We present a novel method for label-free detection of cytokines in serum after ten minutes of stabilization at nanomolar concentrations. Detection of proteins in blood using label-free impedance-based techniques is difficult due to high salt concentration of the matrix, which results in screening of the charge of the target proteins. The microwell array design provides enhanced electrochemical sensitivity by electric field focusing in the wells. We describe an on-chip multiwell plate sensing configuration where sensitivity benefits from the high salt concentration of the matrix and demonstrate robust performance through testing in rat serum.