M. Milosavljević

Large graphene quantum dots alleviate immune-mediated liver damage.

We investigated the effect of large (40 nm) graphene quantum dots (GQDs) in concanavalin A (Con A; 12 mg/kg i.v.)-induced mouse hepatitis, a T cell-mediated liver injury resembling fulminant hepatitis in humans. Intravenously injected GQDs (50 mg/kg) accumulated in liver and reduced Con A-mediated liver damage, as demonstrated by histopathological analysis and a decrease in liver lipid peroxidation and serum levels of liver transaminases. The cleavage of apoptotic markers caspase-3/PARP and mRNA levels of proapoptotic mediators Puma, Noxa, Bax, Bak1, Bim, Apaf1, and p21, as well as LC3-I conversion to autophagosome-associated LC3-II and expression of autophagy-related (Atg) genes Atg4b, Atg7, Atg12, and beclin-1, were attenuated by GQDs, indicating a decrease in both apoptosis and autophagy in the liver tissue. This was associated with the reduced liver infiltration of immune cells, particularly the T cells producing proinflammatory cytokine IFN-γ, and a decrease in IFN-γ serum levels. In the spleen of GQD-exposed mice, mRNA expression of IFN-γ and its transcription factor T-bet was reduced, while that of the IL-33 ligand ST2 was increased. The hepatoprotective effect of GQDs was less pronounced in ST2-deficient mice, indicating that it might depend on ST2 upregulation. In vitro, GQDs inhibited splenocyte IFN-γ production, reduced the activation of extracellular signal-regulated kinase in macrophage and T cell lines, inhibited macrophage production of the free radical nitric oxide, and reduced its cytotoxicity toward hepatocyte cell line HepG2. Therefore, GQDs alleviate immune-mediated fulminant hepatitis by interfering with T cell and macrophage activation and possibly by exerting a direct hepatoprotective effect.

Raman spectroscopy study of carbon-doped resorcinol-formaldehyde thin films

In this work, we investigated the properties of carbon resorcinol-formaldehyde (RF) cryogel thin films. RF cryogels were doped by single-wall carbon nanotubes, graphene and graphene quantum dots. The structure of the deposited films was investigated by Raman spectroscopy, and optical, transmission electron and atomic force microscopy. Raman spectroscopy was performed using three excitation laser energies in the visible range. The effect of glass substrate on the Raman features of investigated carbon cryogel thin films was determined as well. The particle size of the carbon-doped RF cryogel thin films was determined by atomic force microscopy.

Selective Al-Ti reactivity in laser-processed Al/Ti multilayers

ABSTRACT Multilayers consisting of five (Al/Ti) bilayers were deposited on (100) silicon wafers. On top was deposited the Ti layer, aimed at preventing Al from diffusing to the surface upon laser treatment. The total thickness of the thin-film structure was 200 nm. Laser irradiations with Nd:YAG picoseconds laser pulses in the defocused regime were performed in air. Laser beam energy was 4 mJ and laser spot diameter on the sample surface was 3 mm (fluence 0.057 J cm−2). The samples were treated with different numbers of laser pulses. Structural characterizations were performed by different analytical methods and nano-hardness was also measured. Laser processing induced layer intermixing, formation of titanium aluminides, oxidation of the surface titanium layer and enhanced surface roughness. Aluminum appears at the sample surface only for the highest density of laser irradiation. Laser processing induces increment of nano-hardness by approximately 20% and decrease of residual Young’s modulus for a few percentages from the starting value of the untreated samples. These results can be interesting toward achieving structures with a selective extent of Al-Ti reactivity in this multilayered system, within the development of biocompatible materials.

Intermixing in Al/Ti multilayer structures induced by nanosecond laser pulses

Structural and compositional modifications of multilayered Al/Ti nano-structures induced by nanosecond laser pulses were investigated. Five and ten (Al/Ti) bilayers, with total thicknesses of 130 and 260 nm, respectively, were deposited by dc ion sputtering onto (100) Si wafers. The structures were irradiated in air with nanosecond Nd:YAG unfocused laser pulses. Characterizations of the samples were performed by x-ray diffraction analysis, Auger electron spectroscopy, atomic force microscopy and transmission electron microscopy. It was found that laser treatment of both structures induced complete intermixing of all deposited metallic films, their mixing with silicon substrate and formation of Al–Ti intermetallic and silicide compounds. This effect was achieved even for one applied laser pulse. Comparing these results with that for picosecond laser treatment of similar multilayered structures, it was concluded that materials involved within the heat diffusion length participated in the formation of new phases.

Evaluation of the composition and morphology of a WTi/Si system processed by a picosecond laser

In this work we studied the influence of laser radiation on the composition, structure and morphology of WTi thin films deposited on n-type (100) silicon wafers. The films were deposited by d.c. sputtering from a 70:30 at% W-Ti target, using Ar ions, to a thickness of ∼190 nm. Irradiation was performed with a pulsed Nd:YAG laser operating at 1064 nm, whereas the pulse duration was 150 ps. Laser fluences of 3.2 and 5.9 J/cm2 were found to be sufficient for modification of the WTi/silicon target system. The results show: (i) ablation of WTi thin film and a Si substrate in the central zone of spots, (ii) appearance of hydrodynamic features like resolidified material, (iii) partial ablation of the WTi thin film at the periphery and (iv) appearance of thin film cracks at the far periphery. On the non-ablated areas, the laser modification induced changes in composition, such as inter-mixing of components at the WTi/Si interface with formation of silicides in both metals. Surface oxidation was the dominant process in the ablated areas, which is demonstrated by the presence of a SiO2 phase.