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 (IPNPAA/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 IPNPAA layer of the circularly programmed IPNPAA/PET bilayer actuator film (BAF). The urea in human sweat altered the diameter of the circular urease-immobilised IPNPAA/PET (IPNurease/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 IPNurease/PET BAF exhibited a high selectivity toward urea and excellent spike-test results with real human sweat. This novel circular IPNurease/PET BAF is promising because it is battery-free, cost-effective, and enables visual detection without sophisticated instruments. Further, the application of these IPNPAA/PET BAFs can be easily expanded to other biosensors by immobilising other receptors in the IPN.