tect different gram-negative (E. coli and P. aeruginosa) and grampositive
(S. aureus and S. epidermidis) bacterial species. Fig. 3c illustrates
the variation of the Δlog Z (%) as a function of bacteria
concentration for the four types of bacteria. It can be seen that all
bacteria induced changes in the dielectric properties of the sAMP
functionalized electrode but with different levels of sensitivity: the
highest Δlog Z (%) was observed with P. aeruginosa, followed by S.
aureus and S. epidermidis, which showed almost the same response,
and the least Δlog Z (%) was observed with E. coli. The
efficacy of the engineered sAMP to recognize the four bacteria and
the different selectivity behavior is largely unknown, however it
may be attributed to the different interactions between the sAMP
and bacterial membrane which vary among bacterial types (Beveridge,
1999; Schneewind et al., 1995). The difference of membrane
structure of gram-positive and gram-negative bacteria can
also influence the recognition ability and the electron transfer
process. For the gram-negative bacteria, the periplasmic space is