NO time like the present
Technology catches up — 30 years later — to Rice scientists’ idea for trace-gas sensor

BY MIKE WILLIAMS
Rice News staff

Persistence pays. Ask Robert Curl.

Nearly 30 years ago, long before he won the Nobel Prize for Chemistry as co-discoverer of the carbon-60 “buckyball,” the Rice University professor and his colleague Frank Tittel came up with a way to measure nitric oxide (NO) and other atmospheric chemicals using lasers. It’s taken this long for the technology that makes it possible to catch up.

Their recent paper details the workings of a nitric oxide sensor that has wide applications in environmental and health-related monitoring and has already proven its worth at the 2008 Olympics.

	ROBERT CURL
	FRANK TITTEL
	GERARD WYSOCKI

The sensor is described in a paper published this month in the Proceedings of the National Academy of Sciences by Curl, University Professor Emeritus and the Kenneth S. Pitzer-Schlumberger Professor Emeritus of Natural Sciences; Tittel, Rice’s J.S. Abercrombie Professor in Electrical and Computer Engineering; Gerard Wysocki, a former Rice faculty fellow and now an assistant professor of electrical engineering at Princeton University; Jones College senior James Doty; and visiting graduate student Rafal Lewicki.

The paper was published nearly a year to the day after the opening ceremony of the Beijing Olympics. Tittel, Lewicki and Wysocki went to China as part of a research team that spent two months detecting and monitoring the atmosphere for nitric oxide, a free radical molecule that is also a pollutant produced by cars and power plants. It contributes to smog, acid rain and the depletion of Earth’s ozone layer.

In Beijing, where the Chinese government had shut down factories and blocked highways in advance of the games to cut pollution, the concern was for the health of athletes, particularly those in such endurance events as cycling and the marathon. Their successful effort to clear the air was detailed in a report released by Cornell University this week.

Nitric oxide is also produced by the human body, which uses it as a messenger between cells and to help regulate the cardiovascular system. But it’s toxic in large doses, said Curl, who noted the device has potential for gleaning information about a patient’s condition just by testing his or her breath, as excess NO can be a marker for chronic obstructive pulmonary disease and inflammation. “It’s remarkable we have that kind of sensitivity,” he said.

Curl, who shared the 1996 Nobel Prize with the late Richard Smalley of Rice and Harold Kroto of Florida State University, specializes in infrared laser spectroscopy and the kinetics of free radicals, molecules that easily combine with others to form new compounds. His 1980 paper with Tittel in the Journal of Chemical Physics laid the groundwork for the device that went to the 2008 Olympics. “I had a lot of fun with this particular paper because we revisited an old thing and were seeing new aspects,” he said.

The quantum cascade laser (QCL), which Curl said is the size of a piece of pencil lead, makes the detector possible. The lasers invented in 1994 and commercialized in 2002 emit light in the mid- to far-infrared range. Their high power, tuning range, low interference and ability to operate at room temperature made them perfect for the kind of spectroscopy that could identify trace gases, which can be distinguished by the wavelength of light they absorb. The new device can pick out specific molecules in a volume of gas at a concentration of parts per billion, Curl said.

Having a portable device that can continuously measure NO to such a high degree of sensitivity is a significant breakthrough, said Tittel, who noted that sensors previously used for such analysis were large and expensive and required samples to be analyzed in a time-consuming laboratory process.

An artist’s rendering shows the components of the nitric oxide detector a Rice and Princeton team brought to the 2008 Olympics. Details of the device were revealed in a new paper this month, but its origins go back nearly three decades. Please click on the image to view a larger version.

Tittel said Curl was the driving force behind the 1980 paper, but the idea was dormant until the inventor of the QCL, Federico Capasso (then of Bell Labs and now at Harvard) and his team, in particular Claire Gmachl, now at Princeton University, “identified Bob and my group as a good beta site for his new technology.

“He provided us with some early quantum cascade lasers 11 years ago, and within a year, I realized it gave us an opportunity for the nitric-oxide-sensor work to be resurrected,” Tittel said. “It took the quantum cascade laser 29 years to make this measurement reliable and robust. It’s very enjoyable that it happened on my watch.”

Despite the sensor’s long gestation, Tittel, Wysocki and their teams worked day and night for three months to prepare the instrument for the Beijing Olympics. At Princeton, Wysocki took what started on a tabletop at Rice and developed a transportable instrument, though it still weighed 500 pounds.

Now he’s working on the next generation. “We’re improving the technology in general,” Wysocki said. “We already can increase the sensitivity by an order of magnitude, and that allows the size of the instrument to be reduced. At the moment, the same technology would almost fit in a shoebox.” Wysocki has proposed the further development of dedicated NO sensors to the National Institutes of Health.

Curl has his eye on building a new version of the sensor to study nitrogen dioxide, another air pollutant and one of a number of target molecules the technology may address. “It’s in a different wavelength region and requires a different laser,” he said. “So we have to get our hands on such a laser.”

The research was supported by the National Science Foundation through Princeton’s Mid-InfraRed Technologies for Health and the Environment Engineering Research Center, the Department of Energy through a subaward from Aerodyne Research Inc. and the Robert Welch Foundation.