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 polymyxin B (PmB) immobilized on 4,4-dithiodibutyric acid coated gold electrodes. An equivalent circuit model with a constant phase element was used to interpret the obtained impedance spectra. The results indicated that the gold electrode after electrochemical polishing pretreatment in both 2-(N-Morpholino) ethanesulfonic acid (MES) and HClO4 solutions had a more effective surface state than that treated in H2SO4 solution. The changes in capacitance associated with a constant phase element on the PmB-modified electrodes were more sensitive, compared to those in the charge-transfer resistance, for detecting endotoxin over the 0.2-0.8 ng/mL concentrations. The activated and modified gold electrodes might be used to EIS detect endotoxin in real-time.
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