Sweat-Based Noninvasive Skin-Patchable Urea Biosensors with Photonic Interpenetrating Polymer Network Films Integrated into PDMS Chips.

A wearable noninvasive biosensor for in situ urea detection and quantification was developed using a urease-immobilized photonic interpenetrating polymer network (IPN) film. The photonic IPN film was intertwined with solid-state cholesteric liquid crystals (CLC) and a poly(acrylic acid) (PAA) network on a flexible poly(ethylene terephthalate) substrate adhered to a poly(dimethylsiloxane) (PDMS) chip that was fabricated using an aluminum mold. The presence of urea in the chemical matrix of human sweat red-shifted the reflected color of the photonic IPN film, and quantification was achieved by observing the wavelength at the photonic band gap (λ) with a limit of detection of 0.4 mM and a linear range of 0.9-50 mM. The color changes observed in the photonic IPN film were digitalized using the CIE 1931 coordinates on a cell phone image, thereby enabling fast, direct diagnosis via a downloadable app. This novel PDMS chip can be expanded for use with other biosensors.