Originally Published MDDI October 2005
A laser-based gas sensor could detect myriad diseases from samples of a patient's breath, according to researchers at Rice University in Houston.
Researchers at The Johns Hopkins University recently discovered a critical connection between the level of carbonyl sulfide in lung transplant patients and the likelihood of rejection. Frank K. Tittel of Rice's Laser Science Group collaborated with doctors at Baylor College of Medicine (Houston) and Johns Hopkins to better study the connection.
The team measured transplant patients' breath using a quantum cascade (QC) laser that can detect trace amounts of various gases. They found that patients who were not rejecting the lung had 1–50 ppb of carbonyl sulfide in their bodies. Those who were rejecting the lung had much higher levels, from 100 to several hundred parts per billion of carbonyl sulfide.
Tittel is confident that there are even more unexplored uses for detecting disease using the laser. “At this point,” he says, “there are approximately 400 diseases that have gas as biomarkers.” For example, he says, trace gases such as nitric oxide could indicate an airway inflammation.
Further, he explains, the test procedure is simple and quick. The process of collecting air samples from a patient might involve a simple mouthpiece, and the analysis is done in real time. “What could take days in terms of collecting and analyzing samples in a lab, the QC laser does almost immediately with as much reliability,” Tittel says.
QC lasers were invented nearly 40 years ago and have been used in many industries. They also can perform remote sensing of environmental gases and pollutants.
The laser is a very small sliver of semiconductor material. Electrons inside the material are contained within quantum wells that are made of gallium and aluminum. The wells are only nanometers thick, and within them the electrons behave according to quantum mechanics. That is, they jump from one energy level to another rather than move smoothly. They also tunnel through the layers rather than going over them. Light photons are emitted as the electrons jump. The range, power, and ability to work at room temperature make the laser suitable for remote sensing of gases and vapors.
Gases and vapors have characteristic chemical absorption patterns called fingerprints that consist of well-defined rotational and vibrational lines, Tittel explains. “The QC laser can be tuned to specific frequencies or wavelengths that correspond to specific rotational lines of different kinds of gases, thereby determining the type and amount of gas that is present.”
Although the technology is available, there are yet to be any medical devices that use it. NASA is funding work to use the technology on spacecrafts. Tittel hopes the platform technology will be applicable in a number of areas, from semiconductors to environmental work.
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