Absorbance-Based Affinity Glucose Sensor

Abstract

ABSTRACT A fluorescence-based optical affinity glucose sensor which offers the advantage of equilibrium reactions has been developed. However, our efforts to miniaturize its optical components is hampered by unavailability of a suitable solid state emitter. An absorbance-based sensor is investigated to overcome the miniaturization difficulty of the optical system. A suitable dye is selected and tagged to the dextran. A small and portable optical detector using a photodiode and a red LED is fabricated. Our preliminary in vitro results indicates the feasibility of this approach as an ambulatory glucose sensor.1. INTRODUCTIONAn ambulatory glucose sensor that could continuously monitor blood glucose levels would greatly improve diabetic patient care and make a closed-loop insulin infusion system possible. Recently, a small optical glucose sensor for continuous in vivo monitoring of glucose has been developed.(1) The glucose detection is based on the reversible competitive binding of glucose and a high-molecular-weight fluorescence- labeled dextran (FITC-dextran) for sugar binding sites of a lectin, Concanavalin A (Con A). The sensing element consists of a short length of semipermeable hollow fiber containing immobilized Con A on its inner surface and FITC-dextran in the lumen. The concentration of the free (unbound) FITC-dextran is measured via a single optical fiber and is related to the glucose concentration.We have attempted to miniaturized the optical system and to developed an ambulatory glucose detector. Unfortunately, we could not find a suitable solid-state light source in the spectrum needed for the available fluorescent conjugates. As an alternative approach, we considered using a colored dye for two reasons: 1) dyes cover a wide range of the spectrum, and 2) the light throughput is high since no excitation or emission filter is necessary. This report describes the design and initial evaluation of an ambulatory absorbance-based affinity sensor for glucose.2. SENSOR FABRICATION2.1 Choice of dyeThere is a large number of dyes which cover a wide range of the spectrum. However, the choice is greatly limited by the specific requirements of the sensor. The dye must be nontoxic, have high extinction coefficient in the far red or near infrared, stable in aqueous solutions, and can be tagged to dextran. Approximately 30 dyes were screened and after considering all of the requirements, Procion Green was selected. The absorption peak of the the dye is at 630 nm.2.2 Dye-dextran taggingProcion dyes have the dichlorotiazinyl group which reacts with hydroxyl, amino or amide groups on the substrate to form a stable, covalent linkage.(2) The procedure for tagging the dye to dextran is essentially the same used for dying textiles.(3)