Valine-derived carbon dots with colour-tunable fluorescence for the detection of Hg2+ with high sensitivity and selectivity

Hg2+ is one of the most ubiquitous pollutants in the environment and is a danger to human health. There is a need for a simple highly sensitive method of for the detection of aqueous Hg2+. Carbon dots (CDs) have attracted widespread attention due to their potential application in bioimaging, chemisensors and photocatalyst design. We have now developed a simple and efficient method for the preparation of P-doped carbon dots (CDs) with tunable fluorescence, using L-valine as the carbon source and H3PO4 (85%) as oxidant. The fluorescence of CDs can be tuned from green (CDs-1) to yellow (CDs-2) by simply controlling the reaction time at a relatively mild temperature (90 degrees C). The CDs obtained exhibit bright photoluminescence with quantum yield (QY) up to 44.8% for CDs-1 and 31% for CDs-2, together with excellent biocompatibility and water solubility. pH and NaCl solution had no significant effect on the fluorescence intensity of CDs-1. More importantly, the green CDs show high sensitivity and selectivity in the detection of Hg2+. Two different fluorescence quenching modes have been established, the lower limit of detection (LOD) being about 1.51 nM.