In this work, we report on fabrication of the thin-films of silicon oxide dielectric layers on silicon with back-side contact and utilization of the structure to study the detection of human Troponin antigen (cTnI) molecules: the cardiac biomarkers for the early diagnosis of acute myocardial infraction. Aptamers are selectively bound to the target molecules and can block the binding epitope for further reaction like immobilization or interaction to any other molecules. In contrast to antibodies, the aptamers are smaller in size, which allows target molecules to be brought closer to the surface of the biosensor and, therefore, to enhance the molecular signal. The target molecule in this work is cTnI, which is located in the cardiac muscle tissue. As a reliable indicator of heart failure and injury, it is specifically considered for the diagnosis of myocardial infarctions. The solutions of Troponin molecules were studied in different concentrations range from 10 pg/μL to 1 ng/μL. For the electrical detection of cTnI, we used the field-effect capacitive electrolyte-insulator-semiconductor (EIS) technique, which is a robust method for the quantitative characterization of molecular layers. The measured values of capacitances and flat band voltages were used to acquire information about the properties of the molecular layers obtained using solutions with different troponin concentrations. It was shown that this method demonstrates high sensitivity to target cardiac biomolecules and opens up new perspectives for highly selective and sensitive cardiac biosensors developed on the basis of silicon nanowire structures.