Developing novel methods for metal-induced switching of peptide structures expands the design principles of functional biomolecules and biomaterials. Here, a simple method for on-resin synthesis of dipicolylamine (Dpa)-containing peptides was developed. Whereas addition of divalent metal ions such as Fe(ii) and Cu(ii) to a peptide bearing a pair of Dpa moieties at the i and i + 4 positions led to the formation of a 1:1 complex of Dpa with metals, addition of Ni(ii) yielded a cross-linked structure of Dpa-metal (2:1). This feature was utilized for the selective detection of Ni(ii) using the peptide-Fe(ii) complex. Repeated switching of the helical structure was also achieved by multiple additions of divalent metal ions to the peptide.