Development of an immersion-type hydrogel-integrated microfluidic glass fiber-based analytical device and its application to smartphone-assisted glucose colorimetric assay.

Microfluidic paper-based analytical devices (μPADs) are attractive platforms for on-site analysis; however, quantitative analysis remains challenging because sampling strongly influences analytical performance. Existing sampling methods often require precise volumetric sampling or operator-dependent handling, which involves an inherent trade-off between analytical simplicity and quantitative reliability. To overcome this limitation, herein, we propose the concept of a quantitative assay using an immersion-type hydrogel-integrated microfluidics glass fiber-based analytical device (IHμGFAD). The IHμGFAD consisted of a reagent-encapsulated hydrogel for reaction/detection with a glass fiber channel for sampling. The combination of the hydrogel with the glass fiber channel was realized by exploiting the self-adhesive property of hydrophobic patterns fabricated using a liquid crystal display 3D printer. The immersion-based quantitative assay using the IHμGFAD was demonstrated with a glucose oxidase/horseradish peroxidase-based glucose colorimetric assay as a model system. The limit of glucose detection (3σ) was estimated to be 68 μM. The immersion-based assay was also applied to the quantification of glucose in human serum controls and pooled human serum, demonstrating its potential applicability to real-sample analysis. The immersion-based assay provides a μGFAD-based analytical method that achieves both practical user-friendliness and reliable quantitative performance, and it contributes to the advancement of on-site quantitative analysis in a wide range of fields, including healthcare, environmental monitoring, and food safety.