Excitation energy transfer from polystyrene to dye in 40-nm diameter microspheres

When dye molecules are placed into a solid, like a polymer matrix, the opportunity exists for resonant excitation energy transfer from the solid to the dye. We observe a 51% excitation transfer efficiency from polystyrene to the fluorescent dye BODIPY® 564/591 in 40-nm polystyrene microspheres manufactured for use as fluorescent bioprobes. The Förster radius for this transfer is 19 Å. Despite this modest value for R₀, the high concentration of dye in these spheres permits efficient excitation transfer. Absorption, fluorescence, and fluorescence excitation spectra for the polystyrene spheres with and without dye are reported. Our work highlights the idea that the solid need not just be a structural entity in the creation of a fluorescent material. It can play the role of an element in an excitation transfer network. The solid's absorption of light can sensitize fluorescence from the dye molecules through excitation transfer, increasing the overall emission of the dye. Application to the area of biological fluorescence probe development is discussed.