Sequential on-off-on detection of Fe²⁺ and enantiomeric l-lysine with logic gate operation based on fluorescent carbon dots derived from a zinc-amine complex

Almost all types of proteins in biology are composed of L-amino acids, and very few contain D-amino acids. Therefore, chiral recognition, especially for the detection of L-amino acids, is of great importance. In this work, luminescent zinc-doped carbon dots (Zn-CDs) were successfully synthesized through a one-step hydrothermal method using [Zn(EDA)(3)]Cl-2 (EDA = ethylenediamine) complex as a precursor, exhibiting superior water stability, low cytotoxicity and good photobleaching stability. It can be used as an "on-off-on" fluorescence probe in aqueous solution to sequentially detect Fe2+ ions and enantiomeric L-Lysine (L-Lys) molecules with the corresponding limit of detection (LOD) of 0.092 and 0.204 mu M, respectively. Also, the sequential on-off-on fluorescent changes of Zn-CDs upon the addition of Fe2+ and L-Lys can be applied in living cell imaging, as observed by the contrast of images in confocal microscopy. In addition, two distinct multi-input molecular logic gates, involving distinguishing the effect of L-Lys and D-Lys on the fluorescence of Zn-CDs, and the regulation of fluorescence quenching and recovery of Zn-CDs by Fe2+ ions and L-Lys are established. The Zn-CDs also exhibits a linearly temperature-dependent fluorescence performance with high temperature sensitivity (S-r) of 1.10% degrees C-1 in 10-90 degrees C, demonstrating its great potential for biological temperature sensing applications. This work provides a new strategy for exploring novel metal-doped carbon dots with outstanding biocompatibility and multifunctionality in biological applications.