Highly selective and sensitive detection of calcium (II) ions in human serum using novel fluorescent carbon dots

A unique and facile biosensing system for the detection of low-concentration divalent calcium ions (Ca2+) in human serum was developed using an environmentally benign, blue-colored fluorescent multi carboxylic acid-functionalized carbon dots (CDs) that were synthesized from ethylenediaminetetraacetic acid (EDTA) via a hydrothermal process. These CDs are termed as ECDs. Our results showed that this newly developed strategy can offer an expeditious, highly sensitive, and selective detection of Ca2+ ions in human serum, with a detection limit as low as 77 pM and a potent working range of 1-10 nM. The Ca2+ ions interact with the carboxylic groups of the ECDs, could be resulting in a strong photoluminescence quenching of the ECDs via a non-radiative electron or energy transfer process. Furthermore, the detection of Ca2+ ions in human serum sample obtained using this sensing system was in good agreement with results derived from inductively coupled plasma-mass spectrometry analysis. No significant PL quenching was observed with other ionic species such as Na+, Mg2+, Fe2+, and Fe3+ owing to their monovalent nature and the fact that they typically exist in human serum at very low concentrations, which disfavors the formation of their corresponding complexes on the surface of the ECDs. (C) 2017 Elsevier B.V. All rights reserved.