One-step sputtering of MoSSe metastable phase as thin film and predicted thermodynamic stability by computational methods

We present the fabrication of a MoS2-xSex thin film from a co-sputtering process using MoS2 and MoSe2 commercial targets with 99.9% purity. The sputtering of the MoS2 and MoSe2 was carried out using a straight and low-cost magnetron radio frequency sputtering recipe to achieve a MoS2-xSex phase with x = 1 and sharp interface formation as confirmed by Raman spectroscopy, time-of-flight secondary ion mass spectroscopy, and cross-sectional scanning electron microscopy. The sulfur and selenium atoms prefer to distribute randomly at the octahedral geometry of molybdenum inside the MoS2-xSex thin film, indicated by a blue shift in the A1g and E1g vibrational modes at 355 cm-1 and 255 cm-1, respectively. This work is complemented by computing the thermodynamic stability of a MoS2-xSex phase whereby density functional theory up to a maximum selenium concentration of 33.33 at.% in both a Janus-like and random distribution. Although the Janus-like and the random structures are in the same metastable state, the Janus-like structure is hindered by an energy barrier below selenium concentrations of 8 at.%. This research highlights the potential of transition metal dichalcogenides in mixed phases and the need for further exploration employing low-energy, large-scale methods to improve the materials' fabrication and target latent applications of such structures.

Longitudinal chemokine profile expression in a blood-brain barrier model from Alzheimer transgenic versus wild-type mice

BACKGROUND

Alzheimer's disease is widely described since the discovery of histopathological lesions in Mrs. Auguste Deter in 1906. However to date, there is no effective treatment to deal with the many cellular and molecular alterations. The complexity is even higher with the growing evidence of involvement of the peripheral blood mononuclear cells (PBMCs). Indeed, monocytes and T cells are shown in the cerebral parenchyma of AD patients, and these cells grafted to the periphery are able to go through the blood-brain barrier (BBB) in transgenic mouse models. It is known that BBB is disrupted at a late stage of AD. Chemokines represent major regulators of the transmigration of PBMCs, but many data were obtained on AD animal models. No data are available on the role of AD BBB in a healthy brain parenchyma. Therefore, the purpose of this study was to analyze the longitudinal chemokine profile expression in a BBB model from AD transgenic mice versus wild-type (WT) mice.

METHODS

A primary mouse BBB model was used with a luminal compartment either AD or WT and an abluminal compartment WT consisting of astrocytes and microglia. PBMCs were extracted by a ficoll gradient and incubated in the transwell with a direct contact with the luminal side, including the endothelial cells and pericytes. Then, the complete BBB model was incubated during 48 h, before supernatants and cell lysates were collected. Chemokines were quantified by X-MAP® luminex technology.

RESULTS

Abluminal CX3CL1 production increased in 12-month-old AD BBB while CX3CL1 levels decreased in luminal lysates. CCL3 in luminal compartment increased with aging and was significantly different compared to AD BBB at 12 months. In addition, abluminal CCL2 in 12-month-old AD BBB greatly decreased compared to levels in WT BBB. On the contrary, no modification was observed for CCL4, CCL5, and CXCL10.

CONCLUSION

These first findings highlighted the impact of AD luminal compartment on chemokine signature in a healthy brain parenchyma, suggesting new therapeutic or diagnostic approaches.

Comparative evaluation of biofilm formation and tolerance to a chemical shock of pathogenic and nonpathogenic Escherichia coli O157:H7 strains

Seven Escherichia coli O157:H7 strains, three pathogenic (including epidemic EDL933 and Sakai) and four nonpathogenic (including mutants of EDL933 and Sakai), were compared to find a model strain to avoid the use of European third-class biological agents in biofilm studies. Comparison was performed on attached populations reached at the end of growth in eight environmental conditions defined as the combinations of three two-level factors: (i) culture medium composed of meat exudate and glucose-supplemented minimal salts medium (MSM), (ii) growth temperatures of 15 and 25 degrees C, and (iii) materials of stainless steel and polyurethane. The influence of each of these four factors (strain, medium, temperature, and material) often depended on the level of at least one of the others. Exudate produced attached populations that were larger than or similar to those obtained with MSM, except for EDL933 mutant at 15 degrees C. When exudate led to larger populations than did MSM, the highest differences of up to 1.8 log CFU/cm2 were observed with the nonepidemic strains grown at 25 degrees C. Populations of these strains were not significantly different in any of the conditions studied, but they were different from the epidemic strains in some conditions. No nonpathogenic mutant was representative of its parental strain. Furthermore, the Sakai mutant biofilm was significantly more reduced than its parental strain was after chemical shock. It is therefore not possible to find a surrogate of either EDL933 or Sakai, and it is advisable that main results be validated on a pathogenic strain whenever nonpathogenic strains are used.

Behaviour of L. monocytogenes in an artificially made biofilm of a nisin-producing strain of Lactococcus lactis

The survival of Listeria monocytogenes in a binary biofilm with a bacteriocin producer (Lactococcus lactis CNRZ 150) was investigated. Two situations were simulated: in the first, L. monocytogenes was deposited on a 1-day biofilm of Lactococcus lactis (deferred adhesion); in the second, L. monocytogenes was simultaneously mixed with Lact. lactis (simultaneous adhesion). Biofilms were cultivated in tryptic soy broth supplemented with 6 g l(-1) of yeast extract (TSB-YE) and L. monocytogenes counts were followed for 48 h, both in co-culture with Lact. lactis and in pure culture. The influence of the mode of inoculation of L. monocytogenes (deferred or simultaneous adhesion) into the Lact. lactis biofilm, the size of the L. monocytogenes inoculum and the replacement of the culture medium at 20-24 h on the survival of L. monocytogenes was studied. Results showed that the antilisterial activity of the Lact. lactis started within the first 6 h of the deposition of L. monocytogenes. The log cycle reduction rate in number of L. monocytogenes in the mixed biofilm (compared to the pure biofilm) was greatly dependent on the inoculum size: when the smallest inoculum was used to colonise stainless steel coupons (10(6)-10(7) CFU ml(-1)), the log cycle reduction was greater and L. monocytogenes was not detected after t = 10 h (simultaneous adhesion) and t = 24 h (deferred adhesion) in the adherent population as well as in the planktonic population. On the other hand, in the case of a greater supply of L. monocytogenes (10(8) CFU ml(-1)), the results showed that the early reduction of L. monocytogenes counts was relatively slow and was followed by a stabilisation of the population, leading to the establishment of a great number of resident cells in the biofilm (10(5) to 106 CFU cm(-2)). This population level was maintained during the 48 h of experimentation and replacement of the culture media with fresh medium at t = 22 h (simultaneous adhesion) or t = 24 h (deferred adhesion) did not modify the level of the population of L. monocytogenes within the biofilm.