Fluorescence Resonance Energy Transfer-Based Near-Infrared Fluorescence Sensor for Glucose Monitoring

Abstract

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.

Implantable fluorescence-based glucose sensor development

“…It is evident from this figure that the AF594 emission does not change due to the addition of glucose to the system, but the AF647 emission changes greatly. This result is an improvement to the change seen in previous publications using the traditional dextran Con A system [9][10][11][12] . The small changes seen in the AF594 emission are attributed to system noise and would therefore be compensated for by taking a ratio between the two emission peaks.…”

“…Current research has focused on the production of an implantable chemical sensor that allows for the continuous acquisition of interstitial fluid glucose levels (shown to be correlated to blood glucose) [8][9][10][11][12] . Previous work focused on using a poly(ethylene glycol) (PEG) hydrogel to encapsulate a chemical assay based on the affinity reaction between the protein Concanavalin A (Con A) and high molecular weight dextran 13 .…”

“…However, the overall change in fluorescence due to glucose has been reported to vary from 20% to 40% fluorescence recovery depending on the concentration of the various components and the sensing modality [9][10][11][12][13] . In order to successfully implant a sensor under the skin, detect, and quantify a change in fluorescent intensity, the overall response of the sensor to glucose must be maximized 16,17 .…”

Glucose Sensors Based on Microcapsules Containing an Orange/Red Competitive Binding Resonance Energy Transfer Assay

“…Recently, this work has been extended into the near-infrared (NIR) by labeling the dextran and Con A with an NIR donor-acceptor pair. 14,15 Because there are concerns over Con A toxicity and nonspecific binding, alternative RET-based glucose assays have also been developed using other glucose-binding proteins and genetically engineered proteins. [16][17][18] However, the sensitivity of these assays is too high for monitoring glucose levels typically found in the blood and intersitium.…”

Optical instrument design for interrogation of dermally-implanted luminescent microparticle sensors

“…However, fiber-optic systems require invasion by the probe and have not been proven to meet the stability or reliability requirements for long-term in vivo functionality. A potential solution for the probe interface is to detach the probe chemistry from the fiber tip, resulting in a completely implantable sensor [9][10][11][12][13]. A useful implantable device must be biocompatible, must not exhibit acute reagent consumption or degradation, and must provide means of communicating the sensor output to the physician or patient.…”