Dicyanostilbene-derived Two-photon Fluorescence Probe for Lead Ions

One-photon microscopy (OPM ) uses a single photon of higher energy to excite the fluorophore, while two-photon microscopy (TPM) uses two photons of lower energy as the excitation source. Therefore, TPM has such distinct advantages as improvement of penetration depth , localized two-photon excitation, reduction of photo-damage and photobleaching , small absorption coefficient of light in tissue, and lower tissue autofluorescence. These advantages make TPM more popular among biologists. Lead is a common contaminant and has inherent toxic effects on human health and environment. Pb2+ ion contamination can affect a wide variety of diseases such as anemia, irritability, memory loss, and muscle paralysis. For these reasons, there is an urgent need to develop some effective two-photon fluorescence probes to detect trace amounts of Pb2+ ions in live cells and tissues. A novel two-photon fluorescence probe for Pb2+ derived from 4-methyl-2, 5-dicyano-4'-amino stilbene as a two-photon fluorophore and bis [2-(2-aminophenylsulfanyls) ethyl] amine as a novel Pb2+ ligand was developed. The probe possessed small molecule size, large two-photon absorption cross-section (1020 GM) , noncytotoxic effect , long-wavelength emission at 609 nm, large Stokes shift(209 nm) , excellent photostability, moderate water-solubility , good cell-permeability and pH-insensitivity in the biologically relevant range. The probe was able to selectively detect Pb2+ ions in live cells and living tissues without inter-ference from other metal ions and the membrane-bound probes, and its quenching constant (K-sv(TP)) was 7. 58 x 10(5) L/mol.