Bacterial infections are said to be one of the paramount threats to human health. However, because of the increasing spread of multidrug-resistant bacteria, the present antibiotic reservoir seems to be inadequate, thus demanding the exploration of novel antibacterial agents. Nano-antibacterial agents signify a unique strategy for bacterial killing.
In contrast to antibiotics, nano-antibacterial agents have the following two benefits: i) wide-spectrum bactericidal effects against Gram-positive and Gram-negative bacteria and ii) enduring bactericidal impact on the prevention of bacterial growth because of their astonishing stability. Substantial differences exist in the antibacterial mechanisms between nano-antibacterial agents and antibiotics. Antibiotics can prevent bacterial growth by hindering the synthesis of target biomolecules in bacteria, including DNA, cell wall, and proteins. However, nano-antibacterial agents can destroy bacteria through the mechanisms of oxidative stress response and membrane destruction and by the interactions with cytosolic molecules (lipid, DNA, proteins, etc.).
Graphene oxide (GO) has gained widespread attention in several research fields, particularly in antibacterial applications. A review entitled "Antibacterial Applications of Graphene Oxides: Structure-Activity Relationships, Molecular Initiating Events and Biosafety," published as the cover article of Science Bulletin 2018(2) issue, deliberated the structure-activity relationships (SARs) involved in GO-induced bacterial killing, molecular initiating events (MIEs) and biosafety of antibacterial applications.
The corresponding authors are Ruibin Li at the School for Radiation Medicine & Interdisciplinary Sciences - Soochow University, and Lingwen Zeng from the Guangzhou Institute of Biomedicine and Health at the Chinese Academy of Sciences.
GO has an exclusive two-dimensional (2D) honeycombed hydrophobic plane structure and hydrophilic groups, including carboxylic (-COOH) and hydroxyl (-OH) groups on its edge, which define its superior antibacterial activity. Among these antibacterial mechanisms, this review summarized the interactions between bacterial membranes and GO; looking specifically at the primary role of MIEs. These roles included mechanical destruction of membranes, redox reactions with biomolecules and catalysis of extracellular metabolites.
The review also talked in in detail about the physicochemical effect of GO on the bacterial membrane - phospholipid peroxidation, lipid extraction, the wrapping and trapping effect, insertion, and free radicals induced by GO.
Moreover, this review not only deliberated about the effect of shape, size, and surface functionality on the antibacterial activity to elaborate the SARs but also abridged the antibacterial nanoproducts that can be used for environmental, biomedical, and food engineering applications. Stress was also made on the biosafety of GO when used in the biomedical domain, considering that direct exposure of GO-based antibacterial agents to human cells may trigger risky detrimental effects. Thus, one must be very alert to the escape and release of GO into blood while employing GO-coated biomedical devices.
Lastly, the review has stated the future viewpoint and mentioned the difficulties of using GO as a novel nano-antibacterial agent, such as comprehending the interactions occurring at GO-bacteria interfaces, the investigation of GO-based nanocomposites to realize synergistic antibacterial effects, and the immobilization of GO for antibacterial use.