A novel terthiophene-3-carboxylic acid compound is disclosed that a functionalized conductive terthiophene polymer having carboxylic groups produced in an electrochemical method using the compound as a monomer and a novel process for detecting DNA hybridization through impedance measurement using the polymer. In addition, a method for manufacturing a probe DNA used in the process for detecting DNA hybridization is provided. Since the process can detect DNA hybridization using impedance change, without the use of any indicator, small-sized sensor systems which measure impedance in a particular frequency range can be fabricated. The systems are applicable to portable sensors for identifying DNA sequence hybridization for clinical examination and disease diagnosis. Further, the process has an excellent selectivity of complementary sequences to mismatched sequences.