Mercury thermometer-inspired test strip for concentration cell-based potentiometric detection of salivary α-amylase

In this work, we report on the mercury thermometer-inspired test strip for potentiometric detection of salivary α-amylase (sAA). The test strip contains a reaction chamber and two split channels, which are connected by a curved hydrophobic channel. The detection of sAA is based on sequential two-step reactions with preloaded reagents on the test strip. In the first step, maltose is produced by catalyzing the hydrolysis of starch using sAA in the reaction chamber. In the second step, the test strip is shaken to introduce the reaction mixture to the split channels under the inertia force, similar to the operation of a mercury thermometer. In one split channel, maltose reduces [Fe(CN)₆]^3- to [Fe(CN)₆]^4- under the alkaline condition, while the reaction hardly occurs in the other split channel with the neutral condition. This leads to a difference in the ratio of [Fe(CN)₆]^3-/[Fe(CN)₆]^4- between the two channels and therefore a potential difference that can be measured and correlated to sAA concentration. Using this test strip, sAA in the human saliva sample was quantitatively analyzed within 2 min. The application of this technique in the psychological evaluation was also demonstrated.