Cryptand receptors in metal ion induced fluorescence signaling

Fluorescence signaling systems in the format, “Receptor–Spacer–Fluorophore” can be built for transition metal induced fluorescence enhancement. The quenching nature of paramagnetic transition metal ions can be overcome with cryptand receptors as they include the metal ion inside their cavity such that metal–fluorophore interactions responsible for quenching, are minimized. Suitably designed cryptand based systems can translocate a metal ion either from inside to outside the cavity or from one end to the other inside the cavity. Such translocation can be utilized for reversible fluorescence signaling. Cryptand receptors can also be derivatized with fluorophores having either donor or acceptor ability for studying Förster resonance energy transfer in single or multi-steps. Thus, cryptand receptors afford a large number of opportunities for potentially useful fluorescence signaling systems.