Facile reflux synthesis of polyethyleneimine-capped fluorescent carbon dots for sequential bioassays toward Cu²⁺/H₂S and its application for a logic system

In this work, we present a novel facile strategy for green synthesis of polyethyleneimine (PEI)-capped carbon dots (PEI-CDs), in which citric acid and PEI were chosen as reactants and highly fluorescent PEI-CDs could be readily obtained via a simple one-pot refluxing under 120 °C within 2 H. Fluorescence studies indicate that the as-prepared PEI-CDs exhibit strong fluorescence emission at 446 nm with excitation at 365 nm. Upon the sequential addition of Cu²⁺ and H₂S, PEI-CDs result in an interesting “ON−OFF−ON” three-state emission responses, promising a bifunctional sensory platform. Moreover, the Cu²⁺/H₂S-facilated reversible fluorescence changes of PEI-CDs have demonstrated the design of an INHIBIT logic system based on Boolean logic.