There is an urgent need to find alternative routes to control the spreading of antibiotics-resistant bacteria. Graphene and its water-soluble form graphene oxide (GO) were previously shown to be promising antibacterial agents. However, their antibacterial activity was relatively low and they show toxicity to human cells at high dose of usage. This study demonstrated a new strategy for significantly enhancing the antibacterial activity of graphene oxide. It showed that graphene oxide can kill 99% of bacteria when mixed with a human-friendly detergent in salt-reduced water. Further, the mixture of graphene oxide and Pluronic displays over 50% lower toxicity to human skin cells than the effect of graphene oxide alone. The developed strategy relies on the combination of two effects. The first effect is coming from the water itself. Bacteria inevitably undergo swelling when faced with salt-reduced water which puts a stress on bacterial envelope due to occurrence of microscopic damages. The second effect comes from pluronic; a bio-friendly polymer widely used in drug formulations and food applications. Pluronic increases the stability of graphene oxide in solution and also helps graphene oxide to interact with bacteria better by surrounding the bacterial cells more effectively. Water and detergents are undoubtedly the most common cleaning agents. This study may open the door for graphene oxide to be a widespread cleaning agent for fighting bacteria.
Karahan HE1,2, Wei L1, Goh K1, Wiraja C1, Liu Z1, Xu C1,3, Jiang R1, Wei J2, Chen Y1,4.[expand title=”Show Affiliations”]
- School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore, 637459, Singapore.
- Singapore Institute of Manufacturing Technology (SIMTech), Singapore, 638075, Singapore.
- NTU-Northwestern Institute of Nanomedicine, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798, Singapore.
- School of Chemical and Biomolecular Engineering, The University of Sydney, Sydney, 2006, Australia.[/expand]
Graphene oxide (GO) is promising in the fight against pathogenic bacteria. However, the antibacterial activity of pristine GO is relatively low and concern over human cytotoxicity further limits its potential. This study demonstrates a general approach to address both issues. The developed approach synergistically combines the water shock treatment (i.e., a sudden decrease in environmental salinity) and the use of a biocompatible block copolymer (Pluronic F-127) as a synergist co-agent. Hypoosmotic stress induced by water shock makes gram-negative pathogens more susceptible to GO. Pluronic forms highly stable nanoassemblies with GO (Pluronic-GO) that can populate around bacterial envelopes favoring the interactions between GO and bacteria. The antibacterial activity of GO at a low concentration (50 μg mL(-1) ) increases from <30% to virtually complete killing (>99%) when complemented with water shock and Pluronic (5 mg mL(-1) ) at ≈2-2.5 h of exposure. Results suggest that the enhanced dispersion of GO and the osmotic pressure generated on bacterial envelopes by polymers together potentiate GO. Pluronic also significantly suppresses the toxicity of GO toward human fibroblast cells. Fundamentally, the results highlight the crucial role of physicochemical milieu in the antibacterial activity of GO. The demonstrated strategy has potentials for daily-life bacterial disinfection applications, as hypotonic Pluronic-GO mixture is both safe and effective.
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