Portable electrochemical detection of salivary cortisol in self-driven microfluidic chip designed for trace liquid mixing

The real-time detection of cortisol in saliva is of great significance for the early non-invasive diagnosis of related diseases. In this work, a segmented micro-liquid mixing structure was fabricated using various passive valves, which can achieve the mixing of different liquids ranging from 0.3 to 0.5 μL, enabling efficient binding between cortisol antigens and antibodies. Moreover, by incorporating a capillary pump, self-driven liquid mixing can be accomplished without an external power supply. Electrochemical sensors for IgG and cortisol were prepared using the immunological sandwich method. Through the antibody-antigen-antibody sandwich structure, highly specific detection of IgG and cortisol within the range of 0.1–200 ng/mL was achieved, and the corresponding portable DPV detection circuit was designed and manufactured. By integrating the microfluidic chip, the sensor, and the miniaturized detection circuit into a POCT device, automatic detection of saliva cortisol can be achieved within 40–50 min. By adjusting the antibody modification in the sensor, the application of this physiological fluid POCT device can be expanded, and it may provide some inspiration for the development of portable non-invasive health management devices.