Aggregation-induced bimodal excitation of nitrogen-doped carbon dots for ratiometric sensing of new coccine and solid-state multicolor lighting.

Trace detection of foodstuff pigments have gained increasing attention because of their close association with biological and environmental processes. Herein, we propose an innovative bimodal excitation nitrogen-doped carbon dots (N-CDs) for ratiometric sensing of new coccine (NC) pigment, which are synthesized by using melamine and o-phenylenediamine as precursors via solvothermal treatment. With the increase of the N-CDs concentration, N-CDs exhibit not only a concentration-dependent tunable color behavior, but also a novel aggregation-induced bimodal excitation phenomenon. Considering this distinctive bimodal excitation behavior, a ratiometric sensor based on N-CDs has been developed for the detection of the NC in different organic solvents due to the inner filter effect and fluorescence resonance energy transfer. The intensity ratio of two excitation signals is linear with the NC concentration in the range of 0.032-100 µM, and the limit of detection is as low as 32.1 nM. Meanwhile, we realize the design of multicolor-emission N-CDs/polymer films. All in all, this work presents a novel kind view of the mechanism of distinctive bimodal excitation of N-CDs, and further proposes an innovative ratiometric method for the screening analysis of NC in food samples and environmental pollutants.