Miniaturization of immunoassay by using a novel module-level immunosensor with polyaniline-modified nanoprobes that incorporate impedance sensing and paper-based sampling

This work presents a module-level impedance measurement system integrated with a disposable immunosensor for the immunoassay of bladder cancer cell lysate (T24) to a specific antibody (galectin-1). The immunosensor consisted of a flexible printed circuit patterned with an interdigital microelectrode array which immobilized polyaniline-modified nanoprobes on an electrode surface by dielectrophoresis. A quantitative sampling of cell lysate without a pump was made by using paper as the cell lysate carrier and sweeping a moistened paper over the sensing area of interdigital microelectrode array for sampling. In this study, the impedance measurement results of the module-level system were compared with those measured by the precision LCR meter, in which the error is <2 %. Additionally, the normalized impedance variation in immunosensing linearly increased with the cell lysate concentration. With a sensitivity based on a normalized impedance variation of 124.4 % per mg/ml, the immunosensor can rapidly detect the lowest concentration of cell lysate for 0.0626 mg/ml in 10 min. Therefore, this work has demonstrated the accuracy of the module-level immunosensor as well as the reliability of impedance-based sensing for bladder cancer cell lysate. The proposed disposable sensor and portable impedance system module are highly promising for use in point-of-care diagnostics.