Three antimicrobial nanoparticle types (AMNP0, AMNP1, and AMNP2) produced using the Tesima TM thermal plasma technology were investigated and their compositions were determined using a combination of analytical methods. Scanning electron micrographs provided the morphology of these particles with observed sizes ranging from 10 to 50 nm, whilst FTIR spectra confirmed the absence of polar bonds and organic impurities, and strong Raman active vibrational bands at ca. 1604 and 1311 cm −1 ascribed to C-C vibrational motions were observed. Carbon signals that resonated at δ C 126 ppm in the solid state NMR spectra confirmed that sp 2 hybridised carbons were present in high concentration in two of the nanoparticle types (AMNP1 and AMNP2). X-ray powder diffraction suggested that AMNP0 contains single phase Tungsten carbide (WC) in a high state of purity and multiple phases of WC/WC 1-x were identified in both AMNP1 and AMNP2. Finally, X-ray photoelectron spectral (XPS) analyses revealed and quantified the elemental ratios in these composite formulations. Nanomaterials 2017, 7, 152 2 of 16 have been a popular field, especially since the SARS (Severe acute respiratory syndrome) outbreak in 2003. The continuation of growing numbers of infectious diseases in hospitals, [17] propagation of pathogens, and their resistance against conventional antibiotics [18] have significantly raised global concern. Therefore using nanomaterials as antibacterials complementary to antibiotics is highly promising and is gaining a large interest, as they may fill the gaps where antibiotics frequently fail [19] . The activity of a widening spectrum of engineered metal/metal-oxide nanoparticles which can counter a specific range of oral pathogens associated with peri-implantitis has been investigated [20] . The findings assisted in the development of novel and innovative antimicrobial agents in an era of ever-increasing antimicrobial resistance. The potential of using nanoparticles as antimicrobial agents raised concerns about the possibility of nanoparticle toxicity on the central nervous system (CNS) [21] [22] [23] . In vivo investigation using hippocampus cells in young rats suggested an interactive connection between nano ZnO/Ag/CuO and the effectiveness of learning ability and the flexibility of cognition [21, [24] [25] [26] . Nevertheless, incremental nano-dosages increased the excitability in rat CA1 pyramidal neurons and confirmed a safety threshold of 0.05 wt % of injection suspension, which has provided an insight regarding the relative toxicity concern over the use of nanoparticles in biomedical engineering [27] [28] [29] . These findings proved the novelty of antimicrobial nanoparticles (AMNP) in a cost-effective fashion for inhibiting microbial growth, which may bring major changes in policy and new regulations on the wider uses of nanoparticles in biomedical healthcare [7, 16, 30] . AMNP derivatives were synthesized in a previous work with a stable efficacy (99.99% killing rates) in order to counteract a range of super bugs (i.e., E. coli, MRSA) and a range of viruses (SARS, H5N1, and Noroviruses) [30, 31] . As well as the accumulative biological results obtained from AMNP powder suspensions, AMNP doped polymer fibres produced using pressurized gyration [32] were recently found to inhibit the growth of P. aeruginosa, a Gram-negative bacterial species that is commonly found in hospitals [33] . Although, AMNP nanoparticles exhibit antimicrobial functions, their chemical and particle characterisations are not documented. Furthermore, how they interact with microbes has not been directly investigated. Most known antibacterial nanomaterials interact electrostatically with the bacterial membrane causing membrane disruption [19, 34] . Consequently, free radicals are produced and instigate secondary membrane damage causing protein malfunction and DNA destruction [3] . Other antimicrobial nanomaterials such as nitric oxide matrices involve photoactivation with RNS (Reactive oxygen and nitrogen species) [35] or polycationic nanomaterials induce signal secretion to promote programmed cell death [36] . In this paper, we report chemical analyses obtained from these AMNP series (AMNP0, AMNP1, and AMNP2) using a range of techniques including FTIR/Raman spectroscopy, Solid state Carbon-13 Nuclear Magnetic Resonance spectroscopy, Powder X-ray Diffraction and X-ray Photoelectron Spectroscopy [37] . Through the chemical investigation, we found that C, W, Ag, Cu, and O are the main elements contained in these AMNP formulations, and we also identified several phases present in these series (i.e., WC, WC 1−x , CuO). By understanding the lattice structures and chemistry of these antimicrobial nanoparticle composites, we hope to identify biological surface-interactions between these ultra-small particles and the microbes. This will help in studying the reaction mechanisms involved in target bacterium or viruses, and will also help to design and create custom-made antimicrobial formulations in the future. Results and Discussion The surface morphologies of the AMNP derivatives were studied using SEM. Figure 1a -c show the representative SEM images of AMNP0, AMNP1, and AMNP2, respectively. As shown in Figure 1a , the SEM image of the examined AMNP0 particles indicates that the sample was quite uniformly distributed. Although a large differentiation in their particle sizes were measured (50-500 nm), we Nanomaterials 2017, 7, 152 3 of 16 were able to observe the apparent hexagonal units' presence in these particles, which were later confirmed to be the P6m2 tungsten carbide in our XRD study. In contrast, both SEM images of AMNP1 ( Figure 1b) and AMNP2 (Figure 1c ) showed a significant decrease in their particle sizes (10-30 nm). Both AMNP1 and AMNP2 were found to be heavily agglomerated and highly charged due to the nonconductive nature (i.e., non-metallic) of the samples. As a consequence, capturing good SEM images at higher resolution using accelerating voltage was difficult. Nanomaterials 2017, 7, 152 3 of 16 confirmed to be the P6m2 tungsten carbide in our XRD study. In contrast, both SEM images of AMNP1 ( Figure 1b ) and AMNP2 (Figure 1c ) showed a significant decrease in their particle sizes (10-30 nm). Both AMNP1 and AMNP2 were found to be heavily agglomerated and highly charged due to the nonconductive nature (i.e., non-metallic) of the samples. As a consequence, capturing good SEM images at higher resolution using accelerating voltage was difficult.
Output: Characterisation of the Chemical Composition and Structural Features of Novel Antimicrobial Nanoparticles