Abstract: A biosensor for detecting the presence of a target analyte is disclosed. The biosensor is formed from microspheroidal particles which have had a binding partner for the target analyte immobilized on their surfaces. The binding partners may be nucleotides; peptides, proteins, enzymes, antibodies and so on. When the analyte binds to its partner, the whispering gallery mode (WGM) profiles of the micro spheroidal particles change such that the profile peaks undergo a red- or blue-shift. The immobilized binding partners may include fluorophores and the like so that they emit fluorescence, phosphorescence, incandescence and the like. These fluorophores may take the form of a nanocrystal or quantum dot.