Photonic Interpenetrating Polymer Network Fibers Comprising Intertwined Solid-State Cholesteric Liquid Crystal and...

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 Ca²⁺ 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.