Chunyan Qiao

Strongly fluorescent graphene quantum dots (GQDs) have been prepared by one-step solvothermal method with PL quantum yield as high as 11.4%. The GQDs have high stability and can be dissolved in most polar solvents. Because of fine biocompatibility and low toxicity, GQDs are demonstrated to be excellent bioimaging agents.

Abstract The bandgap in graphene‐based materials can be tuned from 0 eV to that of benzene by changing size and/or surface chemistry, making it a rising carbon‐based fluorescent material. Here, the surface chemistry of small size graphene (graphene quantum dots, GQDs) is tuned programmably through modification or reduction and green luminescent GQDs are changed to blue luminescent GQDs. Several tools are employed to characterize the composition and morphology of resultants. More importantly, using this system, the luminescence mechanism (the competition between both the defect state emission and intrinsic state emission) is explored in detail. Experiments demonstrate that the chemical structure changes during modification or reduction suppresses non‐radiative recombination of localized electron‐hole pairs and/or enhances the integrity of surface π electron network. Therefore the intrinsic state emission plays a leading role, as opposed to defect state emission in GQDs. The results of time‐resolved measurements are consistent with the suggested PL mechanism. Up‐conversion PL of GQDs is successfully applied in near‐IR excitation for bioimaging.

Mechanical force signaling in cells has been regarded as the biological foundation of various important physiological functions. To understand the nature of these biological and physiological processes, imaging and determining the mechanical signal transduction dynamics in live cells are required. Herein, we proposed a strategy to determine mechanical force as well as its changes with single-particle dark-field spectral microscopy by using a single plasmonic nanospring as a mechanical sensor, which can transfer force-induced molecular extension/compression into spectral responses. With this robust plasmonic nanospring, we achieved the visualization of activation of localized mechanical force transduction in single live cells triggered by reactive-oxygen-species (ROS) stimulation. The successful demonstration of a biochemical ROS signal to mechanical signal conversion suggested this strategy is promising for studying mechanical force signaling and regulation in live biological systems.