Enhancement of a fluorescent sensor for monitoring glucose concentration in diabetic patients

Abstract

The need for overnight and continuous monitoring of glucose levels in diabetic patients is profound, especially among juveniles. Implantation of a chemical assay which responds optically to changes in glucose concentration shows promise as a technology capable of continuously monitoring blood sugar with little invasion into the body. Previous fluorescent chemical assays, based on the affinity binding reaction between Concanavalin A protein and dextran, performed well but suffered from limited dermal penetration. In this work, a novel replacement for the dextran molecule (glycosylated dendrimer) was fabricated and tested to determine if it would improve the overall response of the sensing chemistry to glucose. Experiments were carried out and it was found that the assay’s functionality was based on the controlled aggregation of the Con A protein and the modified dendrimer molecule. This new assay proved to be specific to glucose, reversible, and independent of fluorophore dye attached to the protein. This research was furthered by encapsulation of the new assay into a PEG hydrogel which showed response to glucose but, due to leeching, did not perform well under repeated exposures. A new method for encapsulation was proposed based on poration of the hydrogel to create micropores capable of holding the assay chemistry and allowing it to react to incoming glucose, while the surrounding polymer restricted leeching. Preliminary results with previous assays proved the potential of a mannitol based poration procedure, but unforeseen complications in lyophilization of the new sensor assay restricted its completion. Due to instability of Con A in solution, it was hypothesized that the immobilization of it onto the surface of an active substrate would increase its stability overtime as seen in previous works. The immobilization procedure was performed on Con A for both polystyrene spheres and gold (nanoshells and colloid). Both results showed an adequate amount of protein on the surface of the particles, but little binding activity was demonstrated. Overall, the improvements to the sensor chemistry response were notable and the potential for stabilization and enhancement of the response through the use of an active substrate is promising.