Ultra-sensitive detection of pathogenic microorganism using surface-engineered impedimetric immunosensor

A label-free electrochemical immunosensor for highly sensitive and specific detection of pathogenic bacteria is described. To increase the sensitivity of electrochemical impedance spectroscopy (EIS) based immunosensor the surface of gold electrode was engineered with a biocompatible and hydrophilic layer of hyaluronic acid (HA) which greatly enhanced the capture efficiency of model microorganisms, Escherichia coli O157:H7 through anti-E. coli O157:H7 antibody conjugated onto the HA layer. For quantitative detection, the magnitude of impedance at 0.1 Hz in the presence of redox probe, [Fe(CN)6]3−/4−, was analyzed by normalized impedance change (NIC) with respect to varying concentration of target bacteria. The magnitude of impedance at 0.1 Hz increased linearly with the concentration of target bacteria (10–105 cfu/mL) with an extremely low limit of detection (∼7 cfu/mL). This is by far one of the most sensitive non-PCR based sensors for bacterial detection. The responses of this system against non-target bacteria, Staphylococcus aureus, Bacillus cereus and non-pathogenic E. coli DH5α were negligible even at a high concentration, which confirms the highly specific nature of antibody–HA modified immunosensor.