Researchers from the Indian Institute of Technology (IIT) have used mango leaves to synthesize fluorescent graphene quantum dots, and integrated those into probes for bioimaging and intracellular temperature sensing.

The unique quantum dots are reportedly biocompatible, have excellent photostability and show no cellular toxicity. To make them, the team cut mango leaves and froze them using liquid nitrogen. The frozen leaves were crushed into powder and dipped in alcohol. The extract was centrifuged and the supernatant evaporated in an evaporator and then heated in a microwave for five minutes to get a fine powder.

Using mice fibroblast cells, the team evaluated the potential of quantum dots for bioimaging and temperature-sensing applications. In mice cell in vitro studies, the graphene quantum dots were able to get into the cells easily without destroying the integrity, viability and multiplication of the cells. The quantum dots, 2-8 nanometre in size, were found to emit red luminescence when excited by UV light. “Even when the excitation wavelength was 300-500 nanometre, the emission from the quantum dots was at 680 nanometre. The quantum dots exhibited excitation-independent emission” says a team member.

The quantum dots have smaller and larger fluorescent units. When the excitation is at lower wavelength, the smaller units transfer energy to the larger units and there is red emission. And when the excitation is at higher wavelength, the red emission comes directly from the larger units, thus remaining excitation-independent.

“Since the quantum dots get into the cytoplasm of the cell, the graphene quantum dots can be used for cell cytoplasm labeling applications” explain the scientists.

The quantum dots found inside the cells showed intense florescence at 25 degree C. As the temperature rises to 45 degree C, the intensity of fluorescence tends to decrease. As a result, the researchers found up to 95% reduction in fluorescence intensity when the temperature was increased by 20 degrees C. “So quantum dots can be used for detecting temperature variation in the intracellular environment” says the team.

“Since the quantum dots emit red light, they can be used for making organic light-emitting diodes as well,” says the team.



graphene quantum dots. 2-8 nm

graphene quantum dots. 2-8 nm in size.

that means one could even make an fluorescent organic dye molecule out of graphene quantum dots?