Improvement of selectivity via the surface modification of carbon nanodots towards the quantitative detection of mercury ions

Highly fluorescent carbon nanodots have been a promising fluorophore for analytical, pharmaceutical, and environmental analysis due to facile preparation, biocompatibility, tunability, and low-cost precursors. Selectivity improvements towards an environmentally interesting analyte is challenging in analytical chemistry. Here, surface modification using mixed solvents was used to prepare fluorescent carbon dots (CDs) as a selective fluorophore to Mercury ions (Hg2+) in the presences of other cations and anions. The solvothermal method was used for fabrication of 4-6 nm of CDs using Xylose as a carbon precursor and ethanol-H2O as a mixed solvent. Optical, morphological, and surface characterizations were conducted thoroughly. The fluorescence emission of CDs was selectively quenched after addition of mercury ions, and restored via addition of cysteine. The CDs was used successfully for quantitative detection of Hg2+ ions free from interferences. The fabricated nanoprobe exhibited a good linearity range 50–800 nM (R2= 0.9921) and a low detection limit down to 10 nM for Hg2+ was calculated. The selectivity experiments show that the fluorescent probe is specific for Hg2+ even with presence of interferences. The CDs were stable under rigorous conditions, such as extreme ionic strength, low and high pHs. Additionally, CDs were photo and thermo-stable, which make the CDs a promising fluorophore to fabricate rugged and robust nanoprobe for Hg2+ detection. Hg2+ ions in tap and wastewater were determined quantitatively with statistically good spike recoveries and standard deviations.