This invention provides a donor bead for use in an assay, wherein the bead (a) is coated with a layer of hydrogel having directly or indirectly bound thereto a polyacrylamide-supported sugar or a polyacrylamide-supported glycan, and (b) comprises a photosensitizer which, upon excitation by laser light of a suitable wavelength, converts ambient oxygen to singlet state oxygen. This invention also provides an acceptor bead for use in an assay, wherein the bead (a) is coated with a layer of hydrogel having directly or indirectly bound thereto a polyacrylamide-supported sugar or a polyacrylamide-supported glycan, and (b) comprises a chemiluminescer and a fluorophore, whereby when the bead is contacted with singlet state oxygen, the singlet state oxygen reacts with the chemiluminescer which in turn activates the fluorophore so as to cause the emission of light of a predetermined wavelength. This invention further provides related kits, detection methods and characterization methods.