Fluorescence resonance energy transfer-based near-infrared fluorescence sensor for glucose monitoring

A novel near-infrared (NIR) fluorescence affinity sensor for continuous glucose monitoring was developed and characterized. The sensor operates by fluorescence resonance energy transfer between a NIR chromophore linked to concanavalin A (ConA) and an NIR fluorophore linked to free dextran. The binding of dextran with ConA in the absence of glucose results in low fluorescence due to quenching; however, the quenching is reversed by competitive displacement of dextran from ConA by glucose. In order to increase thermodynamic stability and the lifetime of the sensor, ConA was immobilized within a macroporous bead matrix. The sensor was contained within a sealed hollow dialysis fiber (o.d. 215 microm, wall thickness 20 microm), preventing the macromolecules from leaking out and enabling glucose to rapidly enter the fiber lumen. A glucose-insensitive reference fluorophore was also incorporated to allow for ratiometric measurements, resulting in a robust sensor output that is independent of positional and/or light intensity changes. The response of the fluorescence affinity sensor to glucose was tested continuously in an automated test chamber at 37 degrees C. The sensor showed good dynamic range within physiologically relevant glucose concentration range (15% change over 2.5-30 mM, no hysteresis), fast response time (2-4 min), and a remarkable long-term stability (6 months). We interpret the improved longevity of this sensor to be the result of an optimized photo exposure regime and immobilization of ConA to the matrix. Its small size, ratiometric output, and NIR fluorescence make this sensor well suited for dermal implantation and continuous transdermal monitoring.