In-situ generation and shrinkage of monodisperse water-in-oil emulsion for femtoliter compartmentalization using capillary traps

A novel, facile and effective microfluidic approach to achieve monodisperse femtoliter (fL, 10^-15L) water-in-oil (W/O) droplet array is proposed for constructing artificial cell-sized micro reactors. By combining the controlled diffusion of water into oil and capillary-based 2D micro trap array (capillary traps), in-situ generation and 1000-fold volume shrinkage down to ~4 fL have been achieved for monodisperse W/O array. With improved 3D trap array, high-density and well-aligned fL W/O droplet array with good long-time stability and coefficient of variation (CV) smaller than 5% has also been demonstrated. This approach also enables dynamically tuning of droplet sizes and solution concentration useful for many applications.