pH-responsive circular bilayer biosensor based on the actuation of an interpenetrating polymer network comprising crosslinked nematic liquid crystals and poly(Acrylic Acid)

In this study, a sweat-based biosensor was developed for the detection of urea using a bilayer film consisting of an interpenetrating polymer network (IPN) as the top layer and a flexible poly(ethylene terephthalate) (PET) layer as the bottom layer (IPN_PAA/PET). The top IPN layer had intertwined solid-state nematic liquid crystals and poly(acrylic acid) (PAA) networks. Urease was immobilised at the PAA network of the IPN_PAA layer of the circularly programmed IPN_PAA/PET bilayer actuator film (BAF). The urea in human sweat altered the diameter of the circular urease-immobilised IPN_PAA/PET (IPN_urease/PET) BAF, and was quantified by measuring the diameter using a ruler; the limit of detection was 13.2 mM and linear range was 30–60 mM. The developed circular IPN_urease/PET BAF exhibited a high selectivity toward urea and excellent spike-test results with real human sweat. This novel circular IPN_urease/PET BAF is promising because it is battery-free, cost-effective, and enables visual detection without sophisticated instruments. Further, the application of these IPN_PAA/PET BAFs can be easily expanded to other biosensors by immobilising other receptors in the IPN.