Highly Sensitive and Selective Photoluminescence Detection of Copper Ions via In Situ Formation of Fluorescent Polydopamine

Abstract

Detection of heavy metals via fluorescence has attracted increasing attention. Herein, we report a novel copper(II) ion (Cu2+) sensor using fluorescent polydopamine (FPDA). Dopamine is easily oxidized to polydopamine by oxygen in alkaline solution, and oxidized polydopamine does not fluoresce. However, under a nitrogen atmosphere, FPDA can be produced by adding hydrogen peroxide into a dopamine solution in the presence of Cu2+ ions. The fluorescence intensity of FPDA is strongly dependent on the concentration of Cu2+ ions. At higher concentrations of Cu2+ ions, the photoluminescence intensity of FPDA also increases at a higher rate. FPDA exhibited a highly sensitive and selective response to Cu2+ ions over other ionic competitors in the biological milieu, achieving a detection limit as low as 1 nmol L-1 (nM). This study shows that the method can be used for monitoring in vivo Cu2+ ions owing to the distinct properties of FPDA such as strong fluorescence signal and biocompatibility.