Secretory immunoglobulin A (s-IgA), found in biological fluids, is useful for monitoring condition on mental health to prevent depression. In this study, the non-invasive detection of s-IgA in human sweat was demonstrated using field effect transistor (FFT) bioscnsors modified with a plant lectin, jacalin, as a receptor. The s-IgA molecules were detected with greater sensitivity using the jacalin-immobilized FET biosensors as compared to the sensitivity shown by Fabimmobilized FET bioscnsors. Jacalin, which is a small lectin tetramcr, has four glycan-binding sites and can capture a large number of s-IgA molecules within the charge-detectable region in terms of Dcbye length. Moreover, the jacalin-immobilized FET bioscnsor could detect s-IgA at concentrations ranging from 0.1 mu g/ml. to 100 mu g/mL Additionally, by using a filtration process to eliminate the interference of other components found in human sweat, our FET sensing system could specifically and quantitatively detect s-IgA. Therefore, our results show the utility of this device in monitoring mental stress.