**4.5 Nanotechnology-based antimicrobials used to control biofilms**

Currently, controlling biofilm formation by nanotechnology-based antimicrobials is of industrial interest, nanoemulsions and nanoparticles (NPs) with antibiofilm activity being an alternative to conventional methods.

Recently, some studies made on model system (polystyrene well plates) and real systems (fresh pineapple, tofu, and lettuce) indicated that nanoemulsions of EOs have significantly higher antibiofilm activity compared to pure EOs (**Table 2**). Antimicrobial efficacy of nanoemulsions is dependent on the droplet size and electrical properties of nanoemulsions [102, 103], nature of bacteria [75, 104], and food matrix [105–107].

Nanoparticles (NPs) can be used for both inhibition of biofilm formation and eradication of already formed ones [108].

In the last period, NPs with natural compounds gained increased interest because it was demonstrated that the inorganic capsules can protect the natural products with antimicrobial activity [109]. In this respect, cinnamaldehyde-encapsulated chitosan nanoparticles, garlic-silver NPs, and "tree of tee" oil NPs were used to combat biofilm formation by *P. aeruginosa* on polystyrene well plates and glass pieces [110–112]. Meanwhile, the biofilm formed by *S. aureus* on glass slide was inhibited by applying gold NPs with EO of *Nigella sativa* [113] and garlic-silver NPs [111].


**Table 2.**

*Antibiofilm activity of essential oil (EO) nanoemulsions.*

Metal-based NPs (silver, gold, and metal oxides) with antimicrobial activity can be used to create different nanocomposite materials able to prevent bacterial adhesiveness to food-contact surfaces and equipment. Wu and coworkers [114] showed that cysteine dithiothreitol and beta-mercaptoethanol were able to reduce *S. aureus* biofilm formation on polystyrene polymer. Liang and coworkers [115] revealed that silver salt of 12-tungstophosphoric acid NPs (AgWPA-NPs) can be used to develop new materials for preserving foods, since they were able to inhibit *S. aureus* biofilm formation by damaging bacterial cells' membrane. Moreover, genes related to biofilm formation, such as *icaA, sarA*, and *cidA* were shown to be downregulated as a consequence of AgWPA-NPs' application. Naskar and coworkers [116] tested the antibiofilm activity of polyethylene glycol-coupled Ag-ZnO-rGO (AZGP) nanocomposite on both Gram-positive bacteria (*S. aureus* ATCC 25923) and Gram-negative bacteria (*P. aeruginosa* MTCC 2453). These NPs, at a concentration of 31.25 μg/mL, reduced the biofilm formed by *S. aureus* with ~95% and that formed by *P. aeruginosa* with ~93%. Zinc oxide NPs were used for the destruction of the biofilm formed on glass slide by *S. aureus* and *P. aeruginosa* [117]. Titania nanoparticles can be used to prevent the formation of *P. fluorescens* biofilm on the surfaces of TiO2/polystyrene nanocomposite film [118]. It has been shown that nanostructured TiO2 combined with UVA irradiation can be used to destroy *L. monocytogenes* biofilm, while silver NPs at a concentration of 15 μg/mL had the capacity to inhibit *S. aureus* and *E. coli* biofilms [119, 120].

The ability of two types of superparamagnetic iron oxide (IONs and IONs coated with 3-aminopropyltriethoxysilane) to inhibit biofilm formation by *B. subtilis* was successfully tested by [121].
