A water-soluble fluorescence “turn on” chemosensor for Cu2+ signaling: A combined photophysical and cell imaging study

Abstract A simple and effective fluorescence “turn on” chemosensor (ZPA) has been synthesized for rapid, sensitive and selective detection of copper ions (Cu 2+ ) in fully aqueous buffer. The binding interaction between ZPA and Cu 2+ was investigated through UV–vis absorption, fluorescence measurement, mass spectroscopy, and IR spectrum analysis. Cu 2+ could specifically bind with the hydroxyl-O and imine-N atom in ZPA with high affinity ( K a  = 6.08 × 10 7  M −1 ). Coordination of Cu 2+ to ZPA restricting the photoinduced electron transfer (PET) process in free ZPA and generating a more rigid ZPA/Cu 2+ complex with an extended π-electron conjugation system, sequentially leading to the fluorescence enhancement of ZPA. The detection limit (calculated to be 1.49 × 10 −8  M) was far below the limit in the World Health Organization (WHO) guidelines for drinking water (30 μM) and the sensing process was fully reversible. Practical applications of ZPA for Cu 2+ detection in real water samples were investigated with satisfactory results. Endowed with attributes like high binding affinity, specificity, relatively long excitation/emission properties and excellent bio-compatibility, ZPA demonstrated outstanding fluorescent imaging of intracellular Cu 2+ in living cells.