Detection of Escherichia coli bacteria by impact electrochemistry

Since 2015, most reports in single-impact electrochemistry of bacteria concern E. coli as a model bacterium.

“Since 2015, most of the reports in this area concern Escherichia coli (E.coli) as a model bacterium but this sensitive electro-analytical technique has not proved to be efficient for selective detection yet, except for the discrimination between Grampositive and Gram-negative bacteria [30,32].”

Several studies deal with the use of redox mediators for probing the electrochemical activity of a bacterium.

“In order to develop single-impact electrochemistry toward the identification of bacterial cells, several studies deal with the use of redox mediators for probing the electrochemical activity of the bacterium [32][33][34].”

Single-impact electrochemistry has not proved efficient for selective detection of bacteria yet, except for discrimination between Gram-positive and Gram-negative bacteria.

“Since 2015, most of the reports in this area concern Escherichia coli (E.coli) as a model bacterium but this sensitive electro-analytical technique has not proved to be efficient for selective detection yet, except for the discrimination between Grampositive and Gram-negative bacteria [30,32].”

Lee et al. demonstrated a linear relationship between collision frequency f_exp and E. coli concentration C_bac, as expected by Equation 1.

“The authors have demonstrated a linear relationship between the collision frequency f exp (number of step-shaped transients) and the E. coli concentration C bac , as expected by Equation 1 below (in conditions where the mass transport is controlled by diffusion) [10,16,32].”

The TMPD technique is an efficient method to discriminate living bacteria from dead ones (no cytochrome c oxidase activity).

“This technique is an efficient method to discriminate living bacteria from dead ones (no cytochrome c oxidase activity) and it also shows the expected linear relationship between the collision frequency and the E. coli concentration in solution (see Equation 1) [32].”

When bacteria enter the diffusion layer, a feedback redox cycle is created and a reductive current spike is detected, corresponding to regeneration of TMPD•+ in the periphery of the bacterium.

“When the bacteria enter the diffusion layer, a feedback redox cycle is created and a reductive current spike (current increase) is detected in the chronoamperometry measurement, corresponding to the regeneration of TMPD •+ in the periphery of the bacterium (Fig. 3a) [32].”

Couto et al. deals with the use of TMPD as a redox mediator, which enables electrochemical recognition of bacterial cytochrome c oxidases without the need of cell lysis.

“For the detection of E. coli by impact electrochemistry, the work of Couto et al. deals with the use of N,N,N',N'tetramethyl-para-phenylene-diamine (TMPD) as a redox mediator, which enables the electrochemical recognition of bacterial cytochrome c oxidases without the need of cell lysis (Fig. 3a) [32].”

Because E. coli cells include cytochrome c oxidases in their membranes, they are able to oxidize extracellular TMPD to TMPD•+.

“Because E. coli cells include cytochrome c oxidases in their membranes, they are able to oxidize extracellular TMPD to TMPD •+ .”

The TMPD technique shows the expected linear relationship between collision frequency and E. coli concentration in solution.

“This technique is an efficient method to discriminate living bacteria from dead ones (no cytochrome c oxidase activity) and it also shows the expected linear relationship between the collision frequency and the E. coli concentration in solution (see Equation 1) [32].”