A novel quinoline-based two-photon fluorescent probe for detecting Cd2+ in vitro and in vivo

A new two-photon fluorescent Cd2+ probe APQ is developed by introducing a N-1,N-1-dimethyl-N-2-(pyridin-2-ylmethyl)ethane-1,2-diamine binding group and a 4-methoxyphenylvinyl conjugation-enhancing group to the 2- and 6-positions of quinoline. This probe shows a large red shift and good emission enhancement under Cd2+ binding. It also exhibits a high ion selectivity for Cd2+ (especially over Zn2+) and a large two-photon absorption cross section at 710 nm. Two-photon microscopy imaging studies reveal that the new probe is non-toxic and cell-permeable and can be used to detect intracellular Cd2+ under two-photon excitation.