Temperature-Driven Metalloprotein-Based Hybrid Hydrogels for Selective and Reversible Removal of Cadmium(II) from Water

To develop biomaterials that easily and reversibly remove trace amounts of metal ions, we synthesized PNIPAM-co-CadRP, a thermally sensitive hybrid hydrogel by immobilizing a reconstituted cadmium binding peptide (CadRP) derived from the metalloregulatory protein CadR in a poly(N-isopropylacrylamide) (PNIPAM) gel network. The hybrid hydrogel retains the properties of the immobilized peptide and highly sensitively and selectively binds Cd(II) ions. The thermally sensitive properties of the hybrid hydrogel, which swells at low temperatures (<34 °C) and shrinks at high temperatures, provides a driving force sufficient to alternate the conformation of the immobilized CadRP such that the peptide captures and releases metal ions at high and low temperatures, respectively. Using this novel hybrid gel, we captured nanomolar Cd(II) from samples of environmental water in a highly efficient manner, leading to a practical and repeatedly reusable material to remediate our environment.