Near-infrared fluorescence lifetime assay for serum glucose based on allophycocyanin-labeled concanavalin A

We describe an assay scheme for glucose based on fluorescence resonance energy transfer (FRET) between concanavalin A (con A), labeled with the nearinfrared fluorescent protein allophycocyanin (APC) as donor, and dextran labeled with malachite green (MG) as acceptor. Glucose competitively displaces dextran- MG and leads to reduction in FRET, assessed by time-domain fluorescence lifetime measurements using time-correlated single-photon counting. The assay is operative in the glucose concentration range 2.5-30 mM, and therefore suitable for use in monitoring diabetes control. Albumin and serum inhibit FRET but the interference can be prevented by removal of high molecular weight substances by membrane filters. APC shows promise for incorporation in an implanted glucose sensor which can be interrogated from outside the body.