A smartphone-assisted “all-in-one” paper chip for one-pot noninvasive detection of salivary glucose level

Noninvasive glucose detection for diabetes monitoring, in comparison with the conventional finger-prick test that causes inevitable pain, is on demand. Salivary glucose level that possesses a well-established correlation with blood glucose level can be a promising alternative for noninvasive detection, however, the sensitivity and user-friendliness remained to be improved. Herein, an “all-in-one” paper chip was fabricated by one-pot method for sensitive and user-friendly detection of salivary glucose level. Glucose oxidase (GOx) and the chromogenic reagent, luminol, were both in situ encapsulated in a metal–organic framework, ZIF-67, to form the GOx&luminol@ZIF-67@Paper (G&L@ZIF@Paper). Owing to the specificity of GOx and the peroxidase activity of ZIF-67, the paper chips are highly sensitive and specific for glucose with a linear range from 0.2 to 2 mM, and a limit of detection of 0.12 mM (S/N = 3). Moreover, ascribing to the protection and “all-in-one” structure by ZIF-67, the chip is highly stable that maintains the detection performance after storage at room temperature in air for 4 weeks, and this strategy also facilitates the one-pot detection without multiple steps of sampling and incubation. With the assistance of a smartphone application, the glucose level in saliva can be accurately detected with “sample-in-result-out” manner, and the results were highly consistent with those measured by commercial kit. This paper chip is a promising device for daily glucose monitoring, and the highly-integrated strategy provides an innovative resolution for the construction of colorimetric paper chips.