Inert phosphorescent nanospheres as markers for optical assays

A simple encapsulation technique is presented to produce highly phosphoresc ent, inert nanospheres that are suitable luminescent markers. It is based o n the coprecipitation of phosphorescent ruthenium(II)-tris(polypyridyl) com plexes and polyacrylonitrile, (PAN) derivatives from a solution in IV V-dim ethylformamide. The beads precipitate in the form of very small aggregates of spherical shape and a typical particle diameter of less than 50 nm. This process allows the encapsulation of phosphorescent and fluorescent dyes in an individual nanosphere provided that they are sufficiently lipophilic. Q uenching by oxygen is negligible due to the use of PAN. The nanospheres wer e characterized with respect to their spectral properties (quantum yields o f the luminophores, brightness, luminescence decay time), stability in aque ous buffered suspensions, and in terms of size, shape, and surface charge o f the particles, as well as storage stability, quenching by oxygen, and dye leaching.