Diabetes management is reliant on consistent and accurate monitoring. Low patient compliance for the standard finger prick test along with its intermittent nature may lead to undetected highs and lows. In 2014, poor glycemic control caused 207,000 hospitalizations from hyperglycemia and 245,000 hospitalizations from hypoglycemia in the US. The implementation of continuous glucose monitors (CGMs) can provide a more thorough illustration of blood glucose level fluctuations. Currently, there are several transcutaneous CGMs produced by Abbott, Dexcom, and Medtronic along with a fully implantable option by Eversense. Improvements to both the sensitivity and size of CGMs are being studied by our group through the development of a competitive binding, FRET-based, glucose biosensor that is fully implantable and probed optically with an external “watch-type” device. In previous work, our group has successfully developed an assay, but due to the near-UV excitation wavelength range, there are limitations in decreased skin penetration depth along with excess noise due to autofluorescence of the tissue. In this work, we investigated the FRET response through skin samples of both Blue (APTS) and near infrared (NIR) (Alexa Fluor 700 and 750) dyes. These dye samples were encapsulated within previously reported hollow, cylindrical, thermoresponsive hydrogel membranes and the fluorescence intensity signals were compared when placed beneath thin and thick (0.87 and 1.85 mm) rat skin samples. The FRET response of AF-700 and AF-700 was measured when placed beneath thicker skin samples of both lighter and dark pigmentations. The results indicate that the use of NIR dyes is needed to allow for a reasonable implantation depth for the implantable biosensor.
Central to minimizing the long- and short-term complications associated with diabetes is careful monitoring and maintenance of blood glucose at normal levels. Towards replacing conventionally used finger-prick glucose testing, indwelling continuous glucose monitors (CGMs) based on amperometric electrodes have been introduced to the market. Envisioned to lead to a CGM with an increased lifetime, we report herein a fluorescently-labeled competitive binding assay contained within a hydrogel membrane whose glucose response is measured via a novel portable system. The optical system design included a laser source, bifurcated fiber, laser filter and simple fiber coupled spectrometer to obtain the change in FRET pair ratio of the assay. Glucose response of the assay in free solution was measured using this system across the physiologic range (0-200 mg/dL). The FRET pair ratio signal was seen to increase with glucose and the standard error of calibration was 22.42 mg/dL with a MARD value of 14.85%. When the assay was contained within the hydrogel membrane’s central cavity and similarly analyzed, the standard error increased but the assay maintained its reversibility.
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