Graphene Oxide (GO) is a well known graphene derivative of the chemical graphene-family nanomaterials (GFNs), made from graphite oxide. The difference between graphite oxide and GO are on their structures with chemical composition remains alike. GO is a single-layered material made of carbon, hydrogen and oxygen molecules. The nanoparticles are used in nanoelectric devices, batteries, antibacterials, biosensors, cell imaging, drug delivery, and tissue engineering. GO tends to be an electrical insulator rather than a conductor. Nevertheless, GO can be reduced to form reduced graphene oxide (rGO) to retrieve its hexagonal lattice structure and produce graphene-like sheets by removing a large portion of oxygen groups to closely resemble graphene.
In cellular imaging, functionalized GO can be used as fluorescence and photoluminescent. Squaraine dyes that had been loaded inside mesoporous silica nanoparticles and ultrathin GO sheets wrapped the NPs. The loaded dye was covered from the nucleophilic attack1.
Biological Properties of Graphene and GO
A study published in 2013 reported that small graphene sheets tend to penetrate into the cell via spontaneous piercing at their sharpest hydrophobic corner2. The physicochemical properties of 2D materials, such as structure, shape, size, surface functionality, concentration, and aggregation state have an essential impact on cellular behavior. Graphene has the potential to cause cell damage during the penetration of cell membranes because of the sharp edges. Its aggregation can lead to cytotoxicity. Graphene at the nanoscale, when <100 nm, results in cytotoxicity, inflammation, and even genotoxicity. Graphene, being nonbiodegradable (except FGO), presents serious concerns for potential toxicity, immune response, and environmental hazards. Graphene with functionalized groups (i.e., GO, FGO such as the amine group, and rGO) is easily internalized by cells (especially in nano sizes), in addition to causing more irregular cell membrane perturbation. GO and derivatives are cytocompatible in vitro and in vivo. GO's sharp edges that damage the cell membrane, are also used for bacterial cell mortality via the membrane stress mechanism. GO and its derivatives have specific antibacterial properties. GOBMs have antioxidant properties. GO biodegradation is via oxidative attack through hydrogen peroxide and horseradish peroxidase3. GO toxicity depends on flake composition, chemical functionalization and dimensions.
Magnetic Field
Graphene is intrinsically nonmagnetic. Magnetic hysteresis loop shows that GO is ferromagnetic. Photo-thermal moderately reduced graphene oxide (M-rGO) gradually has paramagnetic behavior at room temperature4. Some techniques can make GO to be ferromagnetism with certain temperature.
Vaccines with GO
GO can be used as vaccine adjuvant and nanocarrier. It is used as a vaccine adjuvant for immunotherapy using urease B (Ure B) as the model antigen. Polyethylene glycol (PEG) and various types of polyethylenimine (PEI) were used as coating polymers. Certain dual-polymer modified GOs (GO–PEG–PEI) can act as a positive modulator to promote the maturation of dendritic cells (DCs) and enhance their cytokine secretion through the activation of multiple toll-like receptor (TLR) pathways while showing low toxicity5. GO loads and deliver antigen and shows the potentiality of activating the immune system. GO aggregates in biological liquid and induces cell death, and it also exhibits poor biosolubility and biocompatibility. Many studies aim at various surface modification protocols have been done to integrate aqueous compatible substances with GO to effectively improve its biocompatibility6. Another study reported that PEI-FGO nanoparticles showed high antigen-loading capacities and superior immunoenhancing properties for intranasal (i.n.) influenza vaccine7.
Other Applications
Researchers in 2014 reported a new class of remote-controlled release system by incorporating photoacid generator (PAG) into GO-capped mesoporous silica was designed for delivering drug payloads to cancer cells via photoinduced pH-jump activation8. Another study in 2012 used GO in photothermally sensitive poly(N-isopropylacrylamide)/GO nanocomposite hydrogels as remote light-controlled for liquid microvalves9. A 2019 study reported engineered magnetic graphene oxide (MGO) in the nanocomposite form of iron oxide nanoparticles (IO)-GO, for magnetic resonance imaging (MRI) applications10. Researchers in 2018 reported graphene materials to drive neuronal growth and regeneration in vivo, and the possibility of using graphene as a component of hybrid composites/multi-layer organic electronics devices. They showed the interaction of graphene with proteins and cell membranes at the nanoscale, and describing the physical mechanism(s) of charge transfer by which the various graphene materials can influence the excitability and physiology of neural cells11.
Even though there have been many studies and findings of GO and FGO, one needs to realize that a mass scale production for sensitive properties like GO and FGO need to be reviewed. Moreover for applications related with human inner cells or organs, publics need to be critical and make opened scientific discussions for the sake of present and next generations life.
Abbreviations
GO = graphene oxide
rGO = reduced graphene oxide
FGO = functionalized GO
GOBMs = GO-based materials
https://www.acsmaterial.com/blog-detail/graphene-oxide.html
https://www.pnas.org/content/110/30/12295
https://www.mdpi.com/2079-4991/11/5/1083/htm
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https://pubs.rsc.org/en/content/articlelanding/2016/nr/c5nr09208f#!divAbstract
https://www.sciencedirect.com/science/article/abs/pii/S1742706120303305
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