The development of new pharmacological strategies that evade bacterial resistance has become a compelling worldwide challenge. Graphene oxide (GO) can represent the nanotechnology answer being economical and easy to produce and to degrade and having multitarget specificity against bacteria. Several groups tried to define the interaction between GO sheets and human pathogens. Unfortunately, controversial results from inhibition to bacterial growth enhancement have been reported. The main difference among all experimental evidence relies on the environmental conditions adopted to study the bacteria−GO interaction. Indeed GO, stable in deionized water, undergoes a rapid and salt-specific DLVO-like aggregation that influences antimicrobial effects. Considering this phenomenon, the interaction of bacteria with GO aggregates having different sizes, morphologies, and surface potential can create a complex scenario that explains the contrasting results reported so far. In this article, we demonstrate that by modulating the GO stability in solution, the antibacterial or growth enhancement effect can be controlled on S. aureus and E. coli. GO at low concentration cuts microorganism membranes and at high concentration forms complexes with pathogens and inhibits or enhances bacterial growth in a surface potential-dependent manner. With the framework defined in this study, the clinical application of GO gets closer, and controversial results in literature can be explained.

Standing out as the new wonder bidimensional material, graphene oxide (GO) has aroused an exceptional interest in biomedical research by holding promise for being the antibacterial of future. First, GO possesses a specific interaction with microorganisms combined with a mild toxicity for human cells. Additionally, its antibacterial action seems to be directed to multiple targets in pathogens, causing both membranes mechanical injury and oxidative stress. Lastly, compared to other carbon materials, GO has easy and low-cost processing and is environment-friendly. This remarkable specificity and multi-targeting antibacterial activity come at a time when antibiotic resistance represents the major health challenge. Unfortunately, a comprehensive framework to understand how to effectively utilize this material against microorganisms is still lacking. In the last decade, several groups tried to define the mechanisms of interaction between GO flakes and pathogens but conflicting results have been reported. This review is focused on all the contradictions of GO antimicrobial properties in solution. Flake size, incubation protocol, time of exposure and species considered are examples of factors influencing results. These parameters will be summarized and analyzed with the aim of defining the causes of contradictions, to allow fast GO clinical application.

GO flakes, able to disrupt the erythrocyte plasma membrane, greatly reduce their haemolytic activity after interacting with plasma proteins. Haemolysis activity increases inversely to the GO flakes size.

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