Development of a Thermoresponsive Valve Membrane for Microfluiic Paper-Based Analytical Devic

Microfluidic paper-based analytical devices (μPADs) have recently attracted the attention of researchers and industry because they are small, easily fabricated, inexpensive, and require small sample volumes. However, it is difficult to simplify complex assays on such devices because there are limited means of fluid control. Therefore, in the present study we developed a thermoresponsive valve membrane by polymerizing N-isopropylacrylamide (NIPAAm) in a porous membrane. PNIPAAm is a thermoresponsive polymer; it becomes hydrophilic below, and hydrophobic above, the lower critical solution temperature (LCST; 32 °C). We used a green dye solution to investigate flow in a three-dimensionally stacked, T-shaped paper network containing the thermoresponsive valve. The valve membrane was able to prevent the passage of green dye at 25 °C (<; LCST). On the other hand, green dye was able to path through the valve membrane and 40 °C (> LCST). The result demonstrates that our thermoresponsive valve could be used in μPADs. Moreover, it has the potential to automatically enable complex immunoassays in μPADs and improve their versatility.