments, Sands said.

"Something new that we recently reported was to put two colors, a blue and green LED, on one chip," he said.

Adding the green LED also meant adding another filter. Illuminating dyed molecules with a green LED causes the dye molecules to emit a reddish light. The second filter keeps green light from getting into the photo-detector so that it only detects the reddish light emitted by the excited dyed molecules.

At least two colors are considered critical for the analysis of biological and chemical materials.

"If you wanted to do biochemical detection of anthrax or some other substance, you almost always have to have two colors and your sample is tagged with two dyes," Sands said. "One serves as a control – to precisely calibrate the measurement – and the other color is for actually detecting the molecule you are after.

"We are now arguing that we can combine more than two colors, as well as arrays of LED-filter pairs. We could also build a spectrometer on a chip using an array of ultraviolet LEDs and a series of thin-film filters that absorb different colors."

The team is in the process of comparing the performance of the integrated microchip to bench-top instruments.

"Even if the performance never exceeds that of laser-based bench-top systems, the small size of the fluorescence detection microchip suggests a future as a portable, hand-held device for chemical detection and bioassay applications in remote locations," Sands said.

Writer: Emil Venere, (765) 494-4709, venere@purdue.edu
Sources: Timothy D. Sands, (765) 496-6105, tsands@purdue.edu
J. Alex Chediak, (510) 643-5304, chediak@uclink.berkeley.edu
Zhongsheng Luo, (510) 643-7036, zsluo@berkeley.edu

Sarah Yang, public information representative, UC-Berkeley, (510) 643-7741, scy@pa.urel.berkeley.edu

Note to Journalists: The research paper is available from Emil Venere, (765) 494-4709, venere@purdue.edu. It also can be found online.

Emil Venere | Purdue News
Further information:
http://news.uns.purdue.edu/html4ever/2004/040212.Sands.detector.html
http://www.sciencedirect.com/science/journal/09244247

More articles from Process Engineering:

nachricht Additive manufacturing, from macro to nano
11.04.2017 | Laser Zentrum Hannover e.V.

nachricht Dresdner scientists print tomorrow’s world
08.02.2017 | Fraunhofer-Institut für Werkstoff- und Strahltechnik IWS

All articles from Process Engineering >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

Im Focus: Quantum-physical Model System

Computer-assisted methods aid Heidelberg physicists in reproducing experiment with ultracold atoms

Two researchers at Heidelberg University have developed a model system that enables a better understanding of the processes in a quantum-physical experiment...

Im Focus: Glacier bacteria’s contribution to carbon cycling

Glaciers might seem rather inhospitable environments. However, they are home to a diverse and vibrant microbial community. It’s becoming increasingly clear that they play a bigger role in the carbon cycle than previously thought.

A new study, now published in the journal Nature Geoscience, shows how microbial communities in melting glaciers contribute to the Earth’s carbon cycle, a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

New quantum liquid crystals may play role in future of computers

21.04.2017 | Physics and Astronomy

A promising target for kidney fibrosis

21.04.2017 | Health and Medicine

Light rays from a supernova bent by the curvature of space-time around a galaxy

21.04.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>