From detecting biological weapons to diagnosing disease to environmental monitoring, fluorescence has been used for all kinds of tests. However, sometimes it’s difficult to discriminate the fluorescent dye from cells and tissues that also fluoresce. Measuring how long the fluorescence lasts is one way to overcome this, but not many dyes have clearly distinguishable fluorescence lifetimes, so researchers at Kimberly-Clark Worldwide Inc. in Roswell, Ga., are working with phosphorescent particles instead.Encapsulating these phosphorescent particles keeps them oxygen-free, so that their phosphorescence is bright and long-lasting, even in biochemical solutions. The image is false-colored green.Although phosphorescence has been observed since ancient times, its biological applications have been limited because it works best without oxygen. Thus, the researchers encapsulated phosphorescent particles so that they are separated from the oxygen-rich environment of the cell. To do this, they used a polymer coating that contained one or more halogens, such as fluorine or chlorine.The phosphorescent particles consisted of a porphyrin bound to either platinum or palladium. They phosphoresce when stimulated at the visible red wavelengths 650 and 670 nm, respectively. The researchers examined the particles with the phosphorescence detector accessory of a Horiba Jobin Yvon fluorescence spectrometer.As reported in the May 30 online publication of Analytical Chemistry, they observed that the encapsulated particles phosphoresced brightly and that the glow lasted a long time, with almost the same brightness and length of time as when the phosphorescent particles were not encapsulated but were in an oxygen-free solution.They tagged the encapsulated phosphorescent particles with an antibody for C-reactive protein, which is involved with inflammation, and demonstrated that the particles can be used to detect the protein. This result shows that these particles can work in a real biochemical assay.The researchers noted additional benefits of the encapsulated particles — namely that they are stable in water and can be excited with low-cost LEDs.