Photocrosslinked dextran hydrogel coatings with FAD-glucose dehydrogenase for continuous glucose monitoring in complex media: Key role of methacrylation degree on bioelectrocatalytic activity and sensor stability

ABSTRACT Fungal flavin-dependent glucose dehydrogenase (FAD-GDH) is now widely preferred as an O 2 -insensitive alternative to glucose oxidase for 2 nd generation blood glucose test strips. FAD-GDH bioelectrodes have potential for continuous glucose monitoring (CGM), but continue to be hampered by poor operational stability, restricted mediator compatibility, and selectivity limitations. Herein, we report new protective biosensor coatings based on covalently photocrosslinked polysaccharides for more robust CGM with FAD-GDH bioelectrodes. The crosslinked hydrogel membranes were prepared from dextran methacrylate (Dex-MA) polymers synthesised with different degrees of substitution (DS = 9%, 18%, and 37%). The polymers were dip-coated then crosslinked via a photoinitiator using a rapid visible light process (λ = 405 nm; 1 min). This study highlights the crucial impact of the polymer DS on redox mediator electroactivity, O 2 reactivity, catalytic glucose activity, storage stability and operational stability. A higher polymer DS provided improved mediator stabilisation and up to a 4-fold increase in 1-week storage stability. A high DS of 37% also significantly increased CGM stability and permitted attractive sensor analytics in artificial interstitial fluid (ISF). The three sensors prepared with a DS of 9% to 37% provided practical linear ranges and detection limits for CGM. A CGM lifetime of 54 h was achieved in a complex artificial ISF comprising electroactive interferences, compared to only 16 h for an equivalent biosensor without hydrogel protection. Photocrosslinked polysaccharide hydrogel membranes hold promise for extending bioelectrocatalytic outputs for future biosensors and eventually biofuel cells and bioreactors.