Cyclic peptides as well as modified EF-hand of calmodulin have been newly designed to achieve high affinity towards uranyl(VI). Cyclic peptides may be engineered to bind uranyl(VI) to its backbone under acidic condition, which may enhance its selectivity. For the modified EF-Hand motif of calmodulin, strong electrostatic interactions between uranyl(VI) and negatively charged side chains play important role in achieving high affinity, however, it is also essential to have secondary structure element and formation of hydrophobic cores in the metal-bound state of the peptide.