Expanding channels enhanced diffractive SAW actuated particle enrichment in vacuum-sealed microfluidic channels

Diffractive surface acoustic wave (SAW) methods have recently emerged as a promising approach for bioparticle manipulation and enrichment, with advantages in flexibility and ease of alignment compared to standing-wave SAW based micromanipulation. Here we demonstrate a diffraction-based focusing approach based on an expanding channel that multiplicatively improves enrichment efficiency. Uniquely, this permits the generation of particle enrichment across several acoustic wavelengths, where particles are first focussed along channel walls, with the cross-section of the flow subsequently being arbitrarily expanded. We numerically and experimentally validate the generated pressure fields across two expanding channel geometries with comparison to a uniform channel cross-section. We further integrate a vacuum seal to improve device usability and allow for comparison of multiple designs using a single transducer. Quantitative analysis of particle enrichment was performed for each device, with expanded channels demonstrating enrichment factors and flow rates several times that of constant width designs. These advancements in enrichment through expanding channel diffractive acoustic methods hold significant promise for various applications in biomedical research, including enhanced diagnostics and therapeutics development.