A combination of acoustophoresis and thermophoresis for enriching nanoparticles

Over the past few decades, nanotechnology has seen widespread growth in biomedical applications. Recently, thermophoresis has been proposed as an efficient method to manipulate nanoparticles. However, the enrichment time can be quite long due to the associated convection flow. To address this issue, this paper proposes a novel method that combines the deployment of standing surface acoustic waves (SSAW) and temperate gradients for more efficient nanoparticle enrichment. The enrichment system consists of a microchamber sandwiched by a piezoelectrical substrate top slide, from where infrared light laser heat source and SSAW are introduced, and a sapphire bottom. The SSAW-induced thermoacoustic streaming can be properly controlled to partially cancel the effect of natural heat convection, reducing its adverse impact on thermophoresis and consequently reducing the enrichment time. A numerical model is established, which is verified against experimental observation. A parametric study is then undertaken to examine the influence of the acoustic field on the enrichment time with a laser power of 194 mW. The efficiency and suitability of the coupled system depend on the magnitude and direction of SSAW. With the optimized actuation condition, the enrichment time can be reduced by 61% compared to that of the pure thermophoretic enrichment. Finally, different laser powers are considered, ranging from 194 to 248 mW. Again, around 61% time reduction can be achieved in all the tested cases. The optimum magnitude of the acoustic waves slightly increases with the laser power. This innovative enrichment approach is thus demonstrated to be effective.