A Layer-by-Layer Approach To Retain a Fluorescent Glucose Sensing Assay within the Cavity of a Hydrogel Membrane

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Abstract
A continuous glucose monitoring (CGM) device that resides fully in the subcutaneous tissue has the potential to greatly improve the management of diabetes. Towards this goal, we have developed a competitive binding glucose sensing assay based on fluorescently-labeled, PEGylated-concanavalin-A (PEGylated-TRITC-ConA) and mannotetraose (APTS-MT). Herein, we sought to contain this assay within the hollow central cavity of a cylindrical hydrogel membrane, permitting the eventual subcutaneous implantation and optical probing through the skin. A ‘self-cleaning’ hydrogel was utilized due to its ability to cyclically deswell/reswell in vivo, which is expected to reduce biofouling and so extend the sensor lifetime. Thus, a hollow, cylindrical hydrogel was prepared based on a thermoresponsive, electrostatic double network (DN) design composed of N-isopropylacrylamide (NIPAAm) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS). Next, a layer-by-layer (LbL) coating was applied to the inner wall of the central cavity of the cylindrical membrane and consisted of 5, 10, 15, 30 or 40 alternating bilayers of positively charged, poly(diallyldimethylammonium chloride) (PDADMAC) and negatively charged, poly(sodium 4-styrene¬sulfonate) (PSS). With 30 bilayers, the leaching of the smaller sized component of the assay (APTS-MT) from the membrane cavity was substantially reduced. Moreover, this LbL coating maintained glucose diffusion across the hydrogel membrane. In terms of sensor functionality, the assay housed in the hydrogel membrane cavity tracked changes in glucose concentration (0 to 600 mg/dL) with a mean absolute relative difference (MARD) of ~11%.
Funding Information
  • National Institute of Diabetes and Digestive and Kidney Diseases (1R01DK095101-01A1)
  • Division of Engineering Education and Centers (EEC-1648451)

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