Continuous glucose sensing with fluorescent thin-film hydrogels. 2. Fiber optic sensor fabrication and in vitro testing.

BACKGROUND There continues to be a need for better sensors for continuous glucose monitoring. We are working on a two-component sensing system based on a viologen boronic acid and a fluorescent dye, which are immobilized in a hydrogel. This system has the potential for further development into a real-time glucose-monitoring device. The current study reports the fabrication of sensors using preformed hydrogels and the first in vitro monitoring of glucose concentrations in a prototype sensor configuration. METHODS Glucose sensing hydrogels containing a fluorescent dye and viologen boronic acid quencher were preformed in a mold. These preformed hydrogels were then attached to the distal end of a plastic fiber optic cable using different adhesives to prepare the in vitro sensors. These sensors were connected to a flow cell and monitored using a fluorescence spectrometer. The fluorescence emitted by the hydrogel changes depending on the glucose concentration. Hydrogel components were modified in order to optimize the performance of the sensors. RESULTS A soft tissue adhesive used by veterinarians was found to be an effective adhesive for bonding the hydrogel to the fiber tip. This adhesive did not affect the glucose sensing ability of the hydrogels after fabrication. Several sensors were fabricated with varying composition of sensing elements, and all of them showed stable and reversible glucose response. The glucose signal was found to be stable over months on repeated testing. Glucose sensing studies using the sensors with hydrogels containing different compositions of sensing elements showed that the ratio of dye to quencher is an important parameter in determining the magnitude and linearity of glucose response in the biological range. The response time of the sensor was shown to be dependent on the hydrophilicity of the hydrogels. Modifying the hydrogels with ionic comonomers shortened the response time. CONCLUSIONS The combination of the anionic dye 2 and viologen-based boronic acid 1 immobilized in a 2-hydroxyethyl methacrylate hydrogel functions well in a fiber optic configuration. This preliminary study suggests that the two-component sensing system has several advantages in terms of stability and ease of fabrication. Improvement of the configuration of the sensor and further development of the sensor towards application for in vitro study are underway.