Shujun Wang

The toxicity of graphene quantum dots

Recently, there has been a rapidly expanding interest in a new nano material, graphene quantum dots, owing to its profound potential in various advanced applications. Despite its exciting application outlook, the toxicology of the material has to be well addressed before its practical use in the highly prospective areas – especially for bio-applications such as bio-sensing, bio-imaging and nanomedicine (e.g. drug delivery). This review provides a comprehensive account of the current research status regarding the toxicity of graphene quantum dots (GQDs), including raw GQDs, chemically doped GQDs and chemically functionalized GQDs. It summarises the existing tests on both in vivo and in vitro toxicity. Important topics including the uptake mechanism by cells and parameters governing the toxicity of GQDs (such as concentration, methods of synthesis, particle size, surface chemistry and chemical doping) are discussed. It also covers demonstrations on toxicity regulation of GQDs via chemical modification, as a toxicity mechanism via generation of reactive oxygen species (ROS) by some GQDs is also evident. Based on the evaluation of the current research status, possible future perspectives are also suggested.

Tailoring the edges of graphene quantum dots to establish localized π–π interactions with aromatic molecules

We report a simple route combining bottom-up and top-down strategies for the synthesis of partially ring-terminated graphene quantum dots (GQDs) employing aniline for modifying the molecular structure of GQD edges. In contrast to the GQDs synthesized without introducing ring-terminals by aniline conjugation, the photoluminescence of such partially ring-terminated GQDs can be quenched by the aromatic molecules owing to the edge-localized π–π interactions. This study provides a generalizable strategy in functionalizing GQDs towards aromatic molecule sensors, as well as important insight to the effect of edge-localized π–π interaction in perturbing the electronic structure of GQDs.

Tuning Enhancement Efficiency of Multiple Emissive Centers in Graphene Quantum Dots by Core–Shell Plasmonic Nanoparticles

Graphene quantum dots (GQDs) are emerging luminescent nanomaterials for energy, bioimaging, and optoelectronic applications. However, unlike conventional fluorophores, GQDs contain multiple emissive centers that result in a complex interaction with external electromagnetic fields. Here we utilize core-shell plasmonic nanoparticles to simultaneously enhance and modulate the photoluminescence (PL) intensities and spectral profiles of GQDs. By analyzing the spectral profiles, we show that the emissive centers are highly influenced by the proximity to the metal particles. Under optimal spacer thickness of 25 nm, the overall PL displays a four-fold enhancement compared with a pristine GQD. However, detailed lifetime measurements indicate the presence of midgap states that act as the bottleneck for further enhancement. Our results offer new perspectives for fundamental understanding and new design of functional luminescent materials (e.g., GQDs, graphene oxide, carbon dots) for imaging, sensing, and light harvesting.