Soft-Probe-Scanning Electrochemical Microscopy reveals electrochemical surface reactivity of E. coli biofilms

Investigating and understanding dynamic biofilm growth mechanisms is challenging, often because state-of-the-art optical characterization tools provide limited information. Micrometric electrochemical imaging of Escherichia coli biofilms using Soft-Probe-Scanning Electrochemical Microscopy (Soft-Probe-SECM) is herein presented as a complementary technique. A soft microelectrode is scanned over biofilms in a gentle contact mode, which is essential to provide a constant working distance. The on-film reduction of an electro-active compound, here the oxidized form of ferrocene methanol, is used to create in situ biofilm metabolic activity maps by applying the feedback mode of SECM. SECM approach curves of identically grown biofilms suggest that the SECM-based detection of metabolic activity is surface-confined. The analysis could therefore be carried out on entire biofilms as well as on tape-stripped biofilm surface layers. The method is further capable of distinguishing between biofilms containing E. coli cells either with or without ampicillin-resistance. Finally, the SECM detection of the degradation of an E. coli biofilm in the presence of different gentamicin concentrations is presented.