In this contribution, the synthesis of fluorescent carbon quantum dots (CQDs) by laser fragmentation is reported. To achieve it, an initial suspension of carbon glassy microparticles in polyethylene glycol 200 is irradiated using two different experimental setups, a batch and a flow jet configuration. While the batch configuration is the standard irradiation setup, the flow jet configuration is less extended and it is proposed an implementation with common laboratory material. Besides, this system ensures an improved control over the fluence and the energy delivered to the target, increasing CQDs fabrication rate by 15%. The fluorescence of the generated nanoparticles is measured obtaining an increase of the quantum yield of one order of magnitude. The achieved fluorescence together with their easy cell internalization permits their use as fluorophore. To prove it, the flow jet synthesized CQDs are used for fluorescent imaging of healthy and cancerous human cells. The required incubation time is only 10 minutes and no centrifugation or any other extra processing of the sample is needed. In addition, the fluorescence photostability is measured to be of more than 2 hours in an in vitro application, proving the viability of the generated CQDs even for labeling in applications where long image acquisition times are required.
A laser-based “green” synthesis of nanoparticles (NPs) was used to manufacture gold NPs in water. The light source is a Ti:Sapphire laser with 30 fs FWHM pulses, 800 nm mean wavelength, and 1 kHz repetition rate. The method involves two stages: (1) pulsed laser ablation in liquids and (2) photo-fragmentation (PF). Highly pure and well-dispersed NPs with a diameter of 18.5 nm that can be stored at room temperature without showing any agglomeration over a period of at least 3 months were produced without the need to use any stabilizer. Transmittance spectra, extinction coefficient, NPs agglomeration dynamics, and thermal conductivity of the nanofluids obtained were analyzed before and after being submitted to thermal cycling and compared to those obtained for commercial gold/water suspensions. Optical properties have also been investigated, showing no substantial differences for thermal applications between NPs produced by the laser ablation and PF technique and commercial NPs. Therefore, nanofluids produced by this technique can be used in thermal applications, which are foreseen for conventional nanofluids, e.g., heat transfer enhancement and solar radiation direct absorption, but offering the opportunity to produce them in situ in almost any kind of fluid without the production of any chemical waste.
Films made of Polymethylmetacrylate (PMMA) and doped with dipolar second order nonlinear optical chromophores
were studied by UV-visible spectroscopy and transmitted resonant Second Harmonic Generation technique. The
chromophores were non-centrosymmetrically oriented by a Corona poling field. The UV-visible spectra were measured
in poled films at normal incidence as function of their poling temperatures (60, 80 and 100°C) and they were analyzed in
terms of the Second Order Parameter (A2). The Second Harmonic Generation (SHG) signals in the films were measured
in-situ as function of the poling time at several incidence angles for each poling temperature. The stability of the SHG
signal was also determined, by turning off the Corona field but leaving the films at their original poling temperature. The
films were of two different kinds: amorphous and nanostructured. All the films doped simultaneously with chromophores
and surfactants showed long-range ordered nanostructures. Two kinds of surfactants were used during the synthesis of
the films: ionic and neutral, both of them induced long-range order in the structure of the PMMA, but only some of the
nanostructured films exhibited enough large SHG signals. The second order nonlinear optical response of the
nanostructured films was compared with the corresponding response of the amorphous films. The long-range order in the
films was detected by X-Ray Diffraction (XRD).
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