Development of a turn-on graphene quantum dot-based fluorescent probe for sensing of pyrene in water

Polycyclic aromatic hydrocarbons (PAHs) are potentially harmful pollutants that are emitted into the environment from a range of sources largely due to incomplete combustion. The potential toxicity and carcinogenic effects of these compounds warrants the development of rapid and cost-effective methods for their detection. This work reports on the synthesis and use of graphene quantum dots (GQDs) as rapid fluorescence sensors for detecting PAHs in water. The GQDs were prepared from two sources, i.e. graphene oxide (GO) and citric acid (CA) - denoted GO-GQDs and CA-GQDs, respectively. Structural and optical properties of the GQDs were studied using TEM, Raman, and fluorescence and UV-vis spectroscopy. The GQDs were then applied for detection of pyrene in environmental water samples based on a "turn-off-on" mechanism where ferric ions were used for turn-off and pyrene for turn-on of fluorescence emission. The fluorescence intensity of both GQDs was switched on linearly within the 2-10 × 10^-6 mol L^-1 range and the limits of detection were found to be 0.325 × 10^-6 mol L^-1 and 0.242 × 10^-6 mol L^-1 for GO-GQDs and CA-GQDs, respectively. Finally, the potential application of the sensor for environmental water samples was investigated using lake water and satisfactory recoveries (97-107%) were obtained. The promising results from this work demonstrate the feasibility of pursuing cheaper and greener environmental monitoring techniques.