Competitive binding assays in microcapsules as "smart tattoo" biosensors

This paper demonstrates a novel fluorescence resonance energy transfer (RET) sensor system, wherein a competitive binding (CB) assay is encapsulated into microcapsules. For CB approaches intended as smart tattoos, microcapsules are superior to hydrogel microparticle systems, as they provide space in the capsule interior for the free movement of the sensing elements while maintaining constant sensing assay concentration. Previously-developed CB glucose sensors suffer from toxicity, nonspecificity, lack of efficient encapsulation technology, and poor reversibility. To overcome some of these limitations, apo-glucose-oxidase (AG) was used as a glucose binding protein and was entrapped in polyelectrolyte microcapsules. The glucose-sensitive change in RET of the fluorescein isothiocyanate (FITC)-dextran and tetramethylrhodamine isothio-cyanate (TRITC)-AG entrapped in microcapsules showed 5times more specificity towards glucose over other sugars, with a sensitivity of 0.035units/mM in the range of 0-40mM. These response characteristics appear to be suitable for glucose monitoring in diabetic patients