30 MHz driven fluid mixing in paper-based microfluidic systems

Paper-based microfluidics have recently become a topic of interest due to the ease and low expense in fabrication, especially compared to traditional microfluidics fabrication materials, making them suitable for inexpensive diagnostics. We report a convective actuation mechanism in a simple paper-based microfluidic device using surface acoustic waves to drive mixing. Using a Y-channel structure patterned onto paper, the mixing induced by 30 MHz acoustic waves is shown to be consistent and rapid, overcoming several limitations associated with its capillary-driven passive mixing counterpart: the latter exhibits nonuniform and irreproducible mixing. Capillary-driven mixing offers only poor control, is strongly dependent on the paper's texture and fibre alignment, and permits backflow, all due to the scale of the fibres being significant in comparison to the microfluidics features. Using a novel hue-based colourimetric technique, the mixing speed and efficiency is computed. For the acoustically driven mixing ...