Electrochemically active probes containing a tetraalkylated p-phenylenediamine redox responsive moiety and thiophene ligands were found to be sensitive to calcium ions. The electrochemical studies revealed that these compounds were able to bind Ca2+ ions. The redox properties of the transducer underwent dramatic changes upon calcium chelation provoking large oxidation potential shifts comprised between 549 and 911 mV. A high selectivity towards Ca2+ over Zn2+ was observed. The zinc complex was found to spontaneously undergo metal ion exchange in presence of Ca2+ yielding [Ca(L)(2)](2+).