Owing to their excellent photoluminescence (PL) properties, good biocompatibility, and low toxicity, graphene quantum dots (GQDs) are widely applied in bioimaging, biosensing, and so forth. However, further development of GQDs is limited by their synthetic methodology and unclear PL mechanism. Therefore, it is urgent to find efficient and universal methods for the synthesis of GQDs with high stability, controllable surface properties, and tunable PL emission wavelength. By coating with polyethyleneimine (PEI) of different molecular weights, blue-, yellow-, and red-emitting GQDs were successfully prepared. By transmission electron microscopy, atomic force microscopy, and dynamic light scattering, the characterization of size and morphology revealed that blue-emitting PEI GQDs were monocoated, like jelly beans, and red-emitting PEI GQDs were multicoated, like capsules. The amidation reaction between carboxyl and amide functional groups played an important role in the coating process, as evidenced by IR spectroscopy and theoretical calculation with density functional theory B3LYP/6-31G*. The PL-tunable GQDs exhibited an excellent chemical stability and extremely low cytotoxicity, and they had been shown to be feasible for bioimaging, making these GQDs highly attractive for a wide variety of applications, including multicolor imaging and bioanalysis.
HJS and DHJS, two near-infrared emissive
and mitochondria-targeted
therapy probes, have been designed. They exhibited photothermal &
photodynamic cytotoxicity and aggregation-induced emission (AIE) characteristics.
Interestingly, we could receive fluorescence immediately after adding
the probes without washing in 1 min. They could quickly enter cancer
cells and selectively localized to the mitochondria firstly. When
the concentration of probes was low (<5 μM), they could respond
sensitively to the mitochondrial membrane potential and would selectively
enter the mitochondria with red fluorescence. However, when the concentration
was high (≥5 μM), they would preferentially enter the
mitochondria and have the property of dual-channel fluorescence imaging
(red and near-infrared) even after 24 h. What’s more, they
increased the intracellular reactive oxygen species (ROS) levels,
decreased the mitochondrial membrane potentials, and then induced
apoptosis, which were proved by confocal imaging and flow cytometry
experiments. In addition, the results of photothermal experiment and
cytotoxicity test showed that the probes had good photothermal and
photodynamic toxicity to cancer cells. In vitro and in vivo experiments also proved the excellent near-infrared
(NIR) imaging ability, good biocompatibility and certain inhibition
of tumor growth ability of DHJS.
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