Anal. Chem. 86, 8090–8097 (2014)

Paper-based assays are advantageous because they are inexpensive and can be easily fabricated and disposed of. They are also compatible with biological samples. There are many ways to concentrate and transport the analyte in these assays during paper wetting, but most of these methods depend on passive capillary action. This means that it is generally not possible to further manipulate the analyte after wetting. David Sinton and colleagues at the University of Toronto and University of Ontario Institute of Technology now show that by incorporating a nanoporous membrane and applying ion concentration polarization (ICP), it is possible to concentrate and transport analytes in fully wet paper-based assays.

The researchers developed two classes of device. The first one is an external stamp-like device consisting of an assembly between a silicone rubber layer with an embedded nanoporous membrane and a poly(methyl methacrylate) layer containing buffer reservoirs. To function, the external device is placed on the paper-based assay, the reservoirs are filled with buffer and voltage is applied. ICP occurs at the interface of the nanoporous membrane and the paper. In the second device, the nanoporous material is patterned directly on the paper and acts as a hydrophobic barrier that defines the reservoirs and channels, and forms the micro/nano interface required for ICP. The researchers found that the external device efficiently concentrated and transported dyes directionally over centimetre distances. When used to concentrate proteins and dyes, the second device improved the limit of detection of the paper-based assay.