Paper-based microfluidic devices have received considerable interest due to their benefits with regards to low manufacturing costs, simplicity, and the wide scope of applications. However, limitations including sample retention in paper matrix and evaporation as well as low liquid flow rates have often been overlooked. This paper presents a paper-based capillary-driven flow system that speeds up flow rates by utilizing narrow gap geometry between two parallel surfaces separated by a spacer. The top surface is hydrophobic, while the bottom surface is a hydrophobic paper substrate with a microfluidic channel defined by a hydrophilic pathway, leaving sides of the channel open to air. The liquid flows on the hydrophilic path in the gap without spreading onto the hydrophobic regions. The closed-channel flow system showed higher spreading distances and accelerated liquid flow. An average flow rate increases of 200 and 100% were obtained for the nanoparticle-coated paperboard and the blotting papers used, respectively. Fast liquid delivery to detection zones or reaction implies rapid results from analytical devices. In addition, liquid drying and evaporation can be reduced in the proposed closed-channel system.
Keywords: capillary-driven flow; microchannel; paper-based microfluidics; parallel plates; superhydrophobic; surface flow.