Novel compositions and methods are provided for detecting the presence of a material of interest in a specimen on a solid surface. A composition useful for detecting the presence of a material of interest in a specimen comprises (1) a detector conjugate comprising a fluorescing moiety bonded to a compound capable of specific binding with the material of interest, or a derivative thereof, and (2) a non-detector conjugate comprising a poly(amino acid) and a compound having substantial structural and charge similarity to the fluorescing compound and no observable fluorescence, or low level fluorescence of a different wavelength than that of the fluoresing compound, in the region of fluorescence of the fluorescing compound. In the method of the invention, a specimen, on a solid surface, is combined with the detector conjugate and the non-detector conjugate, and the combination is incubated. Unbound conjugates are removed from the solid surface by washing and then the surface is irradiated with light having a wave length absorbed by the fluorescing compound. The fluorescent light emitted by the combination is observed and is a function of the amount of the material of interest present in the specimen.