Architecting ultra-bright silanized carbon dots by alleviating the spin-orbit coupling effect: a specific fluorescent nanoprobe to label dead cells

Developing high-performance carbon dots (CDs) with high photoluminescence quantum yield, excellent stability, and good biocompatibility as well as explore the related luminescence mechanism is still an urgent problem to be solved at present. Herein, we develop a new class of green-emitting silanized carbon dots (Si-CDs) featuring average size of ~ 2.8 nm, ultrahigh photoluminescence quantum yield of ~ 93%, robust photostability, and low cytotoxicity by high-temperature dehalogenation/polymerization process. Our experiments verify the dehalogenation process can alleviate the spin–orbit coupling (SOC) effect of heavy-atom-rich organic fluorophores with severe intersystem crossing through high-temperature hydrothermal reaction, meanwhile, the possibility of transition from the excited state (S1) to triplet state (T1) in the Si-CDs is significantly reduced, thus enhancing the fluorescence intensity and prolong fluorescent lifetime of Si-CDs. Besides, multiple fluorescent emitters can be integrated into one nanodot to effectively enhance the emission intensity by cross-linking polymerization. Owing to good optical properties of the obtained Si-CDs, when used as fluorescent nanoprobes, Si-CDs can rapidly and universally label dead bacteria, fungi, and mammalian cells, which can meet the needs of green fluorescent nanoprobes for specific imaging of dead cells, so as to fast discriminate live/dead cells. We believe that Si-CDs with excellent optical performance, ultrasmall particle size, and low cytotoxicity can be applied to the fields of biological imaging, optical devices, and anti-counterfeiting.