Continuous Glucose Detection Using Boronic Acid-Substituted Viologens in Fluorescent Hydrogels:  Linker Effects and Extension to Fiber Optics

A fluorescent anionic dye and a viologen appended with boronic acids, which serve as glucose receptors, have been synthesized and immobilized into a poly(2-hydroxyethyl methacrylate) hydrogel for use as a continuous glucose monitor. The fluorescence of the dye is modulated by the quenching efficiency of the viologen-based receptor, which in turn is dependent on the glucose concentration. Two monomeric versions of the quencher/receptor unit were prepared and their performance within the hydrogel evaluated. By tethering the quencher/receptor to the hydrogel matrix using a single-point attachment, slightly improved glucose sensing was observed. The hydrogels were tested for their ability to continuously and reversibly detect glucose over the course of several hours. The tests were carried out using a cuvette-based system, as well as a fiber-optic-based configuration. Under physiological conditions (0.1 M phosphate buffer, pH 7.4, 37 °C), the fluorescent hydrogels display an excellent dynamic response to glucose concentrations within the biologically significant range (2.5−20 mM).