Optical glucose biosensor based on photonic interpenetrating polymer network with solid-state cholesteric liquid crystal and cationic polyelectrolyte

A patterned photonic array of dots with a photonic interpenetrating polymer network (IPN) structure consisting of intertwined photonic solid-state cholesteric liquid crystals (CLC_solid) and cationic polyelectrolyte networks was utilized for glucose detection. The photonic CLC_solid network was prepared using a reactive mesogen mixture (RMM 727, Merck) doped with the chiral dopant CB15¹, followed by ultraviolet (UV) curing and chiral dopant extraction. The networked cationic polyelectrolyte was prepared by infiltrating a monomer mixture of DMAEMA² and acrylic acid (AA) (85:15 mol%) and a crosslinker of TPGDA³ into the extracted space of the CLC_solid network, UV curing under a photomask, washing the unreacted monomers outside the dots, and immobilizing the glucose oxidase (GOx) at the AA units via a coupling reaction with EDC⁴. The prepared patterned photonic dots display a clear pH response in terms of a redshift with decreasing pH because the intertwined poly(DMAEMA) (PDMAEMA) is a typical weak cationic polyelectrolyte which protonates and expands at pH values below its pK_b. Thus, the enzymatic reaction of GOx with glucose causes a decrease in pH, expansion of the PDMAEMA, and a redshift of the reflected photonic color. The optimized photonic optical sensor shows a linear range of 0.7–12 mM with a detection limit of 0.021 mM, superior selectivity, and excellent spike test results with real blood serum. The developed photonic IPN sensor is attractive because it is cost-effective, battery-free, and allows easy naked-eye optical detection without the need for sophisticated analytical instrumentation.