Three-dimensional microfluidic devices fabricated in layered paper and tape
Andres W. Martinez, Scott T. Phillips, and George M. Whitesides
Soft Matter Keywords
Capillary Force. Microfluidics
This article describes a method for fabricating 3D microfluidic devices by stacking layers of patterned paper and double-sided adhesive tape. Paper-based 3D microfluidic devices have capabilities in microfluidics that are difficult to achieve using conventional open-channel microsystems made from glass or polymers. In particular, 3D paper-based devices wick fluids and distribute microliter volumes of samples from single inlet points into arrays of detection zones (with numbers up to thousands). This capability makes it possible to carry out a range of new analytical protocols simply and inexpensively (all on a piece of paper) without external pumps. We demonstrate a prototype 3D device that tests 4 different samples for up to 4 different analytes and displays the results of the assays in a side-by-side configuration for easy comparison. Three-dimensional paper-based microfluidic devices are especially appropriate for use in distributed healthcare in the developing world and in environmental monitoring and water analysis.
The authors here use SU8 photoresist (hydrophobic) to pattern paper with microchannels (basketweave pattern for example). A layer of tape cut with punched holes was then placed on top of the patterned paper. The holes were then filled cellulose paste in order to fill the voids created between adjacent paper layers by the tape's thickness. This process could be repeated many times over. The fluid is transported through wicking action between the paper and fluid. The cellulose in the tape's holes provide the method for vertical fluid flow, a cavity would simply fill with water and remain stagnant with surface tension. A filling with cellulose paste would allow water to wick through this area (presumably assisted by gravity)
The figure to the left shows a sample 3-dimensional device that utilizes a basket weave pattern to simultaneously multiple streams that do not mix. In this particular device, the fluid requires about 5 min. to fully travel through the device. The materials for this particular device costs about $0.03US. To illustrate the ability to flow differing streams in three dimensions with high fidelity, the authors various arrays that can be created with this method (as denoted by the different colors).
The authors emphasize that this new technique can be a boon to the developing world. It is potentially a means of cheaply doing medical or other chemical detection with limited technology. The authors demonstrate that each detection zone can be designed to be visible by eye, or with a camera phone. Additionally the authors demonstrate assays of glucose and protein to demonstrate the technique's applicability.
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