# Electrochemical Control of Biofilm Formation and Approaches to Biofilm Removal
## 4 Electrochemical Biofilm Control
### Electrochemical Communication during Biofilm Formation
#### 4.2.2 Electrochemical Mapping of Biofilm Location  
The previous chapter suggests that bacterial cells are capable of exhibiting electrical activity which can be electrochemically monitored. In addition to the predominant spectral and microscopic methods [81], electrochemical approaches can also find their application in the mapping of biofilm location. Scanning electrochemical microscopy (SECM) [174] with its complementary technique of soft-probe-scanning electrochemical microscopy (Soft-Probe-SEM) [175] have proved themselves in the characterization of biofilms. Although SECM is being recommended as a suitable method for studying interactions in biofilms, it is still a desktop and large device not very suitable for the online monitoring of biofilm formation.  
Fortunately, an electrochemical impedance spectroscopy (EIS) can be chosen instead, representing a nearly ideal tool for the non-contact electrochemical evaluation of biofilms [176]. In 2013, it was confirmed that it is capable of being operated in real time for the non-destructive monitoring of _Pseudomonas aeruginosa_ biofilm, when its growth and metabolic activity was investigated using a combination of multi-channel impedance and amperometric sensors, respectively [177]. Numerous reports have shown that the electrochemical mapping of biofilm location can be performed using a multi-electrode array (MEA) system [178; 179; 180; 181] integrated in the biofilm impedance chamber, as shown in Figure 5. MEA chips designed in this way represent promising devices for the control of microbiologically affected corrosion (MIC) related to sulfate-reducing bacteria (SRB). In 2015, a multi-electrode array (MEA) system was used for the monitoring of spatiotemporal electrical activity during the development of _Bacillus licheniformis_ and _Pseudomonas cal caliphila_ biofilms. Based on the data obtained, it was demonstrated that the intensity of the electrical activity did not linearly depend on the bacterial density, but it was instead correlated with biofilm formation [181]. Unfortunately, such a real-time electrochemical monitoring system was examined only in small reactors under laboratory conditions. In the near future, it can be assumed that the MEA chip will be directly installed into food industry processing equipment to verify its applicability.  
Figure 4: Direct electron transfer mechanisms via membrane-attached cytochrome (short distance electron transfer) (**A**), soluble redox mediator (**B**), and conductive pilli (long distance electron transfer) (**C**).  
In addition to the above-mentioned approach utilizing the impedance measurement, several studies demonstrated the usefulness of cyclic voltammetry [182, 183] and Tafel analysis [182] at standard disc electrodes, with both these methods providing valuable information about bacterial attachment and biofilm formation [184]. For this purpose, the electrochemical reversibility of a redox marker is monitored over a period of time.  
Biofilm location can be also determined using nano-engineered microbial electrochemical systems (MESs) based on voltammetric measurement with nanostructured electrodes that contain hyperbranched chitosan nanoparticles (HBCs) and reduced graphene oxide (rGO) nanosheets. In this case, the shapes of cyclic voltammograms obtained (increase in background current response) have indicated the individual phases of biofilm formation [183].