NOVEL FLUORESCENT PROBES FOR VISUALIZATION OF pH CHANGES AND Zn (Ⅱ) IONS IN LIVE CELLS

Abstract

Intracellular pH plays many significant roles in various cellular processes including cell proliferation, cell growth, apoptosis, signal transduction, and cellular metabolism. Lysosome is a membrane-bound organelle with pH 4.5-5.0 which is found in virtually all animal cells. Zn (II) ions extensively exist in human cells and body fluid. Research revealed that Zn (II) ions involved in many metabolism process such as cell growth, reproduction, and tissue regeneration. Near-infrared (NIR) fluorescent probes for the detection of intracellular pH and Zn (II) ions have become hot research topics because of the advantages of high sensitivity, easy operation, deep tissues penetration, real-time monitoring, and low background interference. In this dissertation, we reported two NIR fluorescent probes for sensing of intracellular Zn (II) ions. The probes show advantages of large Stokes shift, excellent photostability and good selectivity to Zn (II) over other metal ions. We also developed five coumarin-hybridized near-infrared fluorescent probes for sensing of lysosomal pH changes in both NIR and visible regions. We significantly improved compatibility and water-solubility of the probes by introducing oligo(ethylene glycol) to the fluorophores. In order to overcome fluorescence quenching issue of cyanine dye (IR-780) in aqueous solution, we successfully developed a fluorescent cassette by introducing tetraphenylethene (TPE) derivative to dye IR-780 through an ether bond connection. Both TPE donor and cyanine acceptor in the cassette show significant fluorescence enhancement when the fluorescent cassette becomes aggregated in aqueous solutions. The fluorescent cassette has been used to detect intracellular pH changes in live cells through manipulation of the cassette aggregation status by pH changes. In order to overcome systematic errors of intensity-based fluorescent probes, we also developed three ratiometric fluorescent probes based on BODIPY donors and near-infrared rhodamine or hemicyanine acceptors through electric wire pi-conjugation connections in a through-bond energy transfer approach The probes display ratiometric fluorescence responses to pH decreases from 7.4 to 2.4 with fluorescence decreases of BODIPY donors and fluorescence increases of rhodamine or hemicyanine acceptors.