L-cysteine modified N-doped carbon quantum dots derived from peach palm (Bactris gasipaes) peels for detection of mercury ions

Establishing an effective strategy for Hg2+ determination with good sensitivity and high selectivity is of particular concern. In this work, N-doped carbon quantum dots (N-CQDs) were obtained for the first time from peels of peach palm fruit (Bactris gasipaes) through microwave-assisted one-pot synthesis. Surface N-CQDs was modified with l-cysteine (N-CQDs/CYS) by a chemical reaction (known as amide coupling) between the nitrogen-containing groups (amine group) of l-cysteine ligand and the carboxyl groups of N-CQDs. The chemical bonding was examined by Fourier Transform Infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). N-CQDs/CYS nanoparticles exhibited a quantum yield of fluorescence (ΦFL) of 25.4 %, high solubility in water, and a surface with thiol groups from l-cysteine. Mercury ions induced quenching of fluorescence of N-CQDs/CYS at low concentrations (Limit of Detection, LOD = 0.19 μM) with great sensitivity. A significant preference for Hg2+ ions was found because of the high affinity between the thiolate groups of N-CQDs/CYS and the analyte. Time-resolved fluorescence measurements were done to study the way that led to fluorescence quenching when Hg2+ ions were present, evidencing a static quenching fluorescence mechanism. The new N-CQDs/CYS material could be applied to accurately measure the concentration of Hg2+ ions in water samples in a fast and cost-effective way.