Individual and combined cytotoxicity effects of positively charged polystyrene nanoplastics and ionic surfactants on budding yeast Saccharomyces cerevisiae

It is of crucial importance to understand the impact of micro/nanoplastics contaminated with the other pollutants on microorganisms in the environment. In the present paper, we have investigated the individual and combined cytotoxicity effects of positively charged fluorescence-labeled polystyrene nanoparticles (pPS-NPs; 115 and 204 nm in diameter) and ionic surfactants [sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium chloride (C₁₂TAC)] on budding yeast Saccharomyces cerevisiae after a short-time exposure (0.5 h) in a 5-mM NaCl aqueous solution. In the absence of surfactants, the smaller 115-nm pPS-NPs were more cytotoxic than the larger 204-nm pPS-NPs. In the absence of pPS-NPs, the cationic surfactant of C₁₂TAC was more cytotoxic than the anionic surfactant of SDS, though these two ionic surfactants have the hydrophobic alkyl chains of the same length and the oppositely charged headgroups in the same magnitude. The addition of SDS decreased the number of pPS-NPs adhered on a negatively charged yeast cell to reduce the cytotoxicity, whereby the combined toxicity effect was considered as counteracting action. Although some addition of C₁₂TAC hardly influenced the number of pPS-NPs adhered on a yeast cell, the synergistic cytotoxicity action of the pPS-NPs and C₁₂TAC was observed.     

Adhesion and cytotoxicity of positively charged nanoparticles toward budding yeast Saccharomyces cerevisiae and fission yeast Schizosaccharomyces pombe

It is of great significance to examine the adverse effects of nanoparticles (NPs) on the environments and human health. In the present study, we have investigated the toxicological effects of NPs on two distinct strains of yeast, S. cerevisiae and S. pombe, in aqueous solutions of NaCl. The positively charged NPs of 100-nm diameter were more significantly adhered on (and uptaken by) a negatively charged cell of every yeast strain at lower ionic strength. Every yeast in 150-mM NaCl solution (high ionic strength) showed the cell viability of more than 80% even after exposure to 100-μg/mL NPs, whereas in 5-mM NaCl solution (low ionic strength) it exhibited zero cell viability at 25-μg/mL NPs. Interestingly, the dead cells in 5-mM NaCl solution containing 6.25–12.5 μg/mL NPs exhibited about 2-fold amount of cellular adhesion/uptake of NPs, compared with the corresponding live cells. The ratio between the saturated amounts of the cellular adhesion/uptake of NPs in 5-mM and 150-mM NaCl solutions for S. cerevisiae was about eighteen times greater than that for S. pombe. This behavior of S. cerevisiae is explained in part by the larger ratio between the zeta potentials of a cell in 5-mM and 150-mM NaCl solutions.     

Effect of salt concentration on adhesion and toxicity of positively charged polystyrene nanoplastics toward bacterium Escherichia coli compared with yeast Saccharomyces cerevisiae

It is of crucial importance to understand the impact of micro/nanoplastics on microorganisms in the environment. In the present paper, we have comprehensively investigated the effect of NaCl salt concentration (C_NaCl = 5–600 mM) on the adhesion and toxicity of positively charged polystyrene nanoparticles (pPS-NPs with 115-nm diameter) toward bacterium Escherichia coli K-12 after a short-time exposure (0.5 h) at 25 °C, in comparison with that toward yeast Saccharomyces cerevisiae. Unlike S. cerevisiae, the rod-shaped cells of E. coli exhibited the great surface potential in magnitude and the salt-concentration-dependent size with a minimum at C_NaCl = 100 mM. The adhesion and toxicity of pPS-NPs toward E. coli were similar to those toward S. cerevisiae, except for some points. Especially, the number of the NPs adhered to a cell as a function of C_NaCl at the higher NP mass doses exhibited an M-shaped profile with a local minimum at C_NaCl = 100 mM, which is mainly explained by the aforesaid salt-concentration-dependent cellular size. The E. coli cells significantly covered with pPS-NPs at C_NaCl = 100–150 mM remained alive. The tolerance of bacterium E. coli to exposure of NPs could result from its strong environmental adaptability.     

Control of colloidal behavior of polystyrene latex nanoparticles and their cytotoxicity toward yeast cells using water-soluble polymers

Positively charged polystyrene latex (PSL) nanoparticles (NPs) dispersed in physiological saline (154?mM NaCl solution) are taken up by yeast cells. However, in low ionic strength solutions, the yeast cells are covered with the NPs, leading to cell death. The environmental conditions under which NPs are taken up are therefore limited. In this study, we attempted to control the uptake of positively charged PSL NPs by Saccharomyces cerevisiae in 5?mM NaCl solution using a water-soluble polymer. Addition of a small amount of anionic sodium carboxymethylcellulose (CMC), which has a carboxyl group, to 5?mM NaCl solution allowed the uptake of PSL NPs by living yeast cells. In contrast, non-ionic methylcellulose did not affect the NP behavior. This is because the negatively charged CMC adhered to the positively charged PSL NP surfaces and the surface charge changed from positive to negative. Atomic force microscopy using a single-NP probe consisting of one NP immobilized on the flattened end of the silicon nitride tip showed that CMC significantly reduced the interaction force between a negatively charged living yeast cell and a positively charged PSL NP.     

In vitro cytotoxicity of monodispersed hematite nanoparticles on Hek 293 cells

A simple hydrothermal method was developed to prepare monodispersed and well-crystallized hematite nanoparticles with a diameter distribution of about 180 nm. In-vitro cytotoxicity of such nanoparticles was carried out using Hek 293 cell culture system with different dosages. Assessment of cell viability reveals that hematite nanoparticles reduce cell viability in a dose- and time-dependent manner within a rather wide dosage range. Such cytotoxicity is correlative to the decrease of the activity of antioxidative enzymes induced by the oxidative stress in cells.     

Effect of exposure temperature on the cell membrane disruption induced by amorphous silica nanoparticles in erythrocytes,lymphocytes, and malignant melanocytes

It is of great significance to examine carefully the potentially harmful effects of silica-based nanoparticles (NPs) on human body. In the present study, we have investigated the impact of exposure temperatures (4 °C, 15 °C, 26 °C, and 37 °C) on the cell membrane disruption induced by amorphous silica NPs of different primary diameters (28, 55, 88, 156, and 461 nm) in three different types of cells (erythrocytes, Jurkat, and B16F10), where the serum-free culture media were employed for exposure of the cells to the silica NPs. The size- and dose-dependent membranolytic activity of the silica NPs in each cell type at every temperature appeared to be given by a master curve as a function of the NP surface area per suspension volume, regardless of the NP diameter. This silica-induced membranolysis was significantly enhanced by the higher-temperature exposure of each cell type to the silica NPs. Such effects of exposure temperature on the silica-induced membranolysis in non-adherent cells of RBC and Jurkat were quite similar to each other, regardless of their difference in the presence/absence of nucleus and endocytic ability, whereas that for adherent cells of B16F10 was more remarkable. The filterability of erythrocytes also was measured at different temperatures, whereby the effect of temperature on the deformability of cell membranes was estimated. A possible mechanism underlying the effect of exposure temperature on the silica-induced membranolysis was proposed.     

Effect of residual stresses on mechanical properties and interface adhesion strength of SiN thin films

Residual stresses play a significant role in the mechanical reliability of thin films. Thus in this study, the mechanical properties and interface adhesion strengths of SiN thin films containing different residual stresses have been investigated by using nanoindentation and nanoscratch tests. With varied residual stresses from compressive to tensile, the penetration depth of nanoindentation tests shifted to a higher value. The hardness and elastic modulus decreased from 11.0 and 95 GPa, respectively, for the film containing a compressive stress of 235 MPa to 9.6 and 84 GPa for the film with a tensile stress of 86 MPa. With decreasing compressive stress and increasing tensile stress, the interface adhesion energy decreased from 1.8 to 1.5 J/m². Compressive stresses were expected to blunt crack tips and inhibit crack propagation, while tensile stresses enlarged crack opening and facilitated crack propagation, thus changing the mechanical properties of the SiN thin films.     

等离子体清洗工艺对镁基金属表面形貌及膜／基结合强度的影响

采用不同等离子体清洗工艺对镁基金属样品进行清洗,随后磁控溅射沉积纯Cr镀层.利用SEM、划痕仪分析了不同等离子体清洗工艺下镁基金属的表面形貌与膜／基结合强度的变化.结果表明,过高的清洗偏压作用下,基体表面会产生深径比＞0.5的孔洞状结构缺陷;过长清洗时间后,离子轰击产生的能量积淀效应使基体表面温升显著,局部区域出现熔融...     

Effect of Mn doping concentration on structural,vibrational and magnetic properties of NiO nanoparticles

The Ni_1?xMn_xO (x?=?0.00, 0.02, 0.04 and 0.06) nanoparticles were synthesized by chemical precipitation route followed by calcination at 500?°C for 4?h. The prepared samples were characterized by energy dispersive analysis of X-rays (EDAX), powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and vibrating sample magnetometer (VSM). Rietveld refinement of XRD data confirms the structural phase purity and XRD patterns are well indexed to NaCl like rock salt fcc crystal structure with Fm-3m space group. The particle size of Mn doped samples is found to be less than that of pure NiO sample. However, the particle size increases slightly on increasing the Mn concentration due to surface/grain boundary diffusion. The vibrational properties of the synthesized nanoparticles were investigated by Raman and FT-IR spectroscopy. The results of room temperature magnetization (M-H) and temperature dependent magnetization (M-T) measurements are explained with a core-shell model. The synthesized nanoparticles show weak ferromagnetic and super-paramagnetic like behavior at room temperature.     

本底真空度对磁控溅射Cr/C镀层微观形貌及结合强度的影响

采用闭合场非平衡磁控溅射离子镀技术于不同本底真空度下制备了Cr/C镀层。利用TEM、划痕仪分析了不同真空度下镀层微观截面形貌与结合强度的变化。结果表明,随本底真空度的降低,Cr/C镀层中物理混合界面层和Cr金属打底层的厚度显著减小;镀层结合强度随本底真空度的降低显著下降,物理混合界面层、Cr金属打底层厚度的减小以及镀层表面孔洞等缺陷增多、致密度变差等共同导致了其结合强度的下降。     

Effect of annealing temperature and pH on morphology and optical property of highly dispersible ZnO nanoparticles

Highly dispersible zinc oxide nanoparticles were produced in large quantity via a simple solution method. The effect of temperature and pH impact on as-prepared ZnO nanoparticles with respect to the morphological and optical characteristics has been investigated. The average particle size of ZnO nanoparticles increased with increasing annealing temperature. A sharp UV band-edge emission was observed in as-prepared ZnO nanoparticles with negligibly less intense deep level emission. However, upon annealing at high temperature in air, UV band-edge emission disappears with an evolution of a broad deep level emission in photoluminescence spectra. Similarly, by adjusting the pH of reaction medium from 4 to pH = 8 using ammonium hydroxide solution, particle size gets bigger and bigger leads to red-shift in UV band-edge emission and an appearance of deep level emission peak. At pH = 8, well resolved sharp X-ray diffraction peaks were observed with lower FWHM values due to higher crystallite sizes.     

Effect of salt concentration on the electrical and morphological properties of calcium phosphates obtained via microwave-induced combustion synthesis

Calcium phosphates (CaP) have been widely used in biomedical applications. One of the most versatile techniques for obtaining CaP is auto-combustion synthesis. This technique stands out because of its low cost and high efficiency; however, the difficulty of controlling the size and morphology of the product is its principal disadvantage. The aim of this study was to synthesize calcium phosphates through microwave-induced and salt-assisted solution combustion synthesis. The initial ratio of Ca/P was 1.5, employing urea as fuel and potassium chloride as an additive. The morphology and the electrical properties of CaP in relation to the amount of salt added were evaluated using scanning electron microscopy (SEM) and impedance spectroscopy, respectively. It was found that the inclusion of salt during the synthesis affects the morphology of calcium phosphates, creating whisker-like structures, with lengths approximately between 500 nm and 1 µm and widths between 30 nm and 300 nm, which depend on the salt concentration. Calcium pyrophosphate was the major phase of the synthetized product without the addition of salt, and hydroxyapatite (HAP) and chlorapatite (CAP) when salt was included. The dielectric constant exhibited lower values for the samples rich in calcium pyrophosphate and values between 16 and 32 for HAP and CAP at 1 kHz.     

Effect of long-term stress and temperature exposure on the fracture toughness of Ti-62222 alloy

Fracture toughness tests were conducted on a Ti-62222 (titanium alloy) sheet being considered for use in high temperature aircraft applications in the as received condition and after exposing the pre-cracked specimens to a sustained stress intensity, K, level between 55 and 60.5 MPa for 200 h at 350°C. It was concluded that the fracture toughness does not degrade as a result of exposure to high temperature and the K levels in this material. The tensile strength in the exposed condition also remained the same as in the as received condition.     

Effect of moisture content,temperature and exposure time on the physical stability of chitosan powder and tablets

Context: Chitosan does not rank highly regarding its employment as tablet filler due to certain limitations. Undesirable properties that limit its utilization as excipient in solid dosage forms include its hydration propensity that negatively affects tablet stability, strength and disintegration.

Objective: The objective of this study was to investigate the physical stability of chitosan powder, mixtures, granules and tablets under accelerated conditions such as elevated temperatures and humidity over different periods of time.

Methods: Selected physico-chemical properties of pure chitosan powder, physical mixtures of chitosan with Kollidon® VA64 (BASF, Ludwigshafen, Germany), chitosan granules, as well as tablets were evaluated under conditions of elevated humidity and temperature.

Results and discussion: The physical stability of chitosan tablets exhibited sensitivity towards varying exposure conditions. It was furthermore evident that the presence of moisture (sorbed water) had a marked influence on the physical stability of chitosan powder and tablets. It was evident that the presence of Kollidon® VA64 as well as the method of inclusion of this binder influenced the properties of chitosan tablets. The physical stability of chitosan powder deteriorated to a greater extent compared to that of the chitosan tablets, which were subjected to the same conditions.

Conclusion: It is recommended that tablets containing chitosan should be stored at a temperature not exceeding 25?°C as well as at a relatively low humidity (<60%) to prevent deterioration of physical properties. Direct compression of chitosan granules which contained 5%w/w Kollidon® VA64 produced the best formulation in terms of physical stability at the different conditions.     

Effect of anodic oxidation of coal tar pitch-based carbon fibre on adhesion in epoxy matrix: Part 1. Comparison between H2SO4 and NaOH solutions

Anodic oxidation of high modulus coal tar pitch-based carbon fibre in alkaline and sulfuric solutions was investigated. X-ray photoelectron spectroscopy (XPS) analysis was used to evaluate the oxygen concentration (O_1S/C_1S) and surface functional groups (---OH, C=O and COOH). The interfacial shear strength between the epoxy matrix and carbon fibre was measured by a fragmentation test. The results showed that the oxygen concentration on fibre surfaces increased rapidly as electrical charge increased, in both alkaline and acidic solution. The best bonding between epoxy matrix and carbon fibre was achieved in alkaline solution. The Raman spectra of carbon fibre oxidized in alkaline and sulfuric solutions suggested that the weak adhesive strength between the epoxy resin and oxidized carbon fibre in sulfuric solution was due to the existence of an oxidized graphite layer, which might easily come off the surface.     

Effect of different concentration Li-doping on the morphology,defect and photovoltaic performance of Li–ZnO nanofibers in the dye-sensitized solar cells

Low concentrations of Li in Li-doped ZnO nanofibers prepared using hydrothermal method at low temperature can introduce oxygen vacancies and intrinsic Zn ions into the structure. Photo-luminance (PL) was used to investigate oxygen vacancies in the structure of ZnO nanofibers prepared by lower annealing temperature, and the XPS technique was also employed to satisfy the PL analysis results. PL analysis showed that oxygen vacancies increase in conjunction with Li concentrations. A shift in the lower angle of XRD patterns also demonstrates the defect in ZnO structure related to Li doping. Higher-efficiency DSSCs were obtained from the lower Li concentration of 0.01 M in ZnO nanofibers. Higher concentrations of Li tended to produce large amounts of cross-like nanofibers, which increase the open circuit voltage of the DSSCs. The highest open circuit voltage (V_oc) obtained was 750 mV, which was higher than the best reported ZnO nanofibers-based DSSCs. Intensity modulation photocurrent spectroscopy (IMPS) and intensity modulation photo-voltage spectroscopy (IMVS) analysis showed that low amounts of Li-doping improved the electron injection efficiency of ZnO nanofibers in DSSCs. Lower recombination rates with higher electron transfer efficiency for 0.01 M Li-doped DSSCs exhibited higher efficiency of 0.59% than non-doped ZnO nanofibers DSSCs.