Giovanni De Bellis

Graphite Nanoplatelets and Caenorhabditis elegans: Insights from an in Vivo Model

We evaluated the toxicity of graphite nanoplatelets (GNPs) in the model organism Caenorhabditis elegans. The GNPs resulted nontoxic by measuring longevity as well as reproductive capability end points. An imaging technique based on Fourier transform infrared spectroscopy (FT-IR) mapping was also developed to analyze the GNPs spatial distribution inside the nematodes. Conflicting reports on the in vitro antimicrobial properties of graphene-based nanomaterials prompted us to challenge the host-pathogen system C. elegans-Pseudomonas aeruginosa to assess these findings through an in vivo model.

Zinc oxide microrods and nanorods: Different antibacterial activity and their mode of action against Gram-positive bacteria

The development of antibiotic resistance among pathogenic bacteria combined with increased implant-associated infections have determined a great interest towards new bactericidal materials containing various organic and inorganic substances. Among them, zinc oxide (ZnO) derived materials have received considerable attention due to their unique antibacterial, antifungal, and UV filtering properties as well as high catalytic and photochemical activities. In the present work, we investigate the antimicrobial properties against two Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis) of ZnO microrods (MRs) and nanorods (NRs), produced in bulk quantities through simple and inexpensive methods. We demonstrate that the antimicrobial effect is strongly dependent on the rod size and dose. Scanning electron microscopy analysis revealed that the two investigated microbial types interact differently with the ZnO-MRs and NRs due to their different morphology. This resulted in different outcomes as reported by their respective Colony Forming Unit (CFU) capabilities. Moreover, Fourier Transform Infrared (FT-IR) spectroscopy revealed that changes in cell outer structures, i.e. membrane and exopolysaccharides (EPS), produced by the interaction with the ZnO structures, are responsible for the antimicrobial mechanism without the accumulation of reactive oxygen species. This was further strengthened by the increased survival observed in the case of bacterial cells treated in the presence of an osmotic support, like glycerol. In addition, Inductively Coupled Plasma Mass Spectrometry (ICP-MS) analysis showed that reduced cell viability is not strictly correlated to increased zinc ion release in the suspension. We then concluded that ZnO-NRs have a superior antimicrobial effect against both S. aureus and B. subtilis at much lower doses when compared to ZnO-MRs. This is mainly due to the smaller diameter of the NRs, which promotes surface damaging and protein alteration of the cell wall. Finally, the lack of toxicity and the antimicrobial properties of ZnO-NRs versus S. aureus, validated in vivo using the nematode Caenorhabditis elegans as host infection model, confirm the promising exploitation of ZnO-NRs in biomedical applications.

Synthesis and characterization of ZnO nanorods with a narrow size distribution

The development of novel materials for energy harvesting applications or strain sensing has generated great interest towards zinc oxide (ZnO) nanostructures, and in particular towards the synthesis of ZnO nanowires or nanorods with well controlled morphology and properties. The high-yield mass production of such nanostructures by catalyst-free methods is a crucial aspect to enable a cost-effective large-scale development of new ZnO-based piezoelectric devices and materials. In the present work, we propose a method for the mass-production of high-purity ZnO-nanorods with a uniform size distribution, based on the combination of thermal decomposition of zinc acetate dihydrate and probe sonication in acetone. The quality of the produced ZnO nanorods is assessed through multi-technique characterization using field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and photo-luminescence spectroscopy (PL). The adopted synthesis method is simple, cost effective and feasible for large-scale production. Various process parameters such as precursor amount and growth time have been found to play an important role in controlling the formation of the as grown nanostructures with high uniformity in size and morphology. Size distribution curves were employed to depict the effect of various process parameters for tailoring the morphology, homogeneity and aspect ratio of the nanorods. Our results reveal that the high crystallographic quality of ZnO nanorods grown by a long-time thermal decomposition method is not affected by probe sonication, which is proposed as a post-synthesis step necessary to produce ZnO nanorod powder with a uniform distribution of diameters and lengths.

Inhibition of microbial growth by carbon nanotube networks.

In the last years carbon nanotubes have attracted increasing attention for their potential applications in the biomedical field as diagnostic and therapeutic nano tools. Here we investigate the antimicrobial activity of different fully characterized carbon nanotube types (single walled, double walled and multi walled) on representative pathogen species: Gram-positive Staphylococcus aureus, Gram-negative Pseudomonas aeruginosa and the opportunistic fungus Candida albicans. Our results show that all the carbon nanotube types possess a highly significant antimicrobial capacity, even though they have a colony forming unit capacity and induction of oxidative stress in all the microbial species to a different extent. Moreover, scanning electron microscopy analysis revealed that the microbial cells were wrapped or entrapped by carbon nanotube networks. Our data taken together suggest that the reduced capacity of microbial cells to forming colonies and their oxidative response could be related to the cellular stress induced by the interactions of pathogens with the CNT network.

Electromagnetic and Dynamic Mechanical Properties of Epoxy and Vinylester-Based Composites Filled with Graphene Nanoplatelets

Development of epoxy or epoxy-based vinyl ester composites with improved mechanical and electromagnetic properties, filled with carbon-based nanomaterials, is of crucial interest for use in aerospace applications as radar absorbing materials at radio frequency. Numerous studies have highlighted the fact that the effective functional properties of this class of polymer composites are strongly dependent on the production process, which affects the dispersion of the nanofiller in the polymer matrix and the formation of micro-sized aggregations, degrading the final properties of the composite. The assessment of the presence of nanofiller aggregation in a composite through microscopy investigations is quite inefficient in the case of large scale applications, and in general provides local information about the aggregation state of the nanofiller rather than an effective representation of the degradation of the functional properties of the composite due to the presence of the aggregates. In this paper, we investigate the mechanical, electrical, and electromagnetic properties of thermosetting polymer composites filled with graphene nanoplatelets (GNPs). Moreover, we propose a novel approach based on measurements of the dielectric permittivity of the composite in the 8–12 GHz range in order to assess the presence of nanofiller aggregates and to estimate their average size and dimensions.

Nitrogen-doped graphene films from chemical vapor deposition of pyridine: Influence of process parameters on the electrical and optical properties

Summary Graphene films were produced by chemical vapor deposition (CVD) of pyridine on copper substrates. Pyridine-CVD is expected to lead to doped graphene by the insertion of nitrogen atoms in the growing sp2 carbon lattice, possibly improving the properties of graphene as a transparent conductive film. We here report on the influence that the CVD parameters (i.e., temperature and gas flow) have on the morphology, transmittance, and electrical conductivity of the graphene films grown with pyridine. A temperature range between 930 and 1070 °C was explored and the results were compared to those of pristine graphene grown by ethanol-CVD under the same process conditions. The films were characterized by atomic force microscopy, Raman and X-ray photoemission spectroscopy. The optical transmittance and electrical conductivity of the films were measured to evaluate their performance as transparent conductive electrodes. Graphene films grown by pyridine reached an electrical conductivity of 14.3 × 105 S/m. Such a high conductivity seems to be associated with the electronic doping induced by substitutional nitrogen atoms. In particular, at 930 °C the nitrogen/carbon ratio of pyridine-grown graphene reaches 3%, and its electrical conductivity is 40% higher than that of pristine graphene grown from ethanol-CVD.

Zinc Oxide Nanorods-Decorated Graphene Nanoplatelets: A Promising Antimicrobial Agent against the Cariogenic Bacterium Streptococcus mutans

Nanomaterials are revolutionizing the field of medicine to improve the quality of life due to the myriad of applications stemming from their unique properties, including the antimicrobial activity against pathogens. In this study, the antimicrobial and antibiofilm properties of a novel nanomaterial composed by zinc oxide nanorods-decorated graphene nanoplatelets (ZNGs) are investigated. ZNGs were produced by hydrothermal method and characterized through field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) techniques. The antimicrobial activity of ZNGs was evaluated against Streptococcus mutans, the main bacteriological agent in the etiology of dental caries. Cell viability assay demonstrated that ZNGs exerted a strikingly high killing effect on S. mutans cells in a dose-dependent manner. Moreover, FE-SEM analysis revealed relevant mechanical damages exerted by ZNGs at the cell surface of this dental pathogen rather than reactive oxygen species (ROS) generation. In addition, inductively coupled plasma mass spectrometry (ICP-MS) measurements showed negligible zinc dissolution, demonstrating that zinc ion release in the suspension is not associated with the high cell mortality rate. Finally, our data indicated that also S. mutans biofilm formation was affected by the presence of graphene-zinc oxide (ZnO) based material, as witnessed by the safranin staining and growth curve analysis. Therefore, ZNGs can be a remarkable nanobactericide against one of the main dental pathogens. The potential applications in dental care and therapy are very promising.

Electro-Mechanical Properties of Multilayer Graphene-Based Polymeric Composite Obtained through a Capillary Rise Method

A new sensor made of a vinyl-ester polymer composite filled with multilayer graphene nanoplatelets (MLG) is produced through an innovative capillary rise method for application in strain sensing and structural health monitoring. The new sensor is characterized by high stability of the piezoresistive response under quasi-static consecutive loading/unloading cycles and monotonic tests. This is due to the peculiarity of the fabrication process that ensures a smooth and clean surface of the sensor, without the presence of filler agglomerates acting as micro- or macro-sized defects in the composite.

Evaluation of the antibacterial power and biocompatibility of zinc oxide nanorods decorated graphene nanoplatelets: new perspectives for antibiodeteriorative approaches

BackgroundNanotechnologies are currently revolutionizing the world around us, improving the quality of our lives thanks to a multitude of applications in several areas including the environmental preservation, with the biodeterioration phenomenon representing one of the major concerns.ResultsIn this study, an innovative nanomaterial consisting of graphene nanoplatelets decorated by zinc oxide nanorods (ZNGs) was tested for the ability to inhibit two different pathogens belonging to bacterial genera frequently associated with nosocomial infections as well as biodeterioration phenomenon: the Gram-positive Staphylococcus aureus and the Gram-negative Pseudomonas aeruginosa. A time- and dose-dependent bactericidal effect in cell viability was highlighted against both bacteria, demonstrating a strong antimicrobial potential of ZNGs. Furthermore, the analysis of bacterial surfaces through Field emission scanning electron microscopy (FESEM) revealed ZNGs mechanical interaction at cell wall level. ZNGs induced in those bacteria deep physical damages not compatible with life as a result of nanoneedle-like action of this nanomaterial together with its nanoblade effect. Cell injuries were confirmed by Fourier transform infrared spectroscopy, revealing that ZNGs antimicrobial effect was related to protein and phospholipid changes as well as a decrease in extracellular polymeric substances; this was also supported by a reduction in biofilm formation of both bacteria. The antibacterial properties of ZNGs applied on building-related materials make them a promising tool for the conservation of indoor/outdoor surfaces. Finally, ZNGs nanotoxicity was assessed in vivo by exploiting the soil free living nematode Caenorhabditis elegans. Notably, no harmful effects of ZNGs on larval development, lifespan, fertility as well as neuromuscular functionality were highlighted in this excellent model for environmental nanotoxicology.ConclusionsOverall, ZNGs represent a promising candidate for developing biocompatible materials that can be exploitable in antimicrobial applications without releasing toxic compounds, harmful to the environment.

Electromechanical modeling of GNP nanocomposites for stress sensors applications

Graphite nanoplatelets (GNPs) can be included in very low weight percentages in a polymer matrix to create new lightweight nanocomposites with desired electromechanical properties, for application in strain sensors. The development of simulation models for the prediction of the electromechanical characteristics of such composites is very important for design and performance optimization purposes. In this study we propose an electromechanical model for the prediction of the response of a strain sensor made of GNP-filled composite. The developed simulation approach is based on the tunneling-percolation model of the electrical transport in the composite, and on the experimental characterization of the dc conductivity of GNPs and GNP-filled composites at different concentrations, produced in the CNIS Labs of Sapienza University.