University of Rochester researchers announce in the current issue of Applied Optics a technique that in 60 seconds or less measures multiple chemicals in body fluids, using a laser, white light, and a reflective tube. The technique tests urine and blood serum for common chemicals important to monitoring and treatment of diabetes and cardiovascular, kidney, urinary and other diseases, and lends itself to the development of fast batch testing in hospitals and other clinical settings.
Co-researchers Andrew J. Berger, associate professor of optics, and Dahu Qi, doctoral candidate, used low-refractive-index tubes instead of cuvettes or other bulky containers for holding biological specimens. And, to get more information from the fluids, they used white light?like that from an ordinary light bulb?along with the laser. The tubes and light bulbs made all the difference.
In the laser technique called Raman spectroscopy, scientists shine laser light onto molecules and the light scatters off, gaining or losing energy. A spectrograph translates the changed energies into spectra. Each chemical presents a Raman spectrum that scientists recognize. The Raman approach is a favorite for finding chemicals that overlap and mix in fluid, much like musical instruments in an orchestra. But Raman spectroscopy comes with a problem.
Raman signal is notoriously weak. Using it to test biofluids, with their lighter chemical concentrations than in many fluids, is not a natural choice. Berger and Qi injected fluid samples into a thin transparent tube specially made to contain the light, and the tubes long path length of interaction let the scientists collect more Raman scattering. "The tubes have a refractive index lower than water, so the light bounces along inside the liquid core, just as in solid optical fibers for telecommunications," said Berger. "Other groups had used these fibers to strengthen their Raman signals, so we wanted to see if we could translate that advantage
Contact: Jennifer Wettlaufer
University of Rochester