Determination of Glucose by an Optical Biosensor Composed of a Molecularly Imprinted Polymer, Glucose Oxidase, and Bromothymol Blue

An optical biosensor was developed as a novel adsorbent to isolate glucose from saliva. A straightforward procedure was used to create the glucose-imprinted polymer coating on the surface of zeolitic imidazolate framework (ZIF-8) nanoparticles which served as the adsorbent. Glucose oxidase was immobilized. Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) analysis were used to characterize the novel adsorbent. The ZIF-8 nanoparticles were synthesized and coated with the MIP via precipitation polymerization on the surface of ZIF-8 nanoparticles with glucose acting as a template. To determine glucose, glucose oxidase catalyzed the conversion of adsorbed analyte on the polymer surface to gluconic acid. The resulting color change due to bromothymol blue was characterized using a colorimetric-based smartphone using the RGB profile. Key parameters such as pH, adsorbent mass, adsorption time, and indicator concentration were optimized and under these conditions this biosensor showed few interferences and good sensitivity with a 20 s response time. A linear range from 300 to 500 mg dL-1 was demonstrated by an exponentially growing calibration curve when saliva with pixel slopes (R + G + B) were used for calibration. This biosensor provides a low-cost and fast approach for glucose determination in biological samples.