Don't forget about nanosecurity!
Once again about the safety of nanomaterials in general and graphene in particular
At the same time, there were many concerns related to the assumptions about the possible harmful effects of graphene materials on human health and the environment. Most of all, researchers were interested in the question of the toxicity of graphene materials in relation to the microworld of bacteria.
To clarify the situation, the Institute of Industrial Technology (Singapore) compared the antibacterial activity of graphite, graphite oxide (the same graphite whose surface is oxidized by the action of a mixture of strong acids), graphene oxide (a semi-product of the standard method for producing graphene) and reduced graphene oxide when acting on E. coli.
It turned out that both graphene materials killed much more bacteria than materials based on classical graphite, and graphene oxide turned out to be a clear contender for the first prize (see the graph from the article in ACS Nano – VM). It is also worth noting that the graphene oxide particles had the smallest size (the larger size of the reduced graphene particles is most likely due to the higher degree of aggregation of individual flakes), which was found out using the method of dynamic light scattering.
Unfortunately, due to the difference in the properties of the surface, the aggregate state and even the dimension of the elementary particles that make up large aggregates, it will not be possible to draw any unambiguous conclusions about the prevalence of a single factor (and in fact it is possible to consider combinations of various factors).
However, according to scientists, it is the small size of graphene oxide particles that may be the main indicator that provides bacterial lethality. After studying the effects of using these materials against bacteria using scanning electron microscopy, the authors found that individual E. coli cells were literally wrapped in layers of graphene oxide. At the same time, in the case of reduced graphene oxide, Escherichia coli cells were embedded in the structure of the overgrown aggregates (see microphotography). The same mechanism of cell capture by aggregates is also characteristic of graphite materials.
On the left – graphene oxide kills E. coli by wrapping around it. On the right – reduced graphene oxide does the same thing, capturing bacteria by growing aggregates (ACS microphoto).
Why does individual wrapping kill more bacteria than the capture of cells by aggregates? Scientists seriously believe that direct contact of the cell surface with graphene causes stress of the cell membrane, leading to irreversible damage. This cannot be called an explanation in any way: what kind of stress, why does carbon cause it, why is the contact when wrapping better than when embedding? It's like saying: the sun warms because it glows; there is some truth in this, but does it really explain anything? Rather, it is possible to make an assumption about the different activity of materials in terms of grams, and then everything falls into place. It can also be assumed that the chemical properties of the graphene oxide surface play an important role: together with the greater efficiency of the "winding" (including per gram of material), this can give a significant cumulative effect. But all this is just speculation…
In addition, the Singaporeans tried to study the chemical mechanisms that could be involved in the destruction of bacteria. As it turned out, in the case of E. coli, when the cell membrane comes into contact with the surface of graphite and reduced graphene oxide, glutathione (an important cellular antioxidant) is oxidized. According to the researchers, there is a certain probability that these structures serve as a kind of conducting bridges that remove electrons from glutathione molecules and transfer them to the environment (there is always an oxidizer in it). Apparently, we should conclude that the oxidation of a natural antioxidant dramatically reduces the natural viability of bacteria.
And what's in the dry residue? Yes, the same thing. We were once again clearly demonstrated that nanomaterials, even based on "harmless" carbon, can harbor many unexpected dangers for living cells, that is, for you and me, and for the entire environment. They repeated once again that it is impossible to install "nanocarbon" Petrik filters in kindergartens at the behest of corrupt officials-in-power, without knowing exactly how nanoparticles trapped in water will behave inside the body.
Read the report on the work done in the journal ACS Nano (Shaobin Liu et al., Antibacterial Activity of Graphite, Graphite Oxide, Graphene Oxide, and Reduced Graphene Oxide: Membrane and Oxidative Stress).
Prepared based on the materials of A*STAR Research, Functional materials: Two ways to kill.
Portal "Eternal youth" http://vechnayamolodost.ru31.08.2012