Rapid vacuum-driven monolayer assembly of microparticles on the surface of perforated microfluidic devices

On the cusp of a miniaturized device era, a number of promising methods have been developed to attain large-scale assemblies of micro- and nanoparticles. In this study, a novel method is proposed to firmly capture dispersed microparticles of nominal sizes of 10 μm on a two-dimensional array (1.0 × 1.0 mm²) of through-pores on a surface. This is obtained by dispensing a droplet of the particle dispersion on the pores, which drains by applying a vacuum-driven force at the backside of the pores. The assembled particles are captured on the surface in a reversible way, making them available for direct manipulation and inspection, or subsequent transfer of the particles to a second surface. The relevant process parameters dispersant concentration, dispersant type, particle properties, and pitch distance d, are optimized to obtain (near-)perfect ordered particle arrays. Furthermore, to significantly improve the quality of the particle assembly, washing steps are added to remove excess particles from the surface. Silica or polystyrene (PS) particle assemblies with an error ratio (ER) as low as 0.2% are obtained, demonstrating the universality of the proposed method. For the smallest pitch, d = 1.25 μm, even with optimal process parameters, higher ER-values (=1.1%) are obtained.