Measuring Chemicals in Body Fluids -- MEDICA - World Forum for Medicine

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.

The researchers 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. However, Raman spectroscopy comes along with a problem: The signal is notoriously weak.

Thus the researchers injected fluid samples into a thin transparent tube specially made to contain the light, and the tube’s long path length of interaction let the scientists collect more Raman scattering. They did get the stronger signal they were looking for, but the increase threw off measurements when samples of urine or blood serum varied in colour.

"We can’t neglect that body fluid samples absorb light," said said Andrew J. Berger from the University of Rochester. "We’d have two different samples with the same amount of protein and not get the same strength of signal." The solution was a beam of white light which the scientists send through each sample. It was easy enough to inject the light by using the end of the tube opposite the laser. The resulting corrections made chemical predictions significantly more accurate.

The team measured eleven chemicals in blood serum, such as total protein and cholesterol. In urine, they identified urea nitrogen and creatinine. Spectral tests use no chemical reagents and therefore offer the advantage of being nondestructive to fluid samples, unlike many lab tests.; Source: University of Rochester