Interactions of airborne graphene oxides with the sexual reproduction of a model plant: When production impurities matter.

The increasing use of graphene-related materials (GRMs) in everyday-life products raises concerns for their possible release into the environment and consequent impact on organisms. GRMs have widely varying effects on plants and, according to recent evidences, graphene oxide (GO) has the potential to interfere with the sexual reproduction owing to its acidic properties and production residues. Here, stigmas of the model plant Cucurbita pepo (summer squash) were subjected to simulated dry depositions of GO and GO purified from production residues (PGO). Stigmas were then hand-pollinated and GRM deposition was checked by ESEM and confocal microscopy. Analysis of stigma integrity, pH homeostasis and pollen-stigma interactions did not reveal negative effects. Fruit and seed production were not affected, but GO depositions of 22.1 ± 7.2 ng mm-2 affected the normal development of seeds, decreasing seed dimensions, seed germination and germination speed. The elemental analysis revealed that GO has significant quantities of production residues, such as strong acids and oxidants, while PGO has only traces, which justifies the differences observed in the effects caused by the two materials. Our results show that GO depositions of up to 11.1 ± 3.6 ng mm-2, which fall within the variation range of total dry particulate matter depositions reported in the literature, are safe for reproduction of C. pepo. This is the first "safety" limit ever recorded for depositions of "out-of-the-box" GO concerning the reproduction of a seed plant. If confirmed for wind-pollinated species, it might be considered for policymaking of GRMs emissions in the air.

Is airborne graphene oxide a possible hazard for the sexual reproduction of wind-pollinated plants?

Products containing graphene-related materials (GRMs) are becoming increasingly common, allowing GRM nanoparticles (NPs) to enter the environment during their life cycle. Thanks to their lightness and bidimensional geometry, GRM NPs can be easily dispersed in the air and travel very long distances. The flowers of wind-pollinated plants may be exposed to airborne GRMs, being apt to intercept pollen from the air and, inevitably, other airborne particles. Here, stigmas of four wind-pollinated plants (Corylus avellana, common hazel; Juglans regia, walnut; Quercus ilex, holm oak; Zea mays, maize) were exposed to airborne graphene oxide (GO) and GO purified from production residues (PGO) at a concentration of 3.7 ng m-3. Subsequently, the stigmas were pollinated and the adhesion of GOs and their effects on stigma integrity and pollen-stigma interaction were examined. The effect of GO NPs in presence of liquid water on the stigma of C. avellana was also investigated. GOs NPs were intercepted by all species, but their effect varied among them. GO reduced pollen adhesion in J. regia and Q. ilex, whereas pollen germination was unaffected in all four species. The presence of a film of water neither completely removed GO NPs from the stigma, nor it enhanced the toxic effect of GO acidity. PGO never affected pollen-stigma interaction, indicating that the phytotoxic substances used for the production of GO, still in traces in commercial GO, are the main cause of GO toxicity. These results reconfirm the need to verify GRMs effects also on key biological processes beside single model organisms.

Longitudinal cutting of pure and doped carbon nanotubes to form graphitic nanoribbons using metal clusters as nanoscalpels.

We report the use of transition metal nanoparticles (Ni or Co) to longitudinally cut open multiwalled carbon nanotubes in order to create graphitic nanoribbons. The process consists of catalytic hydrogenation of carbon, in which the metal particles cut sp(2) hybridized carbon atoms along nanotubes that results in the liberation of hydrocarbon species. Observations reveal the presence of unzipped nanotubes that were cut by the nanoparticles. We also report the presence of partially open carbon nanotubes, which have been predicted to have novel magnetoresistance properties.(1) The nanoribbons produced are typically 15-40 nm wide and 100-500 nm long. This method offers an alternative approach for making graphene nanoribbons, compared to the chemical methods reported recently in the literature.