Dual functional nisin-multi-walled carbon nanotubes coated filters for bacterial capture and inactivation

Background

Removal of pathogens from water is one way to prevent waterborne illness. In this paper, we developed dual functional carbon nanotube (CNT) modified filters for bacterial capture and inactivation, utilizing multi-walled CNTs (MWCNTs) to coat on commercially available filters and making use of the exceptional adsorption property of CNTs to adsorb a natural antimicrobial peptide-nisin on it. Two types of MWCNTs with different outer layer diameters were used (MWCNTs1: <8 nm in diameter; MWCNTs2: 10–20 nm in diameter).

Results

The thickness of MWCNT layers, surface morphology, and surface hydrophobicity of both types of MWCNT coated filters were characterized. The MWCNT coating on filters significantly increased the surface hydrophobicity. The absorption of nisin and the capture of bacterial pathogens were correlated with increased surface hydrophobicity. The MWCNTs1 and MWCNTs2 filters with 1.5 mg MWCNTs loading captured 2.44 and 3.88 log of cells, respectively, from aqueous solutions containing a total of ~10⁶ CFU/mL cells. Nisin deposit at the amount of 0.5 mg on the surfaces of MWCNT filters significantly reduced the viability of captured B. anthracis cells by 95.71–97.19 %, and inhibited the metabolic activities of the captured cells by approximately 98.3 %.

Conclusions

The results demonstrated that the MWCNT-nisin filters achieved dual functions in bacterial pathogen capture and inhibition in one single filtration step, which is potentially applicable in removing undesired microorganisms from water sources and inhibiting captured Gram positive bacteria activities.

     

Nanoscale structure of organic matter could explain litter decomposition

Soil organic matter (SOM) turnover is crucial for soil quality and fertility in biogeochemical carbon cycle dynamics that can influence the fluxes of greenhouse gases. This research was focused to acquire deeper understanding of the mechanisms leading to decomposition of plant tissue and SOM persistence against both aerobic and anaerobic biodegradation. Decomposition rates of a various biomass types were studied conducting experiments in both aerobic and anaerobic environments. Different analytical approaches were applied in order to characterize biomass at chemical and physical levels. Combined statistical approaches were used to examine the relationships between carbon mineralization and chemical/physical characteristics. The obtained results revealed that degradation was significantly and negatively correlated with the micro-porosity surface (surface of pores of 0.3–1.5 nm of diameter). The multiple regressions performed by using partial least squares modelling enabled describing biomass biodegradability under either aerobic and anaerobic condition by using micro-porosity and aromatic-C content (assumed to be representative of lignin) as independent variables (R² = 0.97, R _cv ²  = 0.95 for aerobic condition; R² = 0.99, R _cv ²  = 0.98 for anaerobic condition, respectively). These results corroborate the hypothesis that plant tissues are physically protected from enzymatic attack by a microporous “sheath” that limits enzyme penetration into cell wall, and demonstrate the key role played by aromatic carbon, because of its chemical protection of the other cell wall polymers and its contribution to the three-dimensional (3D) cell wall structure.     

AFM Investigations of Cellulose Fibers in Bintje Potato (Solanum tuberosum L.) Cell Wall Fragments

Atomic force microscopy (AFM) has been used to image the cellulose networks in moist fragments of the cell walls of Bintje potato (Solanum tuberosum L.). The interfiber spacing in hydrated native cell wall fragments was found to be 26.2 nm. This value is consistent with published estimates of the contour length of xyloglucan cross-links determined by transmission electron microscopy (TEM) studies of cell walls. Sequential extraction of the pectin using CDTA and Na₂CO₃ led to shrinkage of the cell wall fragment and a reduction in interfiber spacing to 20.2 nm. Partial extraction of xyloglucan using 1 M KOH caused a small decrease in interfiber spacing to 19.5 nm. Finally, the almost complete removal of xyloglucan with 4 M KOH substantially reduced the interfiber spacing to 11 nm. The results are consistent with a model for the cell wall in which the cellulose–xyloglucan network is immersed in a swollen, hydrated pectin network.     

Strong Near-infrared Avalanche Photoluminescence from Ag Nanowire Arrays

Ag nanowire (NW) arrays with NW diameter d _NW?=?12–120 nm were electrodeposited in anodic aluminum oxide templates. Strong avalanche photoluminescence (PL) from Ag NW arrays with small d _NW were observed near 914 nm by using picosecond laser at the excitation wavelength 808 nm, which is originated from the plasmon-enhanced radiative intraband transitions. The peak PL intensity of the avalanche PL from the sample with small diameter d _NW?=?12 nm is about 10² times stronger than that of the linear PL from the sample with large diameter d _NW?=?120 nm. The opposite excitation polarization dependence and emission polarization distribution of the PL from Ag NW array with d _NW?=?12 nm and d _NW?=?120 nm were also observed.     

Thermal and chemical denaturation of Colocasia esculenta tuber agglutinin from α2β2 to unfolded state

The major tuber storage protein of Colocasia esculenta, is a monocot mannose-binding, widely used dietary lectin, containing two polypeptides of 12.0 and 12.4 kDa. By both gel filtration and dynamic light scattering at pH 7.2, the lectin has a α₂β₂ form of apparent molecular mass of 48.2 kDa and a hydrodynamic radius of 6.1 ± .2 nm; however, at pH 3, it migrates as αβ and has a reduced hydrodynamic radius of 4.6 ± .3 nm. Our circular dichroism spectroscopy studies show that the lectin retains approximately 100% of its secondary structure between pH 2–8, going down to ~90% for extreme acidic/alkaline conditions. The fluorescence emission maxima of 346 to 350 nm for pH 4 to 10 show that the tryptophan residues are relatively exposed. The unfolding is a simple two-state process, N₄ ? 4U, as seen in our denaturation scan profiles. These denaturation profiles, monitored separately by fluorescence, far-UV CD, and near-UV CD, are completely super imposable. Analyses of these profiles provide an estimate of several thermodynamic parameters at each guanidinium chloride concentration, including the melting temperature T_g, which is 346.9 K in 0 M, but lowers to 321.8 K in 3.6 M. Dimeric and tetrameric interfaces observed in the crystal structure for the same protein are used to rationalize solution data in some detail.     

Lubrication and load-bearing properties of human salivary pellicles adsorbed ex vivo on molecularly smooth substrata

In a series of Surface Force Balance experiments, material from human whole saliva was adsorbed to molecularly smooth mica substrata (to form an ‘adsorbed salivary film’). Measurements were taken of normal (load bearing, F _n) and shear (frictional, F _s*) forces between two interacting surfaces. One investigation involved a salivary film formed by overnight adsorption from undiluted, centrifuged saliva, with the adsorbed film rinsed with pure water before measurement. Measurements were taken under pure water and 70 mM NaNO₃. In a second investigation, a film was formed from and measured under a solution of 7% filtered saliva in 10 mM NaNO₃. F _n results for both systems showed purely repulsive layers, with an uncompressed thickness of 35–70 nm for the diluted saliva investigation and, prior to the application of shear, 11 nm for the rinsed system. F _s* was essentially proportional to F _n for all systems and independent of shear speed (in the range 100–2000 nm s^?1), with coefficients of friction  μ ～ 0.24 and μ ～ 0.46 for the unrinsed and rinsed systems, respectively. All properties of the rinsed system remained similar when the pure water measurement environment was changed to 70 mM NaNO₃. For all systems studied, shear gave rise to an approximately threefold increase in the range of normal forces, attributed to the ploughing up of adsorbed material during shear to form debris that stood proud of the adsorbed layer. The results provide a microscopic demonstration of the wear process for a salivary film under shear and may be of particular interest for understanding the implications for in vivo oral lubrication under conditions such as rinsing of the mouth cavity. The work is interpreted in light of earlier studies that showed a structural collapse and increase in friction for an adsorbed salivary film in an environment of low ionic strength.     

Regular Array in the Cell Wall of Lactobacillus fermenti as Revealed by Freeze-Etching and Negative Staining1

Freeze-etching of Lactobacillus fermenti F-4 (NCTC 7230) revealed that the outer layer of the cell wall was composed of a regular array in which parallel lines ran obliquely to the longitudinal axis of the cell with an average distance between the centers of about 9.6 nm and were intersected by thinner lines with an average periodicity of approximately 6.2 nm at an angle of about 75°. Occasionally the direction of the striation was discontinuously shifted near one end of the cell. Beneath the regular array the middle cell wall layer packed with granules and the smooth inner cell wall layer were discernible and the mesosomes were also visible in the cytoplasm. When the ultrastructure of isolated outer cell wall fragments was examined by negative staining, the regular array appeared to be composed of subunits, about 3.6 nm in diameter, which were arranged in a tetragonal pattern. The tetragonal array consisted of the subunits in rows in two directions at an angle of about 75° to each other. The average spacing between the rows was about 9.3 nm in one direction and 5.5 nm in the other direction.     

Structure of a self-assembled single nanotube of cyclo[(-d-Ala-l-Ala)4-]

Diameter and wall thickness of self-assembled peptide nanotube of cyclo[(-d-Ala-l-Ala)₄-] were characterised by molecular simulation. In order to verify the existence of peptide nanotube of cyclo[(-d-Ala-l-Ala)₄-], cyclo[(-d-Ala-l-Ala)₄-] was firstly synthesised through Fmoc solid-phase synthesis method and then self-assembled in trifluoroacetic acid. Based on the results of experiment, the single nanotube structure was further characterised by molecular dynamics (MD) employing the COMPASS force field. The results indicate that cyclo[(-d-Ala-l-Ala)₄-] is self-assembled into nanotube bundles of about 0.5 μm in diameter and 10 μm in length; the inner and outer diameter of the single nanotube is 8.5 and 15.9 Å, respectively, and the nanotube wall thickness is 3.3 Å.     

Exploring the structure and dynamics of nano-confined water molecules using molecular dynamics simulations

Confinement effects can lead to drastic changes in the structural and dynamical properties of water molecules. In this work, we have performed classical molecular dynamics simulations of endohedral fullerenes of type (H₂O)_n@C_m (n = 1, 12, 21, 62, 108 and m = 60, 180, 240, 500 and 720) to explore the effects of spherical confinement on water properties. It is shown that these confined water molecules can form distinct solvation pattern depending upon the available space inside the fullerene cavity. For the systems with smaller diameter, cage-like structure is predominant whereas bulk-like structure is observed for larger fullerenes. The orientational relaxation of these confined water molecules showed slower relaxation as the cavity diameter increases except for the (H₂O)₂₁@C₂₄₀. In this case, stable cage-like structure hinders the overall dynamics of the trapped water molecules. Finally, we have calculated the hydrogen bond lifetimes from the hydrogen bond time correlation functions and compared with that of bulk water.     

Fabrication and Optical Properties of Au-Coated Polystyrene Nanosphere Arrays with Controlled Gaps

Large area monolayer of self-assembled polystyrene sphere (PS) arrays were formed by an interface self-assembly method and the gap of PS was adjusted by O₂ plasma treatment (OPT). After different duration of OPT, the spacing between the PSs varied from 5 to 88 nm. Then, 20 nm Au film was deposited on the PS arrays by electron beam deposition. The absorption peaks of Au-coated PS array red-shifted obviously by changing the gap of PS. The new absorption peaks emerged when the gap of the PS decreased to about 20 nm. The surface plasmon resonance (SPR) was employed to explain the absorption proportion of this Au-PS structure. These micro-nano structures exhibit tunable SPR bands, which may be useful to the applications in some research fields, such as biosensing, single molecule detection, and novel optoelectronic devices.     

Probing the Diameter Limit of Single Walled Carbon Nanotubes in SWCNT: Fullerene Solar Cells

In this work, for the first time, the diameter limit of surfactant wrapped single walled carbon nanotubes (SWCNTs) in SWCNT:C₆₀ solar cells is determined through preparation of monochiral small and large diameter nanotube devices as well as those from polychiral mixtures. Through assignment of the different nanotube chiralities by photoluminescence and optical density measurements a diameter limit yielding 0% internal quantum efficiency (IQE) is determined. This work provides insights into the required net driving energy for SWCNT exciton dissociation onto C₆₀ and establishes a family of (n,m) species which can efficiently be utilized in polymer‐free SWCNT:C₆₀ solar cells. Using this approach the largest diameter nanotube with an IQE > 0% is found to be (8,6) with a diameter of 0.95 nm. Possible strategies to extend this diameter limit are then discussed.     

Titanium dioxide nanoparticles preferentially bind in subdomains IB,IIA of HSA and minor groove of DNA

Titanium dioxide nanoparticles (TiO₂-NPs) interaction with human serum albumin (HSA) and DNA was studied by UV–visible spectroscopy, spectrofluorescence, circular dichroism (CD), and transmission electron microscopy (TEM) to analyze the binding parameters and protein corona formation. TEM revealed protein corona formation on TiO₂-NPs surface due to adsorption of HSA. Intrinsic fluorescence quenching data suggested significant binding of TiO₂-NPs (avg. size 14.0 nm) with HSA. The Stern–Volmer constant (K_sv) was determined to be 7.6 × 10² M^?1 (r² = 0.98), whereas the binding constant (K_a) and number of binding sites (n) were assessed to be 5.82 × 10² M^?1 and 0.97, respectively. Synchronous fluorescence revealed an apparent decrease in fluorescence intensity with a red shift of 2 nm at Δλ = 15 nm and Δλ = 60 nm. UV–visible analysis also provided the binding constant values for TiO₂-NPs–HSA and TiO₂-NPs-DNA complexes as 2.8 × 10² M^?1 and 5.4 × 10³ M^?1. The CD data demonstrated loss in α-helicity of HSA and transformation into β-sheet, suggesting structural alterations by TiO₂-NPs. The docking analysis of TiO₂-NPs with HSA revealed its preferential binding with aromatic and non-aromatic amino acids in subdomain IIA and IB hydrophobic cavity of HSA. Also, the TiO₂-NPs docking revealed the selective binding with A-T bases in minor groove of DNA.     

Lysogeny among mycobacteria

Our investigations to detect naturally lysogenic strains of mycobacteria were limited to 1 strain ofMycobacterium smegmatis, 4 strains ofMycobacterium borstelense var.niacinogenes, and to 5 strains ofMycobacterium marinum (Syn:Mycobacterium balnei), all together 10 strains. They were chosen because as a sign of lysis they secrete a large quantity of cytoplasmatic components (nucleic acids proteins, amino acids etc.) into the fluid medium (for instance phosphate buffer), in which they are suspended. In a first series of experiments culture filtrates were tested on 84 strains of slowly and rapidly growingMycobacterium species as indicator strains. Using this method free phage particles were only found in the culture filtrate of 1 strain,Mycobacterium smegmatis SN 46, isolated from a patient with achalasia. Phage particles could not be found in the filtrates of the other 9 probably lysogenic strains. In a second series of experiments more closely related indicator strains were used. The 10 probably lysogenic strains were cultured in bovine serum or antiphage-antiserum containing medium and single selected colony cultures a small part of which showed sensitivity to the filtrates. The released and adapted phages, designated as B₂₄, B₃₀, B₃₂, B₃₃, B₃₄ and B₃₅ have a very narrow host range. The plaques are very small and turbid. On electron micrographs the temperate phages B₂₄, B₃₀ and B₃₅ exhibit the typical head-tail morphology. The head of the temperateborstelense var.niacinogenes phage B₃₀ is 45 nm in diameter, the tength of tail is about, 120nm. The average dimensions of the long head ofsmegmatis phage B₂₄ are 40 × 80 nm, the tail is about 160 nm long. The balnei phage B₃₅ is very similar morphologically to phage B₃₀. The head is about 50 nm in diameter, the length of tail about 160 nm. The phage sensitive variants are not “carrier” strains. Their phage sensitivity is not a stable property. After several culture passages in serum-free medium the variants regain their phage immunity completely and release phages like the lysogenic parent strains. The sensitive variants must therefore be considered to be also lysogenic. TheMycobacterium borstelense var.niacinogenes phages are serologically very related. Dedicated to Academician Ivan Málek on the occasion of his 60th birthday     

Extended “Adsorption–Insertion” Model: A New Insight into the Sodium Storage Mechanism of Hard Carbons

Hard carbons (HCs) are promising anodes of sodium‐ion batteries (SIBs) due to their high capacity, abundance, and low cost. However, the sodium storage mechanism of HCs remains unclear with no consensus in the literature. Here, based on the correlation between the microstructure and Na storage behavior of HCs synthesized over a wide pyrolysis temperature range of 600–2500 °C, an extended “adsorption–insertion” sodium storage mechanism is proposed. The microstructure of HCs can be divided into three types with different sodium storage mechanisms. The highly disordered carbon, with d₀₀₂ (above 0.40 nm) large enough for sodium ions to freely transfer in, has a “pseudo‐adsorption” sodium storage mechanism, contributing to sloping capacity above 0.1 V, together with other conventional “defects” (pores, edges, heteroatoms, etc.). The pseudo‐graphitic carbon (d‐spacing in 0.36–0.40 nm) contributes to the low‐potential (<0.1 V) plateau capacity through “interlayer insertion” mechanism, with a theoretical capacity of 279 mAh g^?1 for NaC₈ formation. The graphite‐like carbon with d₀₀₂ below 0.36 nm is inaccessible for sodium ion insertion. The extended “adsorption–insertion” model can accurately explain the dependence of the sodium storage behavior of HCs with different microstructures on the pyrolysis temperature and provides new insight into the design of HC anodes for SIBs.     

Speckled SiO2@Au Core–Shell Particles as Surface Enhanced Raman Scattering Probes

Silica particles of ~800 nm size were functionalized using 3-amino propyl triethoxysilane molecules on which gold particles (~20 nm size) were deposited. The resulting particles appeared to form speckled SiO₂@Au core–shell particles. The surface roughness, along with hot spots, due to nanogaps between the gold nanoparticles was responsible for the enhancement of the Raman signal of crystal violet molecules by ~3.2?×?10⁷ and by ~1.42?×?10⁸ of single-wall carbon nanotubes. It has also been observed that the electromagnetic excitation near surface plasmon resonance (SPR) of core–shell particles is more effective than off resonance SPR excitation.     

Calyptospora empristica n. sp. (Eimeriorina: Calyptosporidae) from the Liver of the Starhead Topminnow,Fundulus notti1

Oocysts of Calyptospora empristica n. sp., the second described species in its genus, are described from the freshwater starhead topminnow, Fundulus notti, in southern Mississippi. Oocysts are 22 μm in diameter with a wall about 20 nm thick and have no residuum, micropyle, or polar granule. Sporocysts are spheroid, 9 × 5 μm with a two-layered wall approximately 120 nm thick. They have an oblong apical opening at the anterior pole, a single ornamented sporopodium approximately 5.7 μm long at the posterior pole, and a residuum. An intermediate host, most likely the freshwater grass shrimp Palaemonetes kadiakensis, is probably required to complete the life cycle.     

Molecular simulation of shale gas adsorption and diffusion in inorganic nanopores

We studied the structural and dynamical properties of methane and ethane in montmorillonite (MMT) slit pore of sizes 10, 20 and 30 Å using grand canonical Monte Carlo and classical molecular dynamics (MD) simulations. The isotherm, at 298.15 K, is generated for pressures up to 60 bar. The molecules preferentially adsorb at the surface as indicated by the density profile. In case of methane, we observe only a single layer, at the pore wall, whose density increases with increasing pressure. However, ethane also displays a second layer, though of low density in case of pore widths 20 and 30 Å. In-plane self-diffusion coefficient, D_‖, of methane and ethane is of the order of 10^? 6 m²/s. At low pressure, D_‖ increases significantly with the pore size. However, D_‖ decreases rapidly with increasing pressure. Furthermore, the effect of pore size on D_‖ diminishes at high pressure. Ideal adsorbed solution theory is used to understand the adsorption behaviour of the binary mixture of methane (80%) and ethane (20%) at 298.15 K. Furthermore, we calculate the selectivity of the gases at various pressures of the mixture, and found high selectivity for ethane in MMT pores. However, selectivity of ethane decreases with increase in pressure or pore size.     

Alpha-Fe2O3 elicits diameter-dependent effects during exposure to an in vitro model of the human placenta

Iron oxide nanoparticles offer unique possibilities due to the change in their physico-chemical parameters when synthesized on the nanoscale (10^?9 m) compared to their bulk forms. While novel uses exist for these materials when synthesized as nanoparticles, their unintended effects on the human body and specifically during pregnancy remain ill defined. In this study, an iron oxide nanoparticle, α-Fe₂O₃, was employed and the potential toxicity due to exposure was assessed in the widely used model human placental cell line BeWo b30. These cells were grown as epithelia, and subsequently assessed for their epithelial integrity, reactive oxygen species production and cellular viability, ultrastructural and morphological disruption, and genotoxicity as a result of exposure to α-Fe₂O₃ nanoparticles. Transepithelial electrical resistance indicated that exposure to the large (50 and 78 nm), but not small (15 nm) diameter particles of α-Fe₂O₃ nanomaterial resulted in leakiness of the epithelium. Exposure to the large diameters of 50 and 78 nm resulted in increases in cell death and reactive oxygen species. Disruption of junctional integrity as monitored by immunolocalization of the tight junction protein ZO-1 was found to occur as a consequence of exposure to large diameter NPs. It was found that there was reduction in the number of microvilli responsible for increased surface area for nutrient absorption after exposing the epithelia to large diameter NPs. Finally, genotoxicity as assessed by DNA microarray and confirmed by QPCR indicated that the large diameter particles (78 nm) induce apoptosis in these cells. These data indicate that large (50 and 78 nm), but not small (15 nm) α-Fe₂O₃ nanoparticles disrupt the barrier function of this epithelium as assessed by in vitro analysis.     

Investigations on the Thermal Stability of Fullerene-Based (Ag-C<Subscript>70</Subscript>) Nanocomposite Thin Films

Fullerene-based bi-functional nanocomposite thin film (Ag nanoparticles embedded in fullerene C₇₀ matrix) is synthesized by thermal co-deposition method. Thermal stability of Ag-C₇₀ nanocomposite is investigated by annealing the nanocomposite thin film at different temperatures from 80 to 350 °C for 30 min. Optical and structural properties of nanocomposite thin film with respect to high temperature are studied by UV-visible spectroscopy and x-ray diffraction, respectively. Transmission electron microscopy is performed to observe the temperature-dependent size evolution of Ag nanoparticles in fullerene C₇₀ matrix. A large growth of Ag nanoparticles is observed with temperature especially above 200 °C due to enhanced diffusion of Ag in fullerene C₇₀ at higher temperature and Ostwald ripening. The properties of metal-fullerene nanocomposite is not significantly affected up to a temperature of 150 °C. With a further increase in temperature, a major blue shift of ~?33 nm in SPR wavelength is seen at a temperature of 300 °C due to the thermal induced structural transformation of fullerene C₇₀ matrix into amorphous carbon. A very large-sized Ag nanoparticle with a wide size distribution varying from 27.8 ± 0.6 to 330.0 ± 4.5 nm is seen at 350 °C and due to which, a red shift of ~?16 nm is obtained at this temperature. This study throws light on the thermal stability of the devices based on metal-fullerene bi-functional nanocomposite.     

Oxygen doped SiC nanocrystals: first principles study of the optical properties

We have studied a typical spherical SiC nanocrystal with a diameter of 1.2 nm (Si₄₃C₄₄H₇₆) using linear combination of atomic orbitals in combination with pesudopotential density functional calculation. The role of fluorine and oxygen impurities was investigated on the electronic and optical properties of the Si₄₃C₄₄H₇₆ nanocrystal. Total energy calculations show that the fluorine doped Si₄₃C₄₄H₇₆ nanocrystals are unstable. Oxygen doped Si₄₃C₄₄H₇₆ have different binding energies in various substitutional and interstitial defects. The maximum binding energy of the oxygen at carbon substitutional defect is about ?0.5 eV and at interstitial defect is ?0.18 eV. The HOMO-LUMO gap of the pure Si₄₃C₄₄H₇₆ is about 6.71 eV and after doping with oxygen changes on the order of 0.1 eV. Our studies show that the refractive index of the doped Si₄₃C₄₄H₇₆ nanocrystal significantly dispersed in comparison with pure SiC nanocrystal especially at the range of 6 to 8 eV.