Printed Thin Films with Controlled Porosity as Lateral Flow Media

Traditional materials for lateral flow devices (cellulose, nitrocellulose) are typically produced in large batches with relatively thick membranes and a uniform pore size, making it challenging to develop devices with variable flow rates. With a view to the development of easily manufactured lateral flow media with variable porosity and flow rates, we investigated the ability to produce a fully printed porous media based on colloidal, precipitated calcium carbonate (PCC) dispersions containing latex binders. PCC dispersions with varying particle sizes were printed onto glass surfaces, and it was observed that flow rates could be controlled by varying particle size. On the basis of this finding, a device with three zones, having distinctly different porosities and wicking behaviors, was printed with three calcium carbonate inks in a single printing operation. The printed media were ∼10% the thickness of paper or nitrocellulose membranes, with lower porosities and wicking rates. We demonstrate that such PCC materials can adsorb enzymes such as alkaline phosphatase (ALP) with retention of activity, and show that a colorimetric ALP reaction giving a colored precipitate generated strong color signals on the printed PCC lateral flow media.