Facile preparation of a hydrophilic Eu-based ratiometric fluorescence nanosensor for Cu2+ ion detection and living cells imaging

Abstract

In this work, a hydrophilic Eu-based ratiometric fluorescence nanosensor (PAAC-Eu) was developed for Cu2+ ion detection in aqueous solution and imaging in living cells. The sensor was prepared via 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 Eu3+ ion. PAAC-Eu was easy to disperse in aqueous media and exhibited two characteristic emissions at 406 nm and 618 nm, respectively, upon excited at 350 nm. Cu2+ ion could bind with the free carboxyl groups in PAAC-Eu within 10 min leading to a decrease in the fluorescence at 618nm (I618), but negligible effect on the fluorescence at 406 nm (I406). Accordingly, a rapid, sensitive and selective method for detecting Cu2+ ion was established. By this method, Cu2+ ion assay could be completed within 30 min. A good linear relationship was obtained between I406/I618 and Cu2+ ion concentration at 0-20.0 μM (0-1.28 mg L-1) with the detection limit as low as 0.175 μM (11.2 μg L-1). The proposed method has been successfully applied to quantify Cu2+ ion in real water samples. Moreover, a portable paper-based sensor was exploited by loading PAAC-Eu in filter paper, by which the visual detection of Cu2+ ion could be achieved independent of large instruments. Finally, cell experiments have demonstrated the low cytotoxicity and good cell-permeability of PAAC-Eu, and it has been successfully used for ratiometric fluorescence imaging of Cu2+ ion in living cells.