Layer-by-Layer Deposition with Polymers Containing Nitrilotriacetate, A Convenient Route to Fabricate Metal- and Protein-Binding Films

This paper describes a convenient synthesis of nitrilotriacetate (NTA)-containing polymers and subsequent layer by-layer adsorption of these polymers on flat surfaces and in membrane pores. The resulting films form NTA metal-ion complexes and capture 2-3 mmol of metal ions per mL of film. Moreover, these coatings bind multilayers of polyhistidine-tagged proteins through association with NTA-metal-ion complexes. Inclusion of acrylic acid repeat units in NTA-containing copolymers promotes swelling to increase protein binding in films on Au-coated wafers. Adsorption of NTA-containing films in porous nylon membranes gives materials that capture similar to 46 mg of His-tagged ubiquitin per mL. However, the binding capacity decreases with the protein molecular weight. Due to the high affinity of NTA for metal ions, the modified membranes show modest leaching of Ni2+ in binding and rinsing buffers. Adsorption of NTA-containing polymers is a simple method to create metal- and protein-binding films and may, with future enhancement of stability, facilitate development of disposable membranes that rapidly purify tagged proteins.