James Demas likes his work because "it's pretty."
But as a chemistry professor, he confesses that he researches chemicals that give off light also because the research has practical applications.
Demas and his group in the Chemistry Department study luminescence, a process where chemicals absorb energy from their environment and release that energy at some later time in the form of light. This is how those little glow-in-the-dark stars on dorm ceilings glow. Depending on the chemicals and the situation, luminescent light shines in many colors and can be released within microseconds or hours of exciting the chemicals.
Demas invented a luminescent system that allows scientists to precisely determine oxygen levels in a solution, which is important in many aspects of biological research and has surprising applications in aerospace engineering. His newest project is a sensor that unobtrusively - and non-toxically - measures pH levels in solution, with important applications in chemistry and medicine.
Despite his intimidating "analytical chemist" title and impressive list of accomplishments, Demas is colorful and energetic. He wears a string bolo tie straight out of an old Western movie and writes movie reviews in his spare time. He often disperses his reviews via e-mail to the Chemistry Department and Brown College lists.
His office - a tiny cube in the depths of the Chemistry Building - looks even smaller from the heaps of paper covering every inch of desk space. He gestures to a table in the hallway outside his office where he wants to talk about his research, but doesn't actually sit down for the first half-hour of the interview - he keeps jumping up to retrieve visual aids.
He is eager to explain his work, but won't begin before showing off the magic that occurs in a dark corner of his lab.
He turns off all the lights in the laboratory except for a single black light. He picks up several bottles of solids and solutions that look absolutely mundane until the light energizes them. Then they glow electric shades of orange, pink and chartreuse.
The color of the light given off is determined by the amount of energy released as the chemical gets rid of its energy or "decays from an excited state," as chemists say. Each color in the rainbow has a different energy and they follow in order, with blue as the most energetic and red as the least. Scientists can use light intensity to investigate how glow-in-the-dark materials behave.
Scientists also study this behavior by looking at the amount of time it takes for each molecule to decay from an excited state. But this is more difficult, requiring a high-pulse rate laser and because the molecules don't all decay at the same time.
Because of changing lighting conditions, the technique of looking at the colors or the intensity (brightness) of the emitted light is difficult to repeat.
But the second lifetime method always gives the same result in any laboratory in any light conditions. For this reason, all of Demas' sensors use the lifetime technique to determine the luminescent properties of chemicals.
The basic principle of Demas' sensors is not too complicated.
First he decides what he wants to measure. For an oxygen sensor, he obviously wants to measure oxygen, and for a pH sensor he wants to measure the number of hydrogen ions in solution. He uses a molecule with special luminescent properties, in most cases an exotic metal, such as Ruthenium, surrounded by other atoms.
He chooses these molecules, called the analyte, because they react with whatever ion or molecule he wants to measure. When the ion reacts with the analyte, it changes the luminescent properties of the analyte very slightly. Demas then uses his "fast-pulse" laser and lifetime technique to quantify these changes. From the data he can determine exactly how much of a particular ion or molecule is in solution.
In actuality, the lifetime technique is the easiest and shortest part of the project. The most difficult part is trying to determine what analyte to use. In real life, chemists don't want to have weird metal molecules, or complexes, floating around in solution because these metals tend to interact with other molecules that the chemists don't want the metal to interact with. So they solve this problem by encasing the metal complex in a polymer, which prevents the metal from interacting when it's not supposed to. It also changes the luminescent properties of the metal molecule slightly, so tweaking can be done to make each analyte exactly right for each application.
Making cars work better
The Ford Motor Company uses the University's ingenious technique involving these oxygen sensors to determine the aerodynamic qualities of its cars. In the past, Ford used costly, time-consuming mechanical pressure sensor tubes attached to the walls of the car to determine stress points.
So how do they look at the aerodynamics of a car using oxygen sensors? The company takes advantage of the fact that air is made up of oxygen, among other things. In places where the air is compressed along the surface of a car, the air pressure (and therefore the oxygen molecule concentration) increases. Similarly, in places where the air expands the oxygen concentration decreases.
By covering a car in a special paint composed of the Demas group's oxygen-sensing polymers and sticking the car in a wind tunnel, scientists can look at the lifetimes of the luminescent molecules and determine exactly where pressures are greatest and least on the frame. This helps design more efficient and less noisy cars.
Helping trauma patients
William Bare, a graduate student researching pH sensors in Demas' group, explains how the sensors can be used in hospitals for medical monitoring.
"In a trauma ward, it's important to monitor blood pH," he says. Normally, doctors take periodic blood samples and test them in the lab, which requires time patients often don't have. With this novel type of pH sensor, "you could just stick a fiber optic cable like an IV into a patient and connect it to a read-out box the size of a cigarette carton. Blood pH could be monitored constantly," he says.
Demas stresses the method's safety. "The metal complexes are encased in polymers, which prevents them from interacting" with the patients' blood, he explains. He adds that there is not much of the metal there in the first place. "I could probably eat it straight," he jokes.
But there are limitations to this method.
Because the pH sensors have limited range, scientists must use more than one kind at a time to cover the entire pH scale.
Also, these sensor molecules are sensitive to oxygen as well as pH, so scientists must measure oxygen concentration to calibrate pH concentration.
Graduate student Bare and Demas both talk enthusiastically about applications in environmental monitoring and ecology. Their pH and oxygen sensors have a distinct advantage over previous testing methods - the sensors are easily automated.
Someday, a scientist could just place Demas' sensors in a pond and leave, collecting data from a remote computer. This is a vast improvement over the labor-intensive processes scientists currently use: collecting water samples on a daily basis and hauling them back for testing in a chemistry lab.
Airak Inc., a two-year-old company based in Manassas, Va., manufactures optical sensors and is currently working to develop monitoring systems with Demas' help.
Demas' "efforts here helped us move in the direction of commercializing water quality products that will help governments and institutions monitor water supplies," said Tim Mack, vice-president of marketing.
And the future of glow-in-the-dark sensors looks good.
"This is a very powerful analytical technique," Demas says. He believes it will "usurp ultimately most analytical techniques for monitoring systems."
This chemistry collaboration is not only successful at producing quality research, but also at enjoying the research they do. When asked to describe her colleagues, third-year Graduate student Heather Rowe smiles. "We're very quirky, but it's good stuff," she says.
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