(Invited) Carbon Dots – from Imaging to Green Energy Applications

Abstract

In recent years, nanomaterials, defined as materials < 100 nm in a single dimension, have garnered significant interest for the development of novel applications in the physical and life sciences. This is especially true for luminescent nanoparticles, which have been investigated for the development of sensors, imaging/diagnostic probes, display and solar cell applications. Recently, a relatively new class of luminescent nanomaterials, namely carbon dots, has come to light. Carbon dots, sometimes known as carbongenic dots, are carbon, oxygen, nitrogen and hydrogen containing materials with the first two elements typically accounting for ~90% of their elemental composition. Moreover, they are typically water dispersible and can be prepared from an abundant number of inexpensive sources including small molecules such as citric acid, amino acids and sugars. While they are small in size (typically 1-10 nm), they can offer a high quantum yield of emission, a process that is controlled through passivation of the surface with an organic reagent. Of particular interest are their optical properties, which can be tailored via careful selection of the starting precursors and the desired synthesis route resulting in the ability to generate fluorescence from the blue to the near infrared regions of the spectrum. In addition to their versatile optical properties, these carbon dots are generally known to have low cytotoxicity and good biocompatibility. Combined with their small size and versatile optical properties, developing carbon dots as a nanoplatform can be achieved as they lend themselves for integration in a myriad of applications most notably in bio-imaging and sensing. Our work focuses on achieving a fundamental understanding of the synthesis of carbon dots in order to control their size and achieve homogenous surface chemistry and optical properties. As they are fluorescent, we have investigated their development as bimodal imaging probes and exploited their temperature and pH dependent optical properties in order develop novel intracellular temperature and pH sensors. We can also endow them with chiral properties during synthesis opening up novel avenues for chiral sensing and antimicrobial applications. Finally, in recent developments, we have exploited their physico-chemical properties in green energy applications focusing on the production of biofuels.