Controlling the surface wettability of a biosensor improves the sensitivity and limit of detection (LOD) in an electrical label-free detection. The sensing area is treated as hydrophilic and its outer surface is treated as hydrophobic by using a passivation layer composed of CYTOP. The hydrophilic sensing area enhances biomolecule interactions between receptors and analytes, whereas the hydrophobic outer sensing region suppresses them. Consequently, the sensitivity and LOD are improved by the increased analyte concentration during the biomolecule interactions. We varied the areal ratio of the hydrophobic region to the hydrophilic region and investigated its effect via detection of cardiac troponin I, which is a biomarker that is used in determining the prognosis of myocardial infarctions. Threefold of sensitivity and 3 orders of LOD in the hydrophobic passivation were improved over the non-passivation.