Taking the temperature

US researchers have developed a fluorescent material that could be the basis for highly sensitive optical thermometers useful in biological monitoring, medical, industrial and security applications.

University of California scientists working at Los Alamos National Laboratory have developed a fluorescent material that responds rapidly and reversibly to temperature. The material could be the basis for highly sensitive optical thermometers useful in biological monitoring, medical, industrial and security applications.

Although molecule-based optical thermometers have received a great deal of attention recently, most have limited operational ranges on the order of only a few degrees. The Los Alamos thermometer is accurate to one-tenth of a degree and responds to temperature changes ranging from 77 to 284 degrees Fahrenheit, giving it a wider temperature range than any existing fluorescent thermometer.

The new thermometer employs a luminescent molecule – a luminophore – within an ionic liquid. The smallest drop of the ionic liquid contains trillions of these individual molecular reporters. When the luminophores are illuminated with ultraviolet light, one of its components glows in the ultraviolet (375 nanometre) range of the visible spectrum and another component glows a different – blue -colour near 475 nm. The relative intensities of these two bands of light changes dramatically with temperature, thereby creating a colour that corresponds with specific temperatures.

According to Laboratory scientist Sheila Baker, “this kind of optical thermometer has the potential for use on so many scales – large and small- that we have only just scratched the surface of its countless possible applications. For example, when used in a manufacturing setting, the molecular thermometer’s real-time monitoring capability may help to optimise industrial processing leading to waste minimisation and energy conservation. On the microscale, this technology could be used for mapping temperature in lab-on-a-chip and microelectromechanical systems and for locating heat bottlenecks in integrated circuits. When coupled with flexible fabrics, a reliable bedside and battlefield temperature monitoring device could be created.”

In addition to Baker, Los Alamos Frederick Reines postdoc Gary Baker, and technical staff member T. Mark McCleskey worked on the development of the thermometer. The researchers are currently working to advance several promising applications, as well as encapsulating the material to create temperature-sensitive paints.