Smartphone-based point-of-care testing of salivary α-amylase for personal psychological measurement.

Here we report a smartphone-based potentiometric biosensor for point-of-care testing of salivary α-amylase (sAA), which is one of the most sensitive indices of autonomic nervous system activity, and therefore a promising non-invasive biomarker for mental health. The biosensing system includes a smartphone having a sAA-detection App, a potentiometric reader and a sensing chip with preloaded reagents. The saliva sample wicks into the reaction zone on the sensing chip so that the sAA reacts with the preloaded reagents, resulting in conversion of an electron mediator Fe(CN)6(3-) to Fe(CN)6(4-). The sensing chip is then pressed by fingers to push the reaction mixture into the detection zone for the potentiometric measurement. The potential measured by the smartphone-powered potentiometric reader is sent to the smartphone App via the USB port, and converted into sAA concentration based on a calibration curve. Using our method, sAA in real human sample is quantitatively analyzed within 5 min. The results are in good agreement with that obtained using a reference method, and correlated to psychological states of the subjects.