Rapid and label-free differentiation of bacterial strains using low frequency electrochemical impedance spectroscopy

Microinterdigitated electrode structures (μIDES) have widely been used for electrochemical cell impedance spectroscopy (ECIS). For instance ECIS has been used to study biofilm formation and growth of a wide range of microorganisms to detect bacterial infections, food contaminations, biocorrosion, and biofouling. In this study we describe the development of a label-free bioassay to determine the presence of different bacteria strains using ECIS. Following initial characterization of embedded gold μIDES using solutions of increasing conductivities, impedance spectra ranging from 10Hz to 300 kHz in the presence of Bacillus subtilis DMS10 and Shewanella oneidensis MR-1 were recorded over a period of approx. 5 hours. Frequency analysis showed that at 30 Hz the impedance response differences were higher and the relative standard deviations were smaller between each strain and the medium. In contrast to standard cell impedance sensing, which is performed at frequencies higher than 10 kHz to detect cell membrane polarizations, our low frequency results indicate that ionic changes at the electrode-solution double layer (C_dt) resulting by individual bacterial metabolism, can also be used to non-invasively and label-free differentiate microorganisms.