Lasers Key to Handheld Gas and Liquid Sensors

August 4, 2005
Lasers Key to Handheld Gas and Liquid Sensors

Terrorists have just laced the water supply of a major metropolis with a chemical so lethal that only small amounts are needed to kill thousands of people. But the chemical never reaches its targets. Tiny liquid phase sensors at strategic points in the city’s water mains detect the chemical as it passes and tell a computer to close down the affected pipes.

Image: Boris Mizaikoff displays a prototype of the gas phase sensor, while graduate student Christy Charlton holds the liquid phase prototype.

Current technology is too cumbersome for this kind of rapid detection and response. But new advances in liquid and gas phase chemical sensing being made at the Georgia Institute of Technology may lead to the development of palm-sized sensing tools that can provide the instant detection needed to stop such an attack.

Using small quantum cascade lasers, researchers at Tech, along with colleagues from Tel-Aviv University and OmniGuide Communications, have built and demonstrated a prototype handheld gas phase chemical sensing device and a liquid phase sensing device. The details appear in the July 15, 2005 issue of Analytical Chemistry and the May 9, 2005 issue of Applied Physics Letters.

The quantum cascade laser is the key to scaling down midinfrared chemical sensing tools to fit in the palm of the hand, said Boris Mizaikoff, associate professor in the School of Chemistry and Biochemistry at Georgia Tech.

"This diode laser light source emits midinfrared frequencies, operates at room temperature and is small – roughly the same size as the laser you use in a laser pointer or CD player,” said Mizaikoff.

Almost every organic molecule has a very distinctive absorption pattern in the midinfrared range (roughly between three and 20 microns) Illuminating molecules with a laser tuned to its fingerprint frequency will cause the molecules to vibrate as they absorb radiation at that frequency.

Detecting a chemical is as simple as illuminating a small volume of gas or liquid with a laser. If the laser is tuned to a characteristic absorption frequency of benzene, for example, and benzene is present, the molecules will vibrate and absorb an amount of radiation at its characteristic absorption frequency indicating its concentration.

"The quantum cascade lasers can be designed by bandstructure engineering to emit almost anywhere in the midinfrared band,” said Mizaikoff. “So, if the molecule you want to detect has an absorption at 11 microns, you design a laser that emits precisely at that frequency. With the concept of the quantum cascade laser, that’s possible for the first time.”

For the gas sensing modules, Mizaikoff and his student Christy Charlton use a photonic band gap hollow waveguide (developed by OmniGuide),essentially a hollow, flexible tube, to both contain very small amounts of the air being sampled and assist in sensing. The waveguide can be built to propagate only one wavelength of light very well. So when the laser illuminates the gas molecules inside the waveguide, the waveguide will propagate only the selected fingerprint frequency for detecting a specific molecule.

"In our paper, we've shown that if we take only one meter of photonic band gap hollow waveguide with an inner diameter of 700 microns coupled to a frequency-matched quantum cascade laser, we've been able to detect levels down to 30 parts-per-billion (ppb) of ethyl chloride,” said Mizaikoff. “In our opinion, it’s among the most sensitive measurement that’s been demonstrated in gas phase sensing in a hollow wave guide to date.”

Gas sensing done this way requires a sample of only one milliliter of gas, compared to few hundreds of milliliters for other techniques using regular multi-pass gas cells, he added.

One of the most promising applications for this technology is breath diagnostics, said Mizaikoff.

"A lot of diseases, like asthmatic conditions or acute lung injuries, have specific biomarkers that are contained in breath,” he said. “The problem is that you have a dramatic increase of these markers, but still at very low concentration levels, so you need extremely sensitive and reliable tools to detect these changes. We believe this is one way to develop a very compact sensing device, which could provide the sensitivities needed for breath diagnostics.”

Since the lasers are so small, devices could be made to sense multiple chemicals by simply adding more lasers.

For the liquid phase device, researchers use a planar silver halide waveguide, developed at Tel-Aviv University, to transmit the radiation. As with the gas devices, the quantum cascade lasers vastly increase the sensitivity of liquid phase chemical detection at the surface of this waveguide.

"By making the waveguide thinner and coupling the laser into that, we’re actually increasing the amount of energy transported in the so-called evanescent field, which means the sensitivity goes up,” said Mizaikoff.

Currently, there are only few techniques available that can provide an instant response at trace-levels in water monitoring. Usually, gas or liquid chromatography, which require collecting samples, is needed to detect such fine amounts.

"This might be the road to sensors that can continuously measure at ppb levels, with molecular selectivity, and instantaneously,” said Mizaikoff. “We believe this technology will be the inroad to single digit ppb water quality measurement.”

Link: Applied Sensors Laboratory

Source: Georgia Institute of Technology

Explore further: Nanoscale diamond 'racetrack' becomes breakthrough Raman laser

Related Stories

SETI reborn—the new search for intelligent life

September 10, 2015

A new influx of money has saved the Search for Extraterrestrial Intelligence (SETI) from collapse, but what does the future hold for our quest to discover intelligent life in the Universe?

'Zeno effect' verified—atoms won't move while you watch

October 23, 2015

One of the oddest predictions of quantum theory – that a system can't change while you're watching it – has been confirmed in an experiment by Cornell physicists. Their work opens the door to a fundamentally new method ...

Technology tackles space junk

October 22, 2015

Orbital debris can cause problems for space travel and satellites, so scientists have banded together to come up with innovative solutions, from laser cannons to proactive removal.

Could we terraform the sun?

September 11, 2015

In the list of crazy hypothetical ideas, terraforming the sun has to be one of the top 10. So just how would someone go about doing terraforming our sun, a star, if they wanted to try?

Recommended for you

New gene map reveals cancer's Achilles heel

November 25, 2015

Scientists have mapped out the genes that keep our cells alive, creating a long-awaited foothold for understanding how our genome works and which genes are crucial in disease like cancer.

CERN collides heavy nuclei at new record high energy

November 25, 2015

The world's most powerful accelerator, the 27 km long Large Hadron Collider (LHC) operating at CERN in Geneva established collisions between lead nuclei, this morning, at the highest energies ever. The LHC has been colliding ...

A blue, neptune-size exoplanet around a red dwarf star

November 25, 2015

A team of astronomers have used the LCOGT network to detect light scattered by tiny particles (called Rayleigh scattering), through the atmosphere of a Neptune-size transiting exoplanet. This suggests a blue sky on this world ...

Study suggests fish can experience 'emotional fever'

November 25, 2015

(—A small team of researchers from the U.K. and Spain has found via lab study that at least one type of fish is capable of experiencing 'emotional fever,' which suggests it may qualify as a sentient being. In their ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.