Publications

In this study, we report the implications of the synthesis method on Gd2O3 sensitivity to CO2. The rare-earth oxide was prepared by wet chemical co-precipitation and by hydrothermal method. The obtained powders labelled Gd2O3-CoP and Gd2O3-HT were deposited as thick films over commercial Al2O3 substrates provided with Pt electrodes and a back-side heater. Both powders consist of the same crystallographic phase, with a significant difference appearing in selected area electron diffraction patterns, transmission electron microscopy images at higher magnification and X-ray diffraction spectra, with respect to the crystallization degree. The associated role in sensing properties is revealed via electrical resistance variations determined by CO2 concen-trations in the range between 400 and 3000 ppm and variable relative humidity between 0 and 50%RH, similar to the in-field atmosphere. The proposed CO2 interaction mechanism is based on phenomenological in-vestigations which highlight the electronic affinity variation as the effect of dipoles induced by the in-field conditions on the Gd2O3 surface.

Hybrid layers consisting of Fe oxide, Fe hydroxide, and nitrogen doped graphene-like platelets have been synthesized by an eco-friendly laser-based method for photocatalytic applications. The complex composite layers show high photodecomposition efficiency towards degradation of antibiotic molecules under visible light irradiation. The photodecomposition efficiency was investigated as a function of relative concentrations of base materials, Fe oxide nanoparticles and graphene oxide platelets used for the preparation of target dispersions submitted to laser irradiation. Although reference pure Fe oxide/Fe hydroxide layers have high absorption in the visible spectral region, their photodecomposition efficiency is negligible under the same irradiation conditions. The high photocatalytic decomposition efficiency of the nanohybrid layer, up to 80% of the initial antibiotic molecules was assigned to synergistic effects between the constituent materials, efficient separation of the electron-hole pairs generated by visible light irradiation on the surface of Fe oxide and Fe hydroxide nanoparticles, in the presence of conducting graphene-like platelets. Nitrogen doped graphene-like platelets contribute also to the generation of electron-hole pairs under visible light irradiation, as demonstrated by the photocatalytic activity of pure, reference nitrogen doped graphene-like layers. The results also showed that adsorption processes do not contribute significantly to the removal of antibiotic molecules from the test solutions. The decrease of the antibiotic concentration under visible light irradiation was assigned primarily to photocatalytic decomposition mechanisms.

Hydrogen production from methanol decomposition to syngas (H2 + CO) is a promising alternative route for clean energy transition. One major challenge is related to the quest for stable, cost-effective, and selective catalysts operating below 400 degrees C. We illustrate an investigation of the surface reactivity of a Ni3Sn4 catalyst working at 250 degrees C, by combining density functional theory, operando X-ray absorption spectroscopy, and high-resolution transmission electron microscopy. We discovered that the catalytic reaction is driven by surface tin-oxide phases, which protects the underlying Ni atoms from irreversible chemical modifications, increasing the catalyst durability. Moreover, we found that Sn content plays a key role in enhancing the H2 selectivity, with respect to secondary products such as CO2. These findings open new perspectives for the engineering of scalable and low-cost catalysts for hydrogen production.

Lanthanide (Ln) co-doped transition metal (TM) upconversion (UC) co-doped systems are being intensively investigated for their exciting applications in photonics, bioimaging, and luminescence thermometry. The presence of TM, such as Mo6 + /W6 +, Mn2 +, or Fe3 + determines significant changes in Ln UC emission, such as intensity enhancement, colour modulation, and even the alteration of the photon order. The current mechanism assumes a ground-state absorption/excited-state absorption (ESA/GSA) in TM-Yb dimer followed by direct energy transfer to Er/Tm excited states. We revisit this mechanism by addressing two issues that remain ignored: a dynamical approach to the investigation of the upconversion mechanism and the intrinsic chemical complexity of co-doped TM, Ln systems. To this aim, we employ a pulsed, excitation variable laser across a complete set of UC measurements, such as the emission and excitation spectra and emission decays and analyze multiple grains with transmission electron microscopy (TEM). In the Mo co-doped garnet, the results sustain the co-existence of Mo-free garnet and Mo oxide impurity. In this Mo oxide, the Er upconversion emission properties are fully explained by a relatively efficient sequential Yb to Er upconversion process, with no contribution from Yb-Mo dimer sensitization.

In the present work, nanocrystalline NixCo1-xFe2O4 oxides with average crystallite size between 11 nm and 111 nm have been analyzed by Mossbauer spectroscopy, hysteresis loops, field cooled (FC) and zero field cooled (ZFC) magnetization measurements. A core-shell model has been proposed. Accordingly, the Mossbauer spectra evidence a ferrimagnetic core and a disordered shell (spin-glass), the latter increasing with Ni concentration. Hysteresis curves reveal the ferromagnetic nature of the investigated compounds and transformation from single- to multi-domain behaviour at a critical particle size dependent on Ni2+ ion concentration. The magnetic properties of finest powders (average crystallite size similar to 11 nm) are the most sensitive to the Ni2+ ions content. A general increase in the coercive field, H-C, with reducing temperature according to the modified Kneller's formula H-c(T) = H-c(0)[1-(T/T-B)(beta) where beta = 0.45 occurs. A high saturation magnetization of about 90 emu/g and an increase in H-C from about 0.3 kOe at 300 K to 7 kOe at 10 K have been observed for the sample Ni0.1Co0.9Fe2O4 (x = 0.1). Increasing magnetization and coercive field with reducing temperature are also explained within the core shell model. FC and ZFC data show strong dependence of the magnetic properties on crystallite size and concentration of Ni2+ ions.

A sensor for the enzymatic activity and inhibition of the 20S proteasome was developed by immobilizing the synthetic peptide ABZ-VVSYAMG-(O2Oc)2-OH at Au electrodes. The detection principle is based on the elec-troactivity of ABZ, part of the ABZ-VVSY-OH moiety released from the peptide upon 20S proteasome chymo-trypsin action. The peptide was immobilized on a para-amino thiophenol (PATP) self-assembled monolayer on Au electrode by cross-linking its amino group to the -(O2Oc)2-OH moiety of the peptide (Au/PATP/peptide). The immobilization of the peptide and its interaction with 20S proteasome was investigated by SEM, QCM, SPR, ATR-FTIR and electrochemistry. The activity of 20S proteasome was assessed electrochemically by cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) after the immersion Au/PATP/peptide in 20S proteasome solution. CV study showed a decrease in both capacitive and faradaic currents corresponding to the ABZ-VVSY-OH removal, allowing the quantification of the 20S proteasome activity. The EIS study revealed that the resis-tance corresponding to charge transfer reactions at the peptide/solution interface correlated to the ABZ redox reaction, decreased linearly with increasing the incubation time in 20S proteasome solution. The perfected assay was applied for the investigation of the inhibitory effect of one synthetic, bortezomib, and two naturally occurring, epoxomicin, and lactacystin inhibitors.

Yttrium iron garnet nanoparticles were exposed to mechanochemical activation by high-energy ball milling for 0, 2, 4, 8 and 12 h, with and without graphene nanoparticles. The samples were subsequently characterized by Mo center dot ssbauer spectroscopy, X-ray powder diffraction (XRPD), magnetic measurements and optical diffuse reflec-tance spectroscopy. Examination of the quadrupole doublet's abundance as function of ball milling time indi-cated that graphene slowed down the precipitation of the yttrium iron perovskite (yttrium orthoferrite) phase. The increased linewidth of the doublet showed that the carbon from graphene preferentially entered the lattice of the yttrium orthoferrite. The saturation magnetization decreased with decreasing particle size for prolonged milling due to the occurrence of the antiferromagnetic hematite phase. The enhanced absorption in the infrared region could be associated with the incorporation of carbon from graphene in the lattice of the yttrium ortho-ferrite. The results are interesting for sensing and microwave applications.

The changes of properties and preferential interactions based on subtle energetic differences are important characteristics of organic molecules, particularly for their functionalities in biological systems. Only slightly energetically favored interactions are important for the molecular adsorption and bonding to surfaces, which define their properties for further technological applications. Here, prochiral tetracenothiophene molecules are adsorbed on the Cu(111) surface. The chiral adsorption configurations are determined by Scanning Tunneling Microscopy studies and confirmed by first-principles calculations. Remarkably, the selection of the adsorption sites by chemically different moieties of the molecules is dictated by the arrangement of the atoms in the first and second surface layers. Furthermore, we have investigated the thermal effects on the direct desulfurization reaction that occurs under the catalytic activity of the Cu substrate. This reaction leads to a product that is covalently bound to the surface in chiral configurations.

Iron oxide nanoparticles are one of the most promising tools for theranostic applications of pancreatic cancer due to their unique physicochemical and magnetic properties making them suitable for both diagnosis and therapy. Thus, our study aimed to characterize the properties of dextran-coated iron oxide nanoparticles (DIO-NPs) of maghemite (gamma-Fe2O3) type synthesized by co-precipitation and to investigate their effects (low-dose versus high-dose) on pancreatic cancer cells focusing on NP cellular uptake, MR contrast, and toxicological profile. This paper also addressed the modulation of heat shock proteins (HSPs) and p53 protein expression as well as the potential of DIO-NPs for theranostic purposes. DIO-NPs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic light scattering analyses (DLS), and zeta potential. Pancreatic cancer cells (PANC-1 cell line) were exposed to different doses of dextran-coated gamma-Fe2O3 NPs (14, 28, 42, 56 mu g/mL) for up to 72 h. The results revealed that DIO-NPs with a hydrodynamic diameter of 16.3 nm produce a significant negative contrast using a 7 T MRI scanner correlated with dose-dependent cellular iron uptake and toxicity levels. We showed that DIO-NPs are biocompatible up to a concentration of 28 mu g/mL (low-dose), while exposure to a concentration of 56 mu g/mL (high-dose) caused a reduction in PANC-1 cell viability to 50% after 72 h by inducing reactive oxygen species (ROS) production, reduced glutathione (GSH) depletion, lipid peroxidation, enhancement of caspase-1 activity, and LDH release. An alteration in Hsp70 and Hsp90 protein expression was also observed. At low doses, these findings provide evidence that DIO-NPs could act as safe platforms in drug delivery, as well as antitumoral and imaging agents for theranostic uses in pancreatic cancer.

Presently, iron oxide nanoparticles are the only ones approved for clinical use as contrast agents in magnetic resonance imaging (MRI). Even though there is a high demand for these types of nanoparticles both for clinical use as well as for research, there are difficulties in obtaining stable nanoparticles with reproducible properties. In this context, in this study, we report the obtaining by an adapted coprecipitation method of dextran-coated maghemite nanoparticles (gamma-Fe2O3 NPs). The morphology and structure of the dextran-coated maghemite nanoparticles (gamma-Fe2O3 NPs) were determined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The TEM and SEM micrographs highlighted the obtaining of particles of nanometric size and spherical shape morphology. Furthermore, the high-resolution transmission electron microscopy (HRTEM), as well as selected area diffraction (SAED), revealed that the obtained samples presented the structure of cubic maghemite. In this study, we also explored the effects of the co-precipitation synthesized dextran-coated maghemite nanoparticles (gamma-Fe2O3 NPs) on the redox status of macrophages. For cytotoxicity evaluation of these NPs, murine macrophages (RAW 264.7 cell line) were exposed to different concentrations of dextran-coated maghemite nanoparticles (gamma-Fe2O3 NPs) corresponding to 0-500 mu g Fe3+/mL and incubated for 24, 48, and 72 h. Intracellular iron uptake, changes in the oxidative stress parameters (reactive oxygen species production and malondialdehyde level), and the activity of antioxidant enzymes, as well as GSH concentration in cells, were evaluated after incubation with a lower (50 mu g Fe3+/mL) and higher (500 mu g Fe3+/mL) dose of NPs. The results indicated a significant decrease in RAW 264.7 cell viability after 72 h in the presence of NPs at concentrations above 25 mu g Fe3+/mL. An important accumulation of NPs, dependent on dose and exposure time, was detected in macrophages, but it induced only a limited raise in the oxidative status. We showed here that the antioxidant capacity of RAW 264.7 macrophages was efficient in counteracting dextran-coated maghemite nanoparticles (gamma-Fe2O3 NPs) toxicity even at higher doses.