Label-free 2D colloidal photonic crystal hydrogel biosensor for urea and urease inhibitor

Abstract

A label-free urease coupled colloidal crystal hydrogel (UCCH) biosensor for the visual monitor of urea and urease inhibitor phenyl phosphorodiamidate (PPD) was developed by embedding a regular 2D polystyrene array in the surface of the urease functionalized hydrogel. In the presence of urea, ammonium and bicarbonate ions are produced owing to the enzymatic reaction. These ions reduce the electrostatic repulsion between the carboxylates of hydrogel backbone, which shrinks the UCCH volume and leads to an evident blue-shift in the diffraction wavelength. The hydrolysis of urea can be hindered when the urease inhibitor PPD is introduced in the solution along with urea, and a decrease in the blue-shift of the diffraction wavelength occurs. The monitors of urea and PPD are also realized by measuring the diameter of Debye diffraction ring, and the detection limits for urea and PPD are 1 mM and 5.8 nM, respectively. In addition, the proposed UCCH biosensor is demonstrated to be of good selectivity and reproducibility for urea owing to the biological compatibility and structural stability of UCCH film.