On-chip label-free sorting and enrichment of microplastic particles by using deterministic lateral displacement

A novel deterministic lateral displacement (DLD) method employing a pressure-driven flow for the continuous size-based separation of microplastic particles is presented in this paper. To induce the DLD effect, arrays of triangular posts were designed to enhance the sorting resolution and reduce the particles clogging. For the particles with a diameter larger than the critical diameter ($D_c$) in the DLD device, they move in bump mode with collision to microposts. While, the particles flow in zigzag mode if their sizes are below the $D_c$ value. The DLD microfluidic chip enables simplified fabrication process and shows property of label-free and high throughput. Numerical studies were conducted to discuss the $D_c$ values in the microchannel with horizontally symmetrical and asymmetrical posts, where $D_c$ was found smaller in the asymmetric horizontal flow, enabling higher separation sensitivity and resolution. Experiments were conducted to demonstrate the separation of 10 μm and 15 μm polystyrene microplastic particles, and different types of polystyrene and polyethylene microplastic particles by adjusting the flow rates. In order to achieve successful separation, the flow rates between the sheath flow and the sample solution were well matched. In this way, the proposed DLD microfluidic chip with horizontally asymmetrical triangular posts shows property of label-free, high throughput, capability to analyze microplastic particle selectively and sensitively, possibility of sorting nanoplastic particles.