Construction of composite films using carbon nanodots for blocking ultraviolet light from the Sun.

Carbon nanodots (CNDs) which demonstrate concentration-dependent emission and have a photoluminescence quantum yield of 45% were designed. Transparent CND-containing composite films (CND-films), obtained by combining the CNDs with polyvinyl alcohol in different proportions, were shown to block the UV component of sunlight. Whereas the pure PVA film could not block UV light, the ability of CND-films to block UV light could be adjusted by altering the proportion of CNDs in the film. The larger the proportion of CNDs, the greater the extent of UV blocking. CND-film containing 32 wt% CNDs completely blocked UV light (≤400 nm) from sunlight, without affecting the transmission of visible light (>800 nm). The ability of the CND-films to block the UV component of sunlight was investigated using a commercially available UV-induced color change card, which confirmed that the capacity of the CND-films to block UV light could be adjusted by altering the proportion of CNDs in the film. This study shows that CNDs with concentration-dependent long wavelength emission characteristics can be used as optical barrier units for the preparation of materials to block high-energy short wavelength light.

Seeking eye protection from biomass: Carbon dot-based optical blocking films with adjustable levels of blue light blocking.

The intensity of blue light in white light emitting diodes is typically higher than that of the green and red-light components in screen displays and lighting systems. To reduce the potential harm of in white light emitting diodes to the eyes, in this paper, we have used microcrystalline cellulose to synthesize biomass-based carbon dots (Bio-CD), which not only absorb short wavelength light to produce longer wavelength emissions, but also show concentration-dependent maximum excitation and maximum emission. The Bio-CDs were mixed with polyvinyl alcohol (PVA) to produce optical blocking films (OBF) that preferentially block blue light. OBFs have good transparency and also block blue light effectively. With OBFs containing 9.9% of Bio-CDs, the film blocked 99.6% and 98.6% of 395 nm light and 450 nm light respectively, and also blocked 93.4% and 97%, respectively, of the blue light emitted by computers and mobile phone screens. OBFs containing more than 9.9% Bio-CDs block blue light more than commercially available blue light blocking glasses. By adjusting the amount of Bio-CDs in the OBFs, it is possible to produce films with different degrees of blue light blocking to meet the requirements of different applications.

Biomass-Based Polymer Nanoparticles With Aggregation-Induced Fluorescence Emission for Cell Imaging and Detection of Fe3+ Ions.

Polymeric nanoparticles, which show aggregation-induced luminescence emission, have been successfully prepared from larch bark, a natural renewable biomass resource, in a simple, rapid ultrasonic fragmentation method. The structure, element, particle size and molecular weight distribution of larch bark extracts (LBE) were studied by FTIR, XPS, TEM, XRD and linear mode mass spectrometry, respectively. LBE was found containing large numbers of aromatic rings, displaying an average particle size of about 4.5 nm and mainly presenting tetramers proanthocyanidins. High concentration, poor solvent, low temperature and high viscosity restricted the rotation and vibration of the aromatic rings in LBE, leading to the formation of J-aggregates and enhancing the aggregation-induced fluorescence emission. LBE possessed good resistance to photobleaching under ultraviolet light (200 mW/m2). Cytotoxicity experiments for 24 h and flow cytometry experiments for 3 days proved that even the concentrations of LBE as high as 1 mg/mL displayed non-toxic to MG-63 cells. Therefore, LBE could be employed for MG-63 cell imaging, with similar nuclear staining to the DAPI. The effects of different metal ions on the fluorescence emission intensity of LBE were analyzed and exhibited that Fe3+ owned obvious fluorescence quenching effect on LBE, while other metal ions possessed little or weak effect. Furthermore, the limit of detection (LOD) of Fe3+ was evaluated as 0.17 µM.

Preparation of Biomass-Based Carbon Dots with Aggregation Luminescence Enhancement from Hydrogenated Rosin for Biological Imaging and Detection of Fe3.

Fluorescent carbon dots (CDs) have numerous important applications, but enhancing the fluorescence emission and overcoming fluorescence quenching are still big challenges. Here, fluorescence-enhanced carbon dots (named hr-CDs) were prepared from sustainable hydrogenated rosin, using a simple hydrothermal method in a water solvent. The hr-CDs were mainly composed of graphitized carbon cores with surface functional groups. With the increase in the concentration to hr-CDs aqueous solutions, the distance between the carbon cores decreased, which resulted in the formation of J aggregates and the enhanced blue fluorescence emission. Even in the solid state, the hr-CDs show fluorescence emission because the surface functional groups could prevent π-π stacking interactions between the carbon cores. The hr-CDs show excellent resistance to photobleaching under intense ultraviolet light (200 mW/cm2). Vibrations and rotations of graphitized carbon core are restricted by low temperature and high viscosity, leading to increased radiative transition and thus increase in fluorescence intensity. The pH value in the range of 3.99-9.87 and anions have little effect on the fluorescence emission of hr-CDs. The fluorescence emission of the hr-CDs was selectively quenched by Fe3+ and can thus be used to detect Fe3+. The hr-CDs also have good biocompatibility and show the same ability in cell nuclear staining as 4',6-diamidino-2-phenylindole (DAPI).