Reaction-field design by dry enzyme integration at exposed interdigitated electrodes for enhanced low-concentration glucose detection

Noninvasive glucose monitoring using saliva has garnered attention due to the ease of sample collection. However, salivary glucose concentrations are substantially lower than blood glucose concentrations and exhibit poor, variable correlation owing to compositional variations in saliva. This complicates the design of electrode interfaces capable of generating measurable signals from dilute analytes without separating the enzyme reaction zone from the transducer surface. This study integrates an exposed interdigitated Au electrode with a dry glucose oxidase layer to establish a reaction-field design concept for low-concentration glucose detection. The dry enzyme layer was integrated onto the electrode region via cold isostatic pressing, a straightforward, dry, heat-free process. Upon sample addition, the dry enzyme layer dissolved into the droplet, enabling direct contact between the exposed electrode and the reaction field. This configuration decreases the distance between the transducer and the active reaction zone, thereby enhancing low-concentration signal generation. The device exhibited glucose responses across 0.01–10 mM in phosphate buffer, encompassing the typical salivary glucose range. Although the response was influenced by integration pressure and enzyme loading, excessive pressing or loading reduced the response. These results indicate that reaction-field formation at the electrode interface—rather than merely stronger immobilization—primarily governs sensitive detection of low-concentration glucose in the present device. The findings provide a design basis for disposable low-concentration glucose sensors.