We present all-dielectric gallium phosphide (GaP) nanoantennas as an e cient nanophotonic platform for surface-enhanced second harmonic generation (SHG) and uorescence (SEF), showing negligible losses in the visible range. Employing single GaP nanodisks, we observe an increase of more than three orders of magnitude in the SHG signal in comparison with the bulk. This constitutes an SHG e ciency as large as 0.0002%, which is, to the best of our knowledge, the highest yet achieved value produced by a single nano-object in the optical region. Furthermore, we show that GaP dimers with 35 nm gap can enhance up to 3600 times the uorescence emission of dyes located in the gap of the nanoantenna. This is accomplished by a uorescence lifetime reduction of, at least, 22 times, accompanied by a high intensity eld con nement in the gap region. These results open new avenues for low-loss nanophotonics in the optical regime.
We have developed an in-situ method to estimate the lateral size of exfoliated nanosheets dispersed in a liquid. Using standard liquid exfoliation and size-selection techniques, we prepared a range of dispersions of graphene, MoS 2 and WS 2 nanosheets with different mean lateral sizes. The mean nanosheet length was measured using transmission electron microscopy (TEM) to vary from ~40 nm to ~1 m. These dispersions were characterised using a standard dynamic light scattering (DLS) instrument. We found a well-defined correlation between the peak of the particle size distribution as outputted by the DLS instrument and the nanosheet length as measured by TEM. This correlation is consistent with the DLS instrument outputting the radius of the sphere with volume equal to the mean nanosheet volume. This correlation allows the mean nanosheet length to be extracted from DLS data.
Shedding light on cells: Quantum dot (QD)–gelatin nanocomposites, prepared by the synthesis of CdTe nanoparticles in the presence of gelatin, exhibit increased QD luminescence efficiencies. The nanocomposites penetrate the cell membrane and illuminate the cytoskeleton of macrophage cells (see image). Compared to the originals, the gelatin‐modified QDs display significantly lower rates of cytotoxicity and improved biocompatibility.
We have studied the photodynamic properties of novel CdTe quantum dots—methylene blue hybrid photosensitizer. Absorption spectroscopy, photoluminescence spectroscopy, and fluorescence lifetime imaging of this system reveal efficient charge transfer between nanocrystals and the methylene blue dye. Near-infrared photoluminescence measurements provide evidence for an increased efficiency of singlet oxygen production by the methylene blue dye. In vitro studies on the growth of HepG2 and HeLa cancerous cells were also performed, they point toward an improvement in the cell kill efficiency for the methylene blue-semiconductor nanocrystals hybrid system.
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