Endotoxin can lead to irreversible shock and death,underlying the necessity for development of facile,rapid,sensitive,and in situ methods to detect endotoxin.We used electrochemical impedance spectroscopy (EIS) to detect interaction of endotoxin with ssDNA immobilized on 3-mercaptopropionic acid coated gold electrodes.An equivalent circuit model with a constant phase element was used to interpret the obtained impedance spectra.The changes in capacitance associated with a constant phase element on the ssDNA modified electrodes were more sensitive,compared to those in the charge-transfer resistance.The activated and modified gold electrodes might be used to EIS detect endotoxin in real-time.