Facile preparation of a hydrophilic Eu-based ratiometric fluorescent nanosensor for Cu ion detection and imaging in living cells.

In this work, a hydrophilic Eu-based ratiometric fluorescent nanosensor (PAAC-Eu) was developed for Cu ion detection in aqueous solutions and imaging in living cells. The sensor was prepared a simple one-step reaction at room temperature, leveraging the synergistic coordination of commercially accessible polyacrylic acid (PAA) and coumarin-3-carboxylic acid (CCAH) with Eu ions. PAAC-Eu was easy to disperse in aqueous media and exhibited two characteristic emission bands at 406 nm and 618 nm, respectively, upon excitation at 350 nm. Cu ions could bind with the free carboxyl groups in PAAC-Eu within 10 min, leading to a decrease in fluorescence at 618 nm () and a negligible effect on fluorescence at 406 nm (). Accordingly, a rapid, sensitive and selective method for detecting Cu ions was established, which could complete Cu ion assay within 30 min. A good linear relationship was observed between / and Cu ion concentration at 0-20.0 μM (0-1.28 mg L) with a detection limit as low as 0.175 μM (11.2 μg L). The proposed method was successfully applied to quantify Cu ions in real water samples. Moreover, a portable paper-based sensor was developed by loading PAAC-Eu in filter paper, which could enable visual detection of Cu ions without using large instruments. Finally, cell experiments demonstrated the low cytotoxicity and good cell permeability of PAAC-Eu, and ratiometric fluorescence imaging of Cu ions in living cells was successfully performed.