Human fingernails as an intriguing precursor for the synthesis of nitrogen and sulfur-doped carbon dots with strong fluorescent properties: Analytical and bioimaging applications

In this study, we describe the synthesis of N,S co-doped bright carbon dots (CDs) from human fingernails via a simple microwave irradiation procedure. Human fingernails are utilized to prepare a new kind of fluorescent CDs after sulfuric acid-enhanced microwave treatment, which show good stability in aqueous solutions, high quantum yield as well as remarkable features for fluorescence quenching-based detection and cell imaging. The procedure followed for the synthesis is very fast and energy-efficient, enabling the low-cost production of CDs with distinctive properties. The as-synthesized CDs can be used as a selective, efficient and sensitive fluorescent probe for the detection of sunset yellow in food products. Ultra-low limit of detection (0.1 nM), linear response between 0.3 and 43.4 nM and splendid reproducibility for the fluorescence-based detection of sunset yellow are the highlights of the developed analytical method. The interaction mechanism between CDs and sunset yellow is associated both with inner filter effect and static quenching. Furthermore, the produced CDs do not affect cell viability, rendering them suitable for bioimaging purposes. To the best of our knowledge, this is the first time that human fingernails, a natural source of high abundance, is used as raw material for synthetic, probing and bioimaging purposes, after microwave-assisted treatment, in the presence of sulfuric acid. (C) 2018 Elsevier B.V. All rights reserved.