Ultrasensitive fluorometric determination of iron(iii) and inositol hexaphosphate in cancerous and bacterial cells by using carbon dots with bright yellow fluorescence

An ON-OFF-ON dual-function fluorescent nanoprobe is described for the trace detection of ferric ions and inositol hexaphosphate (IP6) in living cells. It is based on the use of yellow-fluorescent nitrogen-doped carbon dots (YN-CDs). Highly fluorescent YN-CDs were synthesized by a hydrothermal process. They have an absolute quantum yield of 2.15% and excitation/emission peaks at 420/575 nm. Fluorescence is quenched by Fe(3+)via photo-induced electron transfer. The quenchometric assay has a 34 nM detection limit for Fe(iii). On addition of IP6 which has a high affinity for Fe3+ due to the formation of Fe-O-P bonds, fluorescence becomes gradually restored. The resulting ON-OFF-ON assays for Fe(iii) and IP6 are reliable and sensitive. IP6 can be detected at concentrations as low as 2 nM. The nanoprobe was then applied to the determination of Fe3+ and IP6 in living cells in a food matrix. Furthermore, YN-CDs exhibited excellent biocompatibility. Hence, the probe can be applied as a fluorescent ink for bioimaging, both in vitro (cancer cells and bacteria) and in vivo (nematodes and mice).