Two zinc finger peptides, namely ZFQD(Ln) and ZFQE(Ln) (Ln = Tb or Gd), with an appended Ln(3+) chelate and a phosphoserine able to coordinate the Ln(3+) ion are presented. The two peptides differ by the amino acid anchorage of the chelate, either aspartate (D) or glutamate (E). Both peptides are able to bind Zn2+ and adopt the beta beta alpha fold. Interestingly, ZFQE(Tb) shows a decrease in sensitized Tb3+ luminescence upon Zn2+ binding whereas ZFQD(Tb) does not. The luminescence change upon Zn2+ binding is attributed to a change in hydration number (q) of the Tb3+ ion due to the decoordination of the phosphoserine from the Ln(3+) ion upon Zn2+ binding and peptide folding. This process is highly sensitive to the length of the linker between the Ln chelate and the peptidic backbone. The magnetic properties of the gadolinium analogue ZFQE(Gd) were studied. An impressive relaxivity increase of 140% is observed at 60 MHz and 25 degrees C upon Zn2+ binding. These changes can be attributed to a combined increase effect of the hydration number of Gd3+ and of the rigidity of the system upon Zn2+ binding. Phantom MR images at 9.4 T show a clear signal enhancement in the presence of Zn2+. These zinc finger peptides offer a unique platform to design such Zn-responsive probes.