I immobilized thiol-modified ss_DNA first, then hybridized it with its corresponding DNA. Both the probe and the target were immersed in a 1M NaClO4 solution. After that, I backfilled with 1mM MCH and 1M NaClO4- for 2 hours. After that, when the electrochemical signal was tested with MB solution, the MB blue signal was very low, which was unexpected.