Self-assembling NBD-tripeptide as a dual-mode colorimetric platform for naked eye and smartphone joint detection of micro to nanomolar Copper(II) ions.

Compared to conventionally synthesized organic compounds, peptides with amphiphiles have unique advantages, especially in self-assembly. Herein, we reported a peptide-based molecule rationally designed for the visual detection of copper ions (Cu2+) in multiple modes. The peptide exhibited excellent stability, high luminescence efficiency, and environmentally responsive molecular self-assembly in water. In the presence of Cu2+, the peptide undergoes an ionic coordination interaction and a coordination-driven self-assembly process that leads to the quenching of fluorescence and the formation of aggregates. Therefore, the concentration of Cu2+ can be determined by the residual fluorescence intensity and the color difference between peptide and competing chromogenic agents before and after Cu2+ incorporation. More importantly, this variation in fluorescence and color can be presented visually, thus allowing qualitative and quantitative analysis of Cu2+ based on the naked eye and smartphones. Overall, our study not only extends the application of self-assembling peptides but also provides a universal method for dual-mode visual detection of Cu2+, which would significantly promote point-of-care testing (POCT) of metal ions in pharmaceuticals, food, and drinking water.