The paper presents a biosensing system for antibody detection based on Differential Impedance Sensing by nanobead amplification able to perform high resolution measurements down to few beads counts. A pair of gold micro-electrodes in differential configuration ensures rejection of drift in solution temperature and ionic content. The biosensor has LOD below 100 pg/ml concentration of primary antibody in buffer. An electronic reading board based on FPGA module performs multifrequency lock-in impedance tracking in portable configuration. The system hold promises for rapid and specific detection of selected antibody with clinically relevant concentrations for rapid immunotesting in a point of care setting.