Photo-responsive oxidase mimic of conjugated microporous polymer for constructing a pH-sensitive fluorescent sensor for bio-enzyme sensing

The development of artificial enzyme mimics with high stability and good reusability is of great significance for the biosensing applications, and the utilization of light stimulation to regulate the catalytic activity of enzyme mimics has been attracting great interest. In this work, a photo-responsive conjugated microporous polymer (CMP) containing pyrazino[2,3-g]quinoxaline (CMP-PQx) was synthesized and found to have the function of effectively mimicking oxidase activity for the first time. Upon the irradiation by visible-light, CMP-PQx employed dissolved oxygen as electron acceptor to generate superoxide radicals for easily oxidizing various substrates. The CMP-PQx-modulated oxidation of thiamine to fluorescent thiochrome was found high pH-dependence toward a 0.2-pH unit change in the pH range of 4.6-8.6. Accordingly, a pH-sensitive fluorescence sensor was constructed for bio-enzymes that can hydrolyze their corresponding substrates to trigger pH changes. It was successfully demonstrated by the sensitive and selective detection of urease with a detection limit of 0.42 U/L and urease analysis in real saliva samples. This study opens the new application prospect of photo-responsive CMP materials for biomedical related sensing and obtained satisfactory results.