Facile Preparation of Fluorescent Carbon Dots from Glutathione and l-Tryptophan for Sensitive and Selective Off/On Detection of Fe3+ Ions in Serum and Their Bioimaging Application

In the past decade, carbon dots (CDs) have attracted considerable attention due to their excellent properties such as low toxicity, good biocompatibility, good fluorescence imaging, etc. Here, glutathione and l-tryptophan were used as carbon sources to hydrothermally synthesize CDs for sensitive and selective off/on detection of Fe3+ ions. The CDs are spherical nanoparticles with an average particle size of 3.8 nm and the presence of organic groups such as hydroxyl, carboxyl, sulfhydryl, and amino groups on their surface. The experiment results display that Fe3+ ions can be selectively and sensitively detected by quenching the fluorescence of CDs. Moreover, the fluorescence of the CDs+Fe3+ system can be restored after adding ascorbic acid. Thus, an off/on fluorescent probe for the determination of Fe3+ can be formed using the as-synthesized CDs solution. The CDs show a good linear range of 0-13.89 mM and a 0.0331 μM limit of detection for Fe3+, and the most probable mechanism concluded from ultraviolet-visible spectroscopy, electrospray ionization-mass spectrometry, and fluorescence spectrophotometry is a mixed static and dynamic quenching. Furthermore, the cytotoxicity experiment results show that CDs have low toxicity and can be used for intracellular imaging.