Ultra-low-cost 'paper-and-pencil' device for electrically controlled micromixing of analytes

We demonstrate here a frugal, printing-based fabrication methodology for paper channels, in an effort towards developing an inexpensive micromixing device. The proposed fabrication methodology utilizes the normal ink-jet cartridge ink to create the barriers for the paper channels, without involving any additional complex materials or intermediary ink modification steps. We show through experimental observations, and pertinent scaling analysis, that the electrokinetic effects, along with the capillary and viscous forces, play a significant role in enhancing the liquid transport rate through such a paper channel under an applied electrical potential, in comparison with that observed due to natural imbibition. Thereafter, we delineate the modality of active electrical control of mixing of two liquids in such a printed 'zigzag' 'paper-and-pencil' device, by exploiting the interplay between the electrohydrodynamic flows stemming from the electrokinetic phenomena and the specific channel geometry. The electrokinetically mediated flow of the liquid samples through the 'zigzag' paper channel can be judiciously controlled to either appreciably enhance the mixing characteristics or artificially maintain the segregation of the liquid streams by overriding the inherent wicking action-driven mixing within the paper matrix. Hence, the present endeavour will usher in a new generation of paper microfluidic platforms for micromixing, with enhanced production feasibility, controllability, functioning efficiency, and multiplexing capability.