Ioannis H. Karampelas

Analysis of pulsed laser plasmon-assisted photothermal heating and bubble generation at the nanoscale

A study is presented of photothermal effects associated with nanosecond-pulsed laser-illuminated subwavelength metallic nanoparticles in aqueous solutions. Computational electromagnetic and fluid analysis are used to model fundamental aspects of the photothermal process taking into account energy conversion within the nanoparticle at plasmon resonance, heat transfer to the fluid, homogeneous bubble nucleation, and the dynamic behaviour of the bubble and surrounding fluid. Various nanoparticle geometries are modelled including spheres, nanorods and tori. The analysis demonstrates that the laser intensity and pulse duration can be tuned to achieve controllable bubble generation without exceeding the melting temperature of the particle. The analysis also shows that the particle geometry can be tuned to optimize photothermal energy conversion for bubble generation at wavelengths that span the UV to NIR spectrum. Multiparticle systems are studied and a cooperative heating effect is demonstrated for particles that are within a few radii of each other. This provides more robust bubble generation using substantially reduced laser energy as compared to single-particle systems. The modelling approach is discussed in detail and should be of considerable use in the development of new photothermal applications.

Computational Analysis of a Two-Phase Continuous-Flow Magnetophoretic Microsystem for Particle Separation from Biological Fluids

Abstract In recent years, there has been growing interest in the use of functionalized magnetic beads for biomedical applications due to the outstanding characteristics of these materials. Furthermore, the recent development of microfluidics has enabled the continuous capture of malignant cells or toxins from biofluids for either analysis or treatment. However, the optimization of these processes has been relatively less studied and rational design is often lacking because of the complexity associated to their mathematical description. In this work, the separation of magnetic beads from flowing blood streams inside a multiphase system is analyzed through CFD techniques. The numerical model introduces a coupled magnetic and fluidic analysis that describes the bead trajectories under magnetic gradients generated by permanent magnets. A key feature of this work is that we studied for the first time the interaction between two fluids flowing simultaneously in the device while taking into account the effects of particle-fluid interactions in the flow field. Magnetic and fluidic forces on the particles are studied and optimized through a dimensionless number J. The results show that complete particle separation avoiding any mixing or perturbation of the fluids can be achieved for a certain range of the J number.