Glucose sensors based on microcapsules containing an orange/red competitive binding resonance energy transfer assay

Fluorescent sensing systems offer the potential for noninvasive monitoring with implantable devices, but they require carrier technologies that provide suitable immobilization, accessibility, and biocompatibility while maintaining adequate response characteristics. A recent development towards this goal is a highly specific and sensitive competitive binding assay for glucose using apo-glucose oxidase (apo-GOx) as the recognition element and dextran as the competing ligand; this has been demonstrated as a glucose sensor system by encapsulating the competitive binding assay in semipermeable microcapsule carriers. This paper describes the extension of this sensor design to longer wavelengths in an attempt to increase the applicability to in vivo monitoring. The glucose sensitivity of the tetramethylrhodamine isothiocyanate-dextran (TD) and cyanine Cy5-apo-GOx (CAG) complexes showed five to 10 times greater specificity for beta-D-glucose over other sugars. Microcapsules loaded with TD/CAG complexes exhibited a linear, totally reversible response in the range of 0-720 mg/dL, with a sensitivity (percent change in intensity ratio) of 0.06%/(mg/dL). The decrease in sensitivity observed with the use of longer-wavelength dyes is most likely to be compensated with the deeper penetration of light and reduced tissue scattering. These findings imply that the encapsulation of sensing assay elements in microcapsules is a simple and translatable method for the fabrication of stable biosensors, and optimization of resonance energy transfer pairs and assay component preparation will further improve the response to approach clinically relevant performance.