a process for the production of fluorescent nanoparticles selected from noble metal , silica or polymer nanoparticles which comprises : 1 . a process for the production of fluorescent nanoparticles selected from noble metal or silica nanoparticles which comprises : providing a platform of nanoparticles ; covering the surfaces of the nanoparticles to saturation with thiol - terminated polymers by one of the following methods : 1 . mixing the nanoparticles with methoxy -- thiol and biotin -- thiol ; 2 . mixing the nanoparticles with fluorescently - labeled methoxy -- thiol and / or biotin -- thiol 3 . coordinating thiol and biotin thiol to the surfaces of the nanoparticles by a non - covalent bond ; and 4 . directly conjugating methoxy - thiol and biotin - thiol to the surfaces of the nanoparticles , so that the polymers bind to the surfaces of the nanoparticles as a brush layer via thiol particle coordination of the thiol ends so that the biotin or methoxy ends are free ; and homogeneously mixing the resulting biotin nanoparticles with fluorescent avidin or a derivative thereof in proportions such that the final concentration is 1 biotin molecule for every 10 to 1000 avidin molecules in the fluorescent multi - coloured nanoparticle - avidin complexes , each being capable of having a different targeting molecule , and which may be mixed with biotin related targets , and the fluorescent labeled avidin or a derivative thereof being spaced away from the particle surface , thus reducing or removing the potential quenching of the dye .