Photonic Interpenetrating Polymer Network Fibers Comprising Intertwined Solid-State Cholesteric Liquid Crystal and Polyelectrolyte Networks for Sensor Applications

Uniform-sized photonic interpenetrating polymer network (IPN) fibers comprising intertwined solid-state cholesteric liquid crystal (CLC solid ) and anionic poly(acrylic acid) (PAA) or cationic poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) networks (photonic IPN PAA or IPN PDMAEMA fibers) were developed for sensor applications. IPN PAA or IPN PDMAEMA fibers with a perfect photonic structure were fabricated inside Teflon tube templates without any treatments for realizing a planar orientation in those fibers. The dominant wavelength of the photonic color from a photograph taken with a cellular phone was used to measure the photonic color change. Photonic IPN PAA fibers treated with KOH (IPN KOH fibers) were used for sensing humidity and divalent metal ions. The linear ranges for relative humidity and Ca 2+ detection were 21–92% and 0.5–3.5 mM, and their limits of detection (LODs) were 7.86% and 0.07 mM, respectively. The photonic IPN PAA (or IPN PDMAEMA ) fiber immobilized with urease (IPN PAA-urease ) (or glucose oxidase (IPN PDMAEMA-GOx )) was used for urea (or glucose) biosensor application. The photonic IPN PAA-urease (or IPN PDMAEMA-GOx ) fiber was red-shifted in response to urea (or glucose) in the linear range of 10–60 mM (or 2–16 mM) with an LOD of 2.54 mM (or 0.76 mM). These photonic IPN fibers are promising because of their easy fabrication and miniaturization, battery-free device, cost-effectiveness, and visual detection without using sophisticated analytical instruments. The developed photonic IPN fibers provide new possibilities for the widespread use of photonic sensors in cutting-edge wearable technology and beyond.