Investigation of inertial focusing of micro- and nanoparticles in spiral microchannels using computational fluid dynamics

Inertial microfluidics utilize hydrodynamic forces for particle manipulation and require precise trajectory estimation for efficiency. This study examines parameters affecting micro- and nanoparticle inertial focusing in microchannels by introducing a novel sunflower geometry through asymmetric serpentine segments. This design enhances inertial focusing and particle separation through the Dean effect and continuous acceleration modulation, bolstering operational efficiency. Dynamic variations in lift (F_L) and drag forces (F_D) within the sunflower geometry augment their ratio, improving particle separation. Asymmetric serpentine attribute enhances lift force by adapting the coefficients (G₁ and G₂) along the channel and amplifies the net lift force. The varying F_L in different sunflower zones concentrates particles of different sizes, while the channel curvature influences F_D. While the traditional spiral microchannel only provides global forces due to its radius of curvature, the sunflower microchannel gives rise to the superposition of local forces induced by the expanding and narrowing changing of the serpentine shape and the global forces caused by the spiral shape. The study also examines the differences between local and global force effects on particle focusing. Ultimately, a passive separation of 500 nm particle is achieved by collecting the nanoparticle on the inner surface, while 1 μm particle locates at the central axis and 3.3 μm particle clusters on the outer surface. The significance of the study is that the effective passive particle separation could be managed even for sub micrometer particles without any auxiliary external forces but with inertial forces thanks to the novel sunflower microchannel design.