Nucleus-targeting pH-Responsive carbon dots for fast nucleus pH detection

Nucleus pH is closely linked to many diseases such as aging, heart disease, skeletal myopathies, cancer, Alzheimer's disease, etc. Nevertheless, fluorescent sensors that can directly monitor nucleus pH changes have not yet been reported. Here, we first reported a green emissive carbon dots (CDs) for nucleus pH detection in living cells. CDs can selectively target nucleus with high accumulation at nucleolus due to their high affinity towards RNA once entering cells by lipid raft mediated endocytosis. Without washing, CDs at 5 μg/mL was enough to lighten nucleus within 10 min with the fluorescence on ever after 24 h incubation, achieving fast, wash-free, and long-term nucleus/nucleolus imaging. Meanwhile, the luminescent intensity of CDs was reduced gradually when pH changed continuously from 1 to 12, showing a pH-responsive fluorescence property with two linear ranges of pH 2-7 and pH 7-12. With their nucleus-targeting ability and pH-dependent photoluminescent property, CDs was successfully leveraged for nucleus pH detection in A549 cells and for in vivo pH sensing in zebra fish. CDs present a promising and powerful fluorescent sensor for nucleus imaging and nucleus pH sensing in living cells on the way to understand nucleus-related biological events.