On-off-on fluorescent nanosensor for Fe3+ detection and cancer/normal cell differentiation via silicon-doped carbon quantum dots

In this study, an on-off-on fluorescent nanosensor based on carbon quantum dots (or carbon dots, CDs) was successfully fabricated for Fe3+ detection and selective imaging of cancerous cells in vitro and in vivo. The multifunctional CDs were prepared by a one-pot solvothermal treatment of glycerol and a silane molecule (N-[3-(trimethoxysilyl)propyl]ethylenediamine, DAMO). The as-prepared CDs exhibited excellent fluorescence (FL) properties and favorable biocompatibility, and could realize wash-free cell imaging both in vitro (e.g., for bacterial and fungal cells) and in vivo (e.g., for zebrafish embryos). On the other hand, the fluorescence of CDs can respond to Fe3+ selectively and sensitively, with a very low detection limit of 16 nM. Besides, detection of Fe3+ in living cells and zebrafish was also successfully realized by the CDs. Moreover, it was found that glutathione (GSH) could enhance the fluorescence of the mixed solution of CDs and Fe3+ (CDs/Fe3+), and such a property could be utilized to efficiently distinguish cancerous cells from normal ones based on the difference in the content of GSH of the two types of cells. More importantly, GSH also realized the enhanced fluorescence signals of CDs/Fe3+ in tumor site in vivo after intravenous injection, indicating the potential of CDs/Fe3+ for imaging-guided precision cancer diagnosis.