Synthesis of Graphene Quantum Dots Towards Sensing and Biomedical Applications

A. Ananthanarayanan, P. Chen
Nanyang Technological University,
Singapore

Keywords: fluorescence, graphene quantum dots, bio-imaging, sensing

Summary:

Graphene Quantum Dots (GQDs) are a new class of emerging 0-dimensional materials that show immense potential due to their unique physical and chemical properties. GQDs are basically small sheets of graphene mostly less than 30 nm in lateral size and few layer thickness. Their properties such as bio-compatibility, photostability, water-solubility and organic framework make them superior fluorophores for sensing and biomedical applications. GQDs can be synthesized from large graphite-like precursors by top-down approaches or from small molecular precursors by bottom-up approaches. Synthesis of GQDs with tunable properties is an area of interest for specific applications We have developed a unique and rapid synthesis strategy for the production of high-quality GQDs by electrochemical exfoliation of 3-dimensional CVD-grown graphene foam electrode using ionic liquid (1-butyl-3-methyl imidazolium hexafluorophosphate) as the electrolyte.The GQDs have a average lateral size of 3nm and exhibit blue fluorescence with a emission wavelength centered around 440nm. The as-obtained GQDs were used as a fluorescent turn-off sensor for the ferric ions in solution. The GQDs show high specificity towards ferric ions. We have also demonstrated a simple strategy for the synthesis of nitrogen and phosphorous co-doped GQDs from a single biomolecule precursor (adenosine triphosphate - ATP). Such ATP-GQDs exhibit high fluorescence quantum yield, strong two-photon upconversion, small molecular weight, high photo-stability, and good bio-compatibility. These GQDs have numerous carboxyl groups on the edges and can be easily conjugated with protein molecules. As a proof-of-concept demonstration, transferrin conjugated ATP-GQDs have been used for in-vitro cell imaging and real-time tracking of transferrin receptors in live cells.