Dual-crosslinked zwitterionic hydrogel: a facile platform of wearable colorimetric urea sensors

Zwitterionic hydrogel based on a dual-crosslinked network of pluronic F-127 dimethacrylate (PLU-DMA) and a terpolymer, poly(sulfobetaine methacrylate)-co-methacrylic acid-co-N-methacryloyloxyethyl tyrosine methylester) (PSBMM) was prepared and successfully applied as an enzyme-based colorimetric sensor of urea on diaper. The prepared hydrogel possessed good mechanical property while preserving its swelling capability. The urease-incorporated hydrogel exhibited a vivid color change from yellow to orange and red, enabling semi-qualitative detection of urea via naked eye in a linear range of 0-0.7 M covering a cut-off value of 0.3 M, which allow for distinguishing between the chronic kidney-prone patients from the normal individuals. The hydrogel was found to be non-toxic and demonstrated effective enzyme preservation by maintaining more than 80% of urease activity up to 14 days. This hydrogel-based urea sensor was also validated by laser desorption ionization mass spectrometry (LDI-MS) with satisfactory results. This platform demonstrated its potential integration on diaper for real-time screening of urea in the point-of-care diagnostics of chronic kidney disease (CKD).