ANALYTICAL COMPOSITION AND METHOD

An optically detectable analytical composition comprising a rare earth dopant, a carrier incorporating the rare earth dopant, and at least one of: a chemical linker suitable to bind to a biological binding agent and a biological binding agent is disclosed. Preferred embodiments include a glass micro bead carrier treated to attach a biological binding agent such as a protein, or a nucleic acid. The binding agent can bind to a target species in a sample and thereafter be used to determine the presence, concentration or absence of the target in the sample. The composition can be used in a number of different applications, such as to perform fragment analysis of DNA. The narrow bands emitted by rare earth dopants when excited, allows for a large number of such dopants to be incorporated into an individual carrier, allowing detailed characterisation of the sample to be conducted in a reduced number of sample test runs.