The present invention relates to a method of producing a fluorescent
polypeptide complex characterized in that an isolated fluorescent
polypeptide is inter-molecularly cross-linked with itself or one or more
other polypeptides and wherein said complex is of 40 nm to 500 nm in
size, it also relates to a complex obtainable by such method, to
conjugates comprising such a fluorescent polypeptide complex and to the
use of such complex or conjugate.