We have synthesized nitrilotriacetic acid end-functionalized polystyrene (NTA-PS) for the controlled bioconjugation with histidine-tagged green fluorescence proteins (His(6)-GFP). NTA-PS was prepared using initiators containing tert-butyl protected NTA moiety via atom transfer radical polymerization (ATRP) of styrene; the protected tert-butyl group was subsequently removed at the a-chain end of polystyrene. The structure of NTA PS was characterized using H-1 NMR, C-13 NMR, and GPC. NTA chain ends of the polystyrenes were complexed with Ni2+ to produce Ni-NTA-PS, of which the specific binding properties were studied by forming spherical aggregates with His(6)-GFP in aqueous phase. The reversible association of His(6)-GFP with polystyrene spherical aggregates (with Ni2+) was controlled with imidazole and monitored with fluorescence microscope. Again, Ni-NTA-PS produced well-defined micelles with His(6)-GFP in water/DMF (DMF 4 vol %) and the size of micelles decreased when excess imidazole was added.