Capillary-driven, superhydrophilic microfluidic retainer for continuous salivary glucose monitoring

Salivary glucose monitoring provides a non-invasive alternative to blood-based diabetes tests; however, low analyte levels and unstable microfluidic wetting have hindered its translation. Here, we introduce a retainer-based microfluidic system that integrates a capillary-driven, superhydrophilic microchannel with a miniaturized three-electrode enzymatic sensor for continuous salivary glucose monitoring. This device maintains sustained hydrophilicity for at least 120 days without compromising flexibility or biocompatibility. The gold working electrode, functionalized with glucose oxidase immobilized in a carbon nanotube-chitosan matrix and a thin glutaraldehyde overlayer, offers sensitive and stable detection. The integrated sensor shows a chronoamperometric sensitivity of 15.48 μA mM^-1 cm^-2 and a limit of detection of <42 μM. The in vitro measurements using glucose-spiked artificial saliva show the reproduced postprandial profiles with rapid signal stabilization and high run-to-run repeatability over three cycles. Overall, this work captures the potential of the retainer-based microfluidic system as a practical pathway toward continuous, non-invasive salivary glucose monitoring.