In this work we performed a detailed investigation of the photostability of bottom-up produced carbon nanodots (CDs) prepared from citric acid and urea by solvothermal synthesis. Analytical ultracentrifugation (AUC) reveals that the CDs have a hydrodynamic diameter of o1 nm and a very narrow size distribution.In the community it is widely assumed that CDs are photo-stable. In contrast, we found that CDs exposed to UV-irradiation exhibit noteworthy fluorescence degeneration compared to freshly prepared CDs or CDs stored in the dark, indicating that fluorescence bleaching is caused by a photochemical process. We found that fluorescence intensity decay due to exposure to UV-irradiation is accelerated in the presence of oxygen and identified the surface status of CDs as the decisive factor of fluorescence bleaching of CDs.Based on a discussion on the underlying mechanisms we show how to avoid photobleaching of CDs.

We propose an effective strategy to enhance and modulate the photoluminescence (PL) of graphene quantum dots (GQDs) in the vicinity of a single silver nano-octahedron (SNO) utilizing three-dimensional finite-difference time-domain calculations. The SNO is designed to act as a multifrequency plasmonic antenna with multiple plasmon resonance modes covering multiple emission peaks of GQDs. The spectral modifications of spontaneous emission are investigated with the variations of the GQD's position and dipole moment orientation relative to the SNO. The PL colour of the GQD can be precisely adjusted between blue and green through the strong interaction with the designed antenna. The multicolour features of GQDs will also facilitate their potential applications as eco-friendly and multifunctional optical probes. The study contributes to a deeper understanding of the PL properties of GQDs near the metallic nanoparticles.

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We report a facile method of synthesizing graphene quantum dots (GQDs) with tunable emission. The as-prepared GQDs each with a uniform lateral dimension of ca. 6 nm have fine solubility and high stability. The photoluminescence mechanism is further investigated based on the surfacestructure and the photoluminescence behaviors. Based on our discussion, the green fluorescence emission can be attributed to the oxygen functional groups, which could possess broad emission bands within the π–π* gap. This work is helpful to explain the vague fluorescent mechanism of GQDs, and the reported synthetic method is useful to prepare GQDs with controllable fluorescent colors.

We synthesize Au@SiO 2 composite particles with a core-shell structure, and utilize the Au@SiO 2 nanoparticles to modulate the fluorescence emission of the graphene quantum dot (GQD) through varying the silica shell thickness. The silica shell thickness can be easily controlled by varying the coating time. After silica coating, we investigate the influence of the silica thickness on the fluorescence emission of the GQD and find that the fluorescence property of the GQD can be changed as expected by varying the thickness of the silica shell. We propose an optimized coating time for the silica shell under the interaction of fluorescence quenching and enhancement.

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Wang Wen-Shuo(王闻硕) a) , He Da-Wei(何大伟) a) † , Wang Ji-Hong(王继红) b) , Duan Jia-Hua(段嘉华) a) , Peng Hong-Shang(彭洪尚) a) , Wu Hong-Peng(吴洪鹏) a) , Fu Ming(富 鸣) a) , Wang Yong-Sheng(王永生) a) , and Zhang Xi-Qing(张希清) a) ‡

The bicuspid aortic valve (BAV) is a congenital malformation of the aortic valve with a variety of structural features. The current research on BAV mainly focuses on the systolic phase, while ignoring the diastolic hemodynamic characteristics and valve mechanics. The purpose of this study is to compare the differences in hemodynamics and mechanical properties of BAV with different phenotypes throughout the cardiac cycle by means of numerical simulation. Based on physiological anatomy, we established an idealized tricuspid aortic valve (TAV) model and six phenotypes of BAV models (including Type 0 a–p, Type 0 lat, Type 1 L–R, Type 1 N-L, Type 1 R-N, and Type 2), and simulated the dynamic changes of the aortic valve during the cardiac cycle using the fluid–structure interaction method. The morphology of the leaflets, hemodynamic parameters, flow patterns, and strain were analyzed. Compared with TAV, the cardiac output and effective orifice area of different BAV phenotypes decreased certain degree, along with the peak velocity and mean pressure difference increased both. Among all BAV models, Type 2 exhibited the worst hemodynamic performance. During the systole, obvious asymmetric flow field was observed in BAV aorta, which was related to the orientation of BAV. Higher strain was generated in diastole for BAV models. The findings of this study suggests specific differences in the hemodynamic characteristics and valve mechanics of different BAV phenotypes, including different severity of stenosis, flow patterns, and leaflet strain, which may be critical for prediction of other subsequent aortic diseases and differential treatment strategy for certain BAV phenotype.