Red Dual-Emissive Carbon Dots for Cu²⁺ Selective Detection and Dynamical Monitoring

Monitoring the copper ion (Cu 2+ ) levels has attracted considerable attention due to its significance in environmental and physiological applications. Here, we report on red dual-emission carbon dots (CDs) with a 43% quantum yield and without excitation wavelength dependence for probing Cu 2+ in vitro and in vivo. The solid coordination of Cu 2+ with the surface groups of CDs generates an asynchronous fluorescent quenching of CDs and enables ultrasensitive detection of Cu 2+ in vitro. The intensity ratio of fluorescence at 605 and 650 nm ( F 605 / F 650 ) shows a linear response to Cu 2+ concentration ranging from 0 to 1.1 μM, with an ultralow detection sensitivity of 0.58 nM. Moreover, the as-prepared CDs show good stability, anti-interference capability, low cellular toxicity, and exceptional ability to penetrate plant cell walls, endowing the CDs with excellent bioimaging potentials and tracking the dynamic levels of Cu 2+ in living cells.