4-(2-(4-methoxyphenyl)benzo[b]thiophen-3-yl)benzaldehyde (MPBB)-based chemical antibody is developed to detect CA125 (MUC-16) level more effectively via electrochemical methods. Novel MPBB is synthesized by using Pd-catalyst coupling reactions and electrophilic cyclization reactions. New benzothiophene structure is dispersed in Nafion solution and CA125 antigen was incubated on this electrode. Optimum conditions are found as 3 mu L MPBB loading, 30 ng/mL CA125 antigen concentration, and 90 min incubation time. Two distinct linear ranges of the electrode prepared at optimum conditions are determined by DPV as 5-50 ng/ml and 100-500 ng/ml. Limit of detection and limit of quantification values have been obtained as 0.03385 ng/mL and 0.10155 ng/mL, respectively. Interference and artificial serum results reveal that this electrode is a promising electrode for CA125 antigen determination for ovarian cancer. Binding energy is investigated by employing a molecular docking modeling study between CA125 antigen and MPBB. Electrochemical results and molecular docking results revealed that the MPBB is a promising alternative to marketed CA125 immunoassays.