DOPAMINE MODIFIED HYDROGEL MICRONEEDLE BIOSENSOR FOR KETONEBODY SENSING

Ketoacidosis, a severe complication primarily occurring in type1 diabetes due to insulin deficiency, results in the body utilizing fats for energy, leading to excessive ketone production and acidity.Monitoring HB levels is crucial for type1 diabetes patients to prevent ketoacidosis 1 , especially as the rise in the ketone level can be assumed as an early indicator of insulin deprivation.Hence, monitoring the level of HB is important to type1 diabetes patients since they are more prone to experience ketoacidosis 2 .Microneedles are a new platform suitable for minimally invasive systems.Some metallic Microneedle systems have been developed for ketone monitoring; however, there is a high risk of needle breakage and, consequently infection in the insertion area.In contrast, hydrogel microneedles are a potent option for ketone sensing due to their biocompatibility 3 , anti-biofouling 4 features, inherent properties in hydrogels.In the current study, the -Hydroxybutyrate Dehydrogenase (HBD) enzyme together with its cofactor NAD + was integrated into the hydrogel microneedle (Dopaminated Hyaluronic acid mixed with PEDOT:PSS).NADH as a secondary product of the enzymatic reaction is electrochemically active making it possible for electrochemical sensing; however, the anodic reaction has an overpotential 5 .Using a redox mediator is an established technique to decrease the NADH overpotential 6 .Dopamine (dual-functional component) was employed in the current study as redox mediator and cross-linking agent, the first hydrogel microneedle for continuous ketone body sensing.The interaction of NADH with dopamine was confirmed in in-vitro studies (Figure1A,1B).To this end, a positive sweep was performed to convert catechol moieties of dopamine solution into quinone which later reduced to catechol concomitantly with NADH oxidization.By increasing the concentration of NADH, a rise was observed in the anodic peak (Figure1D); conversely, a decrease in quinone (Figure1E).Ex-vivo studies were performed on porcine skin, Microneedle patches were applied on the skin equilibrated with different concentrations of HB.Chronoamperometry current (0.3 V) was recorded for 20 seconds, designated as pre-oxidation current; followed by 10 seconds accumulation time.Then, chronoamperometry (0.3 V) was performed for 50 seconds, designated as detection current.The normalized current was defined as the ratio of detection current to pre-oxidation current.A linear response was observed for HB concentration below 1.5 mM with a sensitivity of 0.09/mM (Figure2B).Additionally, the mechanical properties of the microneedle patch were evaluated by compression mechanical test.The microneedle patch could tolerate the forces much higher than the required force (0.3 N/needle) for skin penetration (Figure2C); also, SEM images confirmed the intact structure of Microneedles (Figure2D).Streptozocininduced diabetic rats were used as animal model for in-vivo studies.Microneedle patches were applied on the back of the rat and fixed with Tegaderm.Then, the ketone level was measured by both the microneedles patch and ketone strips (blood in the tail) using the Freestyle Libre ketone meter.We calculated a MAD (mean absolute difference) of 0.184 mM for ketone levels < 1.5 mM and a MARD (mean absolute relative difference) of 7.68% for ketone levels of 1.5 mM.