Two-photon Fluorescent Probes Based On Quinoline And Their Bio-imaging In Living Cells

Fluorescent probes are important tools for detecting metal ions and small molecules in vivo. Due to their high selectivity and sensitivity, simple synthesis, inexpensive and good nature of biological applications, they gradually become the main detection tools. The results of chemical reactions involving in fluorescent probes and the biological active substances in vivo can help us to understand life activities from the microscopic point of view better. In recent years, the application of fluorescence detection technique including the clinical diagnosis, biological imaging, and environmental protection. However, most of the fluorescent probes are single-photon, these probes are easy to get interfered by auto-fluorescence and cells-photodamaged and photobleached due to short excitation. Compared with conventional single-photon fluorescent probes, two-photon fluorescent probes as a research interest, gradually began to replace the single-photon fluorescent probes. Two-photon fluorescent probes have the ability to penetrate deeper into the tissue; they can also provide higher spatial resolution and localized excitations in the near-infrared spectral region (700-1000nm). Long-wave excitation could avoid photobleaching and photodamage to biological samples, affording high contrast three-dimensional (3D) images. Specifically, two-photon confocal imaging can extend the unique advantages of living cells and tissues observation time, which makes biological scientists observe living cells or tissues of life processes better. Among the fluorescent reporter groups, a quinoline derivative is increasingly used in biological experimentsdue to its excellent properties, water solubility, low toxicity and easy modification characteristics.In this paper, we used quinoline as the platform, successfully designed and synthesized a series of selective recognition of Cd2+and Cys/Hcy two-photon fluorescent probes with Sonogashira coupling and other organic chemical reactions. The target molecules were characterized by’HNMR spectroscopy and mass spectrometry.1. On basis of quinoline, a novel two-photon fluorescent probe, Lyso-QSl, selective for lysosomes in live cells, have been synthesized. Based on ICT and PET, this probe exhibits large emission shift and good emission enhancement upon binding with Cd2+. It can easily loaded into cells for visualization of lysosomes in live cells for a long period of time through two-photon microscopy and presented satisfactory results for the imaging of Cd2+in lysosomes of live cells, is first reported. Colocalization studies of the probe with commercial Lysotracker Green in Bel-7402cells demonstrated the specific localization of the probe in the lysosomes with an extremely high colocalization coefficient (0.90).2. A ratiometric two-photon fluorescent probe (MQ) was designed and synthetized for the detection of cysteine (Cys) and homocysteine (Hey) with high selectivity. MQ exhibited large two-photon absorption cross-section at710nm (265GM) as well as a significant blue shift (about95nm) of fluorescent spectrum on addition of Cys or Hey. MQ responsed to Cys/Hcy much faster than previous two-photon fluroescent probes for Cys/Hcy. The response mechanism was proved by’H NMR, Maldi-TOF MS and theoretic calculation. Cell cytotoxicity and bio-imaging studies revealed that MQ was cell-permeable and could be used to detect Cys with low cytotoxicity under two-photon excitation.