Potential of Metal Oxide Nanoparticles and Nanocomposites as Antibiofilm Agents: Leverages and Limitations

Abstract

Metal oxide nanoparticles (MONs) emerged as antimicrobials due to the occurrence of multidrug-resistant (MDR) bacterial strains. Antimicrobial activity has been shown to be influenced by the route of synthesis and precursors. Hence, a plethora of literature exists on prominent MONs like Ag2O, CuO, ZnO, TiO2, MgO, Al2O3, and Au, as activity was influenced by physicochemical parameters which are influenced vis-a-vis by new synthesis methods. Conventionally or controversially, researchers looking for antimicrobial activity still predominantly conduct testing on planktonic cells irrespective of application. It is now evident that microbes follow a biofilm mode of living. However, an outcome from these revealed that the actions of MONs were strain specific and dependent on positive charge of NP with smaller size, demonstrating better bactericidal effects. No given NP has been shown to exhibit a broad-spectrum activity under in situ conditions at low concentrations, which is a prerequisite for successful development as a product for environmental/public hygiene applications. This trigged the testing of polymetallic oxide (PMNO)/bimetallic nanoparticles toward broad-spectrum activity which indeed was more effective. Again these evaluations were restricted to individual strains and not at the community level. Biofilms are the preferred mode for most microbes, and biofilm formation is ubiquitous and a surface-associated phenomenon. Control measures should therefore aim at eliminating biofilms, which also serve as a reservoir of microbes. In-lieu of these, realizations have fuelled new research, like using NP as nanofillers, surface immobilization of NP into different polymeric substrates for varied applications. Currently, polymer nanocomposites and surface modifications are the mainstay, and a paradigm shift in studies testing these formulations for inhibition of biofilm formation has resulted in the development of several new antibiofilm and antifouling coating formulations.