Synthesis of N-doped carbon quantum dots from bio-waste lignin for selective irons detection and cellular imaging

Facile synthesis of carbon quantum dots with high fluorescence and excellent biocompatibility from plentiful and biocompatible materials still attracts much attention because of their great potential value in sensors and imaging. In this study, a highly fluorescent and super biocompatible N-doped carbon quantum dots derived from green precursor of aminated alkali lignin has been synthesized for cellular imaging. The amine-rich lignin carbon quantum dots (AL-CQDs) was firstly synthesized by introduction of secondary amine groups into lignin backbones via both Mannich and Machael addition reaction. The resulted AL-CQDs within the range of 4-10 nm exhibited excitation-dependent and pH-stable fluorescence properties and was employed for the detection of irons with a wide range from 100 nM to 1 mM and a low detection limit of 8 nM, in which the Fe³⁺ ions could be captured by the amine groups of the AL-CQDs to form an absorbent complex, resulting in a significant fluorescence quenching. Meanwhile, the AL-CQDs were successfully applied to cell imaging and intracellular irons detection benefited from low cytotoxicity and good biocompatibility. This work would shed much light on converting agricultural waste into bio-based nanomaterials and their potential applications.