Engineering Graphene Quantum Dots for Bioapplications prof. Anton V. Naumov

Engineering Graphene Quantum Dots for Bioapplications
Anton V. Naumov, Texas Christian University, Fort Worth, TX

Graphene quantum dots (GQDs) are zero-dimensional nanomaterials characterized by their remarkable properties. They range from pristine graphene-based GQDs to highly functionalized and even doped nanostructures all, however, possessing some form of graphitic lattice. GQD structure significantly influences their electronic and optical properties, which are pivotal for various applications in nanoscale electronics, biosensing, and biomedical imaging. Major synthetic approaches rendering different GQD morphologies include either bottom-up synthesis from carbonaceous molecular precursors or top-down scission of larger graphitic materials such as reduced graphene oxide into nanoscale GQDs. Microwave-assisted bottom-up hydrothermal synthesis utilized in our work allows doping GQDs to achieve application-specific characteristics. To date, over 30 different precursors and dopants are used in our work to generate GQDs that enable imaging, sensing and drug transport applications. Major electronic transitions of synthesized GQDs can arise from quantum-confined graphitic islands encircled by functional groups or dopants resulting in bright (up to 63% quantum yield) fluorescence in the visible. Electronic confinement at the defects/functional groups modeled via ground state Hartree-Fock calculations is deemed responsible for transitions in the near-infrared at 800 - 1050 nm observed in some GQD types. Doping GQDs with rare earth metals during synthetic process can also generate near-infrared-emissive structures with well-defined spectral signatures arising from atomic transitions of rare-earth dopants. GQD near-infrared fluorescence allows for a variety of bioimaging applications due to high penetration depth and low scattering of near-infrared light in biological tissues. Furthermore their substantial biocompatibility and water solubility render GQDs suitable for in vivo studies. Defect and dopant-originated near-infrared GQD fluorescence is observed from the organs of sedated live mice and utilized for tracking GQD uptake. Imaging excised organs further allows for quantitative biodistribution assessment. Other imaging modalities explored for these GQDs involve ultrasound and MRI contrast enhancement, as well as in vitro therapeutic tracking. Sensing applications of GQDs developed in our work include UV photodetection, in vitro nanothermometry and detection of cancer-generated genes for early diagnosis. GQDs also facilitate drug and gene delivery for cancer therapeutics including the transport of conventional chemotherapies, gene-silencing therapeutics and CRISPR Cas9 gene editing complexes. With a variety of advantageous structure-defined properties engineered through the variation of their synthetic process, GQDs show promising potential in the field of nano-biotechnology.