A new bioelectrode for gene detection of Mycobacterium leprae, also known as Hansen's bacillus, was produced by immobilizing of single-stranded DNA (ssDNA) with 78 bases long (specific gene related to Mycobacterium leprae) on graphite electrode modified with poly(4-aminophenol). This biosensing platform was able to recognize complementary DNA molecules via hybridization process. Hybridization between probe and target was monitored by voltammetry, using ferrocenecarboxyaldehyde as electrochemical DNA hybridization indicator. The hybridization of nucleic acid probe with the DNA target resulted in significant decrease in the oxidation peak current of ferrocenecarboxyaldehyde, indicating greater affinity of this compound for ssDNA than for double-strand DNA (dsDNA). The linear range of detection for the DNA target was found to be 0.35 - 35 ng/mu L. ssDNA hybridization with the DNA target was also investigated by electrochemical impedance spectroscopy (EIS), showing significant modification in Nyquist plot, by modification in electrode surface after addition of the complementary target. The effective immobilization of specific gene of Mycobacterium leprae onto graphite electrode modified with poly(4-aminophenol) and the detection of the hybridization process with the DNA target, monitored by voltammetry and EIS indicate that this is a new and promising biosensing platform to gene detection of Hansen's bacillus. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 2921-2928, 2010