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

Abstract

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]Cl₂ (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 μM, 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% °C⁻¹ in 10–90 °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.