(Invited) Quantitative in Vitro/In Vivo Fluorescence Bioimaging with Graphene Quantum Dots

Abstract

Graphene Quantum Dots (GQDs) are novel carbon nanomaterials consisting of few layers of partially functionalized graphitic carbon. Their nanometer-scale size together with functional groups render GQDs more water soluble and biocompatible than many other nanocarbon constructs. Like many nanocarbons, GQDs possess structure-dependent optical properties, exhibiting confinement-defined fluorescence in the visible and defect-originated emission in the near-infrared (NIR). These properties give GQDs a certain advantage for applications in therapeutic tracking, imaging, analyte detection and targeted drug/gene delivery. In addition to tracing the location of therapeutic or analyte, GOD fluorescence allows for several modes of quantitative assessment within these applications. In vitro it is utilized to evaluate relative amounts of therapeutics or analytes present within the cells at a certain time period. In vivo NIR emission of the GQDs-based sensors implanted under the skin can help detect trace quantities of analyte in the body, while their NIR fluorescence in animal organs can quantify relative therapeutic uptake over time.The present work introduces novel studies and analytical tools exploring and enhancing such imaging modalities. Although GQD in vitro fluorescence microscopy imaging is often used to quantitate their (and payload) uptake and excretion, this method suffers from multiple discrepancies including the analysis of dead cells, cellular debris and non-internalized nanomaterials, and can be also time and resource-consuming. Our work aiming to circumvent these issues utilizes Artificial Intelligence (AI) approach to provide more accurate quantification of the uptake/excretion of the GQDs and their payload. In this application the AI algorithms developed in house do not only optimize the imaging, but also provide automated image analysis streamlining the assessment of a variety of GQD biomedical applications including therapeutic delivery and targeting. In vivo quantitative animal imaging with several different types of GQDs, from pristine to doped with rare earth metals for NIR fluorescence enhancement, is performed to evaluate GQD organ accumulation over time. Defect or dopant-originated NIR GQD fluorescence in the range of 900 – 1060 nm due to its high penetration depth can be observed from the organs of sedated live mice and utilized for GQD uptake tracking. NIR imaging of the excised organs allows for quantitative biodistribution assessment with further microscopic confirmation of the GQD content in organ tissue slices. Quantitative optical imaging and analysis presented in this work for GQDs can aid the further advancement of these novel nanomaterials in therapeutic delivery and analyte detection applications in vitro and in vivo.