Nanoparticles (NPs) applications in energy, medicine, additive manufacturing, or catalysis require the development of synthesis techniques offering solvent and material versatility, morphology, size control, and high purity, together with industrial-scale productivities. Pulsed laser ablation in liquids (PLAL) comes close to meet these requirements; however, NP size control and further productivity increase remain a challenge. The spatial and temporal modification of the laser beam appear as an ideal approach to modify the cavitation bubble dynamics and influence NP size distribution, and to increase productivity by reducing cavitation bubble pulse shielding. Here, a (9 ± 1) wt% reduction of the characteristic NP bimodality is shown by a double pulse configuration with inter-pulse delay of 600 ps. Furthermore, synchronous double pulse PLAL with controlled inter-pulse distance is shown to modify bubble merging dynamics, resulting approximately in a factor 3 NP size increase. Finally, multi-beam PLAL is proposed as an alternative to increase inter-pulse distance and reduce cavitation bubble pulse shielding, showing a factor 4 maximum productivity increase compared to standard PLAL.
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.
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