The use of impedance spectroscopy (IS) to detect and study bacterial growth has increased significantly in recent decades due to the availability of inexpensive and easy-to-use impedance sensors. In general, there is insufficient of information in the literature on impedance studies of bacterial sensors regarding the relationship between the components of the equivalent electrical circuit and the processes occurring on the sensor surface. To increase the sensitivity of measurement methods and sensor parameters, a deep understanding of the sensor response mechanism and its impact on impedance is required. IS method (AC f=4 Hz-8 MHz at a constant amplitude of 1 V) and Au/Pt IDE sensors were used to detect and monitor different concentrations (103, 106, 109 CFU/ml) of both live and dead bacterial cells (E.coli and S. aureus) prepared in deionized water (DH2O) and bacteria growth liquid (Mueller Hinton Broth, MHB). All measurements were conducted at temperature 24±1ºC and the immersion sample volume was 1 ml. The analysis of the impedance spectra based on Nyquist and Bode plots shows a significant difference in resistance with increasing concentration for both types of bacteria and the presence of characteristic changes in the low-frequency range. We also observed difference in the time dependences of impedance. The semicircle-shaped portion of the Nyquist plots obtained at high frequencies corresponds to the faradic transfer of electrons on the electrodes, while the spectrum obtained at low frequencies provides information on the diffusion process of transferring bacterial waste products in solution to the electrode surface. Ions formed as a result of bacterial cell growth increase the capacity of the double layer Cdl. The presence of live bacteria led to a decrease in the impedance value compared to dead cells, the value of Rs+Rct decreased about three times. The proposed method of bacterial cell selective detection can be used to identify two types of bacteria (E.coli and S. aureus), to qualitatively characterize the differences between dead and living cells, and estimate their concentration in samples with unknown number of bacteria per unit volume.
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DETECTION OF ESCHERICHIA COLI AND STAPHYLOCOCCUS AUREUS ON SENSORS WITHOUT IMMOBILIZATION BY IMPEDANCE SPECTROSCOPY
Published: 15 November 2023 by MDPI in 10th International Electronic Conference on Sensors and Applications session Chemo- and Biosensors
https://doi.org/10.3390/ecsa-10-16073 (registering DOI)
Keywords: Impedance Spectroscopy, IDE sensors, Bacteria detection, Escherichia coli, Staphylococcus aureus