Design, fabrication and characterization of Si-based capillary-driven microfluidic devices

Capillary-driven microfluidic devices have a great potential for the point-of-care testing systems based on the advantages of self-pumping, low reagent usage and rapid detection. Here, the study presents a lidless Si-based capillary-driven microfluidic device, comprising two inlets for sample and buffer loading, a snake-shaped microchannel (120/0.05/0.025 mm in length/width/depth) as a flow resistor, a micropillar array (25/5/8 μm in height/diameter/pitch) as a capillary pump and a vent. It was fabricated with lithographic technique in combination with deep Si etch technique. A simple and stable surface hydrophilisation modification method was demonstrated on the device by forming a self-assembly monolayer through Cu-catalysed azide-alkyne cycloaddition reaction. The surface modified device allowed controllable autonomous capillary flow delivery with a contact angle of around 40° stabilised for at least 90 days. The design of two inlets with one common long snake-shaped microchannel provided the sequential capillary flow generation and propagation with controlled flow rate and propagation distance, while the micropillar array with a high aspect ratio of 5 was considered as an effective capillary pump. Based on the obtained results, the proposed device makes possible for the on-chip biosensing applications as a part of integrated point-of-care testing systems.