Hierarchical MOF Nanocomposite Enables Fluorescence Imaging and Valence Discrimination of Cu+/Cu2+ in Copper Homeostasis

Abstract Copper homeostasis refers to the cellular balance of copper ions, which is disrupted by copper excess or deficiency. The simultaneous detection of intracellular Cu+ and Cu2+ reveals changes in copper valence states during disruption of copper homeostasis. Therefore, a hierarchical dual-emission fluorescent nanoprobe was designed for simultaneous detection and imaging of Cu+ and Cu2+. A rhodamine derivative for Cu2+ detection was encapsulated within ZIF-8 and the outer surface was coated with polydopamine (PDA) onto which a naphthalimide-based Cu+ probe was adsorbed to construct the Rbh@ZIF-8@PDA/CuL (RZPC) nanoprobe. Cu2+ induces the ring-opening reaction of the rhodamine derivative and generates a strong fluorescence signal. The fluorescence of the naphthalimide moiety is quenched by the photoinduced electron transfer (PET) effect upon binding to Cu+. The probe exhibits rapid response and shows no cross-interference between the two detection channels. The detection limits for Cu+ and Cu2+ were 0.004 μM and 0.008 μM, respectively. The ability of the probe to respond to endogenous and exogenous copper ions was validated using copper chelators, as well as exogenous copper supplementation. Finally, the nanoprobe was successfully applied to monitor the changes in intracellular Cu+ and Cu2+ during ES/DSF-induced cuproptosis and to evaluate Cu+/Cu2+ alterations across different cell models.