In this study, fluorescent proteins (FPs) were engineered to self-assemble into protein particles inside recombinant Escherichia coli while mediating the display of various protein functionalities such as maltose binding protein or IgG binding domains of Protein A or G, respectively. Escherichia coli produced functional FP particles of up to 30% of cellular dry weight. The use of respective FP particles displaying certain binding domains in diagnostics and as bioseparation resins was demonstrated by direct comparison to commercial offerings. It was demonstrated that variable extensions (AVTS, FHKP, LAVG, or TS) of the N-terminus of FPs (GFP, YFP, CFP, HcRed) in combination with large C-terminal extensions such as translational fusion of the polyester synthase from Ralstonia eutropha or an aldolase from Escherichia coli led to extensive intracellular self-assembly of strongly fluorescent fusion protein particles of oval shape (0.5×1 μm). The strong fluorescent label of these bioparticles in combination with covalent display of protein functions provides a molecular toolbox for the design of self-assembled microparticles suitable for antibody-capture or ligand binding based diagnostic assays as well as the high affinity purification of target compounds such as antibodies.