To obtain graphene-based fluorescent materials, one of the effective approaches is to convert one-dimensional (1D) graphene to 0D graphene quantum dots (GQDs), yielding an emerging nanolight with extraordinary properties due to their remarkable quantum confinement and edge effects. In this review, the state-of-the-art knowledge of GQDs is presented. The synthetic methods were summarized, with emphasis on the top-down routes which possess the advantages of abundant raw materials, large scale production and simple operation. Optical properties of GQDs are also systematically discussed ranging from the mechanism, the influencing factors to the optical tunability. The current applications are also reviewed, followed by an outlook on their future and potential development, involving the effective synthetic methods, systematic photoluminescent mechanism, bandgap engineering, in addition to the potential applications in bioimaging, sensors, etc.

Quantum dots have been used in biomedical research for imaging, diagnostics and sensing purposes. However, concerns over the cytotoxicity of their heavy metal constituents and conflicting results from in vitro and small animal toxicity studies have limited their translation towards clinical applications. Here, we show in a pilot study that rhesus macaques injected with phospholipid micelle-encapsulated CdSe/CdS/ZnS quantum dots do not exhibit evidence of toxicity. Blood and biochemical markers remained within normal ranges following treatment, and histology of major organs after 90 days showed no abnormalities. Our results show that acute toxicity of these quantum dots in vivo can be minimal. However, chemical analysis revealed that most of the initial dose of cadmium remained in the liver, spleen and kidneys after 90 days. This means that the breakdown and clearance of quantum dots is quite slow, suggesting that longer-term studies will be required to determine the ultimate fate of these heavy metals and the impact of their persistence in primates.

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SnO 2 semiconductor nanoparticles were synthesized by an ultrasonic irradiation of an aqueous solution of SnCl 4 and azodicarbonamide under ambient air. These nanoparticles are ∼3-5 nm in size, as calculated using the Debye-Scherrer formula, and as observed by TEM. The SnO 2 nanoparticles were also characterized by powder X-ray diffraction (XRD), reflection spectroscopy and FT-IR spectroscopy, transmission electron microscopy (TEM), DSC, and TGA. The band gap was calculated from reflection spectroscopy. Electrochemical tests were performed using the SnO 2 nanoparticles as the electrode's materials in nonaqueous Li salt solutions. The results showed promising reversibility, cycle life and high capacity for lithium insertion into the SnO 2 nanoparticles.

Mercaptoacetic acid (RSH)-capped CdS nanocrystals (NCs) was demonstrated to be electrochemically reduced during potential scan and react with the coreactant S2O8(2-) to generate strong electrochemiluminescence (ECL) in aqueous solution. Based on the ECL of CdS NCs, a novel label-free ECL biosensor for the detection of low-density lipoprotein (LDL) has been developed by using self-assembly and gold nanoparticle amplification techniques. The biosensor was prepared as follows: The gold nanoparticles were first assembled onto a cysteamine monolayer on the gold electrode surface. This gold nanoparticle-covered electrode was next treated with cysteine and then reacted with CdS NCs to afford a CdS NC-electrode. Finally, apoB-100 (ligand of LDL receptor) was covalently conjugated to the CdS NC-electrode. The modification procedure was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and atomic force microscopy, respectively. The resulting modified electrode was tested as ECL biosensor for LDL detection. The LDL concentration was measured through the decrease in ECL intensity resulting from the specific binding of LDL to apoB-100. The ECL peak intensity of the biosensor decreased linearly with LDL concentration in the range of 0.025-16 ng mL-1 with a detection limit of 0.006 ng mL-1. The CdS NCs not only showed high ECL intensity and good biocompatibility but also could provide more binding sites for apoB-100 loading. In addition, the gold nanoparticle amplification for protein ECL analysis was applied to the improvement of the detection sensitivity. Thus, the biosensor exhibited high sensitivity, good reproducibility, rapid response, and long-term stability.

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