The interaction between synthetic materials and biomolecules plays an important role in biomedical and pathological sciences. An important issue in these interactions is control of stoichiometry. The interaction between NTA ligands and proteins with six consecutive His residues has been widely used for protein purification. Control of stoichiometry is an important issue in applying this recognition strategy to the creation of defined nanoparticle-protein conjugates. In this communication we report the direct control of particle-protein stoichiometry through variation of nickel chloride concentration, as demonstrated through fluorescence and gel electrophoresis.