UC Riverside

The development of patterning high-resolution microfluidic circuits onto cellulose paper in 2007 initiated widespread research into the use of the paper as a low-cost, easy-to-use alternative substrate over the glass and plastics of traditional microfluidics. Paper, as a porous hydrophilic material, naturally wicks fluid through itself, without the need to external pumps or power sources. The patterning of paper into hydrophobic and hydrophilic regions, now achievable with consumer-grade office printers, allowed the design of new 2D devices, capable of multi-analyte detection. 3D devices, made from multiple stacked layers of paper, offer even more possibilities for complex, multi-fluid routing in smaller overall device footprints. The use of patterned aerosol adhesives are investigated as an improved method of attaching multiple paper layers together rapidly and with minimal interference of interlayer fluid transport. Patterned aerosol adhesives also enable the development of nonplanar 3D devices, which represent a novel platform upon which to develop new microfluidic devices, which would otherwise be impossible to construct or function in a planar device.

Much of paper microfluidics research is focused on developing more sophisticated detection methods that provide quantitative data, instead of simple colorimetric qualitative yes/no answers. Frequently quantification is obtained by scanning the device and performing a color intensity analysis to relate a color change to concentrations of a target analyte. This technique suffers due to variations in the quality of imaging equipment and the ambient lighting conditions during image acquisition. To address this, some have proposed a distance-based lateral flow device, where the distance traveled by a colored substance is proportional to the target analyte concentration. The use of a microsphere aggregation-based sandwich assay was investigated for semi-quantitatively determining the concentration of a target ssDNA strand.