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1.
J Phys Chem B ; 124(24): 4931-4948, 2020 Jun 18.
Artigo em Inglês | MEDLINE | ID: mdl-32407114

RESUMO

Magnetite nanoparticles (MNPs) were synthesized using two distinctly different approaches, co-precipitation (CP) and thermal decomposition (TD), and further surface functionalized with organophosphonic ligands containing different numbers of phosphonic groups. We have shown that it is possible to fabricate flower-like assemblies of MNPs through TD at lower temperatures, whereas CP MNPs formed agglomerates of particles with broad size distribution and irregular shapes. The effect of the organophosphonic ligands on the heating efficiency of the TD and CP MNPs under dual mode stimulation (simultaneous action of AMF and NIR laser radiation) was studied for the first time. It was found that in the case of the cost-effective CP MNP synthesis surface functionalization with chosen phosphonic ligands leads to higher heating efficiency upon laser stimulation, whereas better performance of TD MNPs was found under the action of AMF due to the significant difference of nanoparticle properties. The biocompatibility of surface functionalized MNPs with organophosphonic ligands was evaluated through thorough studies of the metabolic activity of MNPs in normal human foreskin fibroblasts as well as oxidative stress induction and oxidation stress response which has not been previously reported for most of the organophosphonic moieties used in this study.

2.
Microb Cell Fact ; 18(1): 210, 2019 Dec 03.
Artigo em Inglês | MEDLINE | ID: mdl-31796078

RESUMO

BACKGROUND: Synthesis of nanoparticles (NPs) and their incorporation in materials are amongst the most studied topics in chemistry, physics and material science. Gold NPs have applications in medicine due to their antibacterial and anticancer activities, in biomedical imaging and diagnostic test. Despite chemical synthesis of NPs are well characterized and controlled, they rely on the utilization of harsh chemical conditions and organic solvent and generate toxic residues. Therefore, greener and more sustainable alternative methods for NPs synthesis have been developed recently. These methods use microorganisms, mainly yeast or yeast cell extract. NPs synthesis with culture supernatants are most of the time the preferred method since it facilitates the purification scheme for the recovery of the NPs. Extraction of NPs, formed within the cells or cell-wall, is laborious, time-consuming and are not cost effective. The bioactivities of NPs, namely antimicrobial and anticancer, are known to be related to NPs shape, size and size distribution. RESULTS: Herein, we reported on the green synthesis of gold nanoparticles (AuNPs) mediated by pyomelanin purified from the yeast Yarrowia lipolytica. A three levels four factorial Box-Behnken Design (BBD) was used to evaluate the influence of temperature, pH, gold salt and pyomelanin concentration on the nanoparticle size distribution. Based on the BBD, a quadratic model was established and was applied to predict the experimental parameters that yield to AuNPs with specific size. The synthesized nanoparticles with median size value of 104 nm were of nanocrystalline structure, mostly polygonal or spherical. They exhibited a high colloidal stability with zeta potential of - 28.96 mV and a moderate polydispersity index of 0.267. The absence of cytotoxicity of the AuNPs was investigated on two mammalian cell lines, namely mouse fibroblasts (NIH3T3) and human osteosarcoma cells (U2OS). Cell viability was only reduced at AuNPs concentration higher than 160 µg/mL. Moreover, they did not affect on the cell morphology. CONCLUSION: Our results indicate that different process parameters affect significantly nanoparticles size however with the mathematical model it is possible to define the size of AuNPs. Moreover, this melanin-based gold nanoparticles showed neither cytotoxicity effect nor altered cell morphology.


Assuntos
Ouro/metabolismo , Melaninas/metabolismo , Nanopartículas Metálicas/química , Yarrowia/metabolismo , Animais , Sobrevivência Celular/efeitos dos fármacos , Células Cultivadas , Coloides/química , Coloides/farmacologia , Ouro/química , Ouro/farmacologia , Humanos , Melaninas/biossíntese , Melaninas/isolamento & purificação , Camundongos , Células NIH 3T3 , Propriedades de Superfície , Yarrowia/citologia , Yarrowia/crescimento & desenvolvimento
3.
Micromachines (Basel) ; 10(9)2019 Aug 23.
Artigo em Inglês | MEDLINE | ID: mdl-31450725

RESUMO

This paper has three main purposes. The first is to investigate whether it is appropriate to use a planar thick-film thermoelectric sensor to monitor the temperature difference in a processor heat sink. The second is to compare the efficiency of two heat sink models. The third is to compare two kinds of sensors, differing in length. The model of the CPU heat sink sensor system was designed for numerical simulations. The relations between the CPU, heat sink, and the thermoelectric sensor were modelled because they are important for increasing the efficiency of fast processors without interfering with their internal structure. The heat sink was mounted on the top of the thermal model of a CPU (9.6 W). The plate fin and pin fin heat sinks were investigated. Two planar thermoelectric sensors were mounted parallel to the heat sink fins. These sensors monitored changes in the temperature difference between the CPU and the upper surface of the heat sink. The system was equipped with a cooling fan. Switching on the fan changed the thermal conditions (free or forced convection). The simulation results showed the temperature gradient appearing along the sensor for different heat sinks and under different thermal conditions. Comparison of the results obtained in the simulations of the CPU heat sink sensor systems proves that changes in the cooling conditions can cause a strong, step change in the response of the thermoelectric sensor. The results suggest that usage of the pin fin heat sink model is a better solution for free convection conditions. In the case of strong forced convection the heat sink type ceases to be significant.

4.
Food Chem ; 268: 567-576, 2018 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-30064798

RESUMO

Interaction of metal, especially iron ions with flavanols is considered as an important feature of these compounds and is believed to contribute to their both antioxidant and prooxidant properties. The aim of this study was to examine how Fe2+ binding to form a 4:1 (flavanol:Fe2+) mixtures affects the antioxidant properties of flavanols. ABTS∗ scavenging, protection against fluorescence bleaching induced by AAPH and hypochlorite, protection against lipid peroxidation and protection against hypochlorite-induced hemolysis demonstrated that flavonol-Fe2+ mixtures retain antioxidant properties, although, in most cases, they are lower with respect to the flavanols alone. No superoxide dismutase-like or catalase-like activity of the mixtures was revealed.


Assuntos
Antioxidantes/química , Polifenóis/química , Flavonóis , Peroxidação de Lipídeos
5.
Materials (Basel) ; 11(1)2018 Jan 12.
Artigo em Inglês | MEDLINE | ID: mdl-29329203

RESUMO

This paper describes the design, manufacturing and characterization of newly developed mixed thick-/thin film thermoelectric microgenerators based on magnetron sputtered constantan (copper-nickel alloy) and screen-printed silver layers. The thermoelectric microgenerator consists of sixteen thermocouples made on a 34.2 × 27.5 × 0.25 mm³ alumina substrate. One of thermocouple arms was made of magnetron-sputtered constantan (Cu-Ni alloy), the second was a Ag-based screen-printed film. The length of each thermocouple arm was equal to 27 mm, and their width 0.3 mm. The distance between the arms was equal to 0.3 mm. In the first step, a pattern mask with thermocouples was designed and fabricated. Then, a constantan layer was magnetron sputtered over the whole substrate, and a photolithography process was used to prepare the first thermocouple arms. The second arms were screen-printed onto the substrate using a low-temperature silver paste (Heraeus C8829A or ElectroScience Laboratories ESL 599-E). To avoid oxidation of constantan, they were fired in a belt furnace in a nitrogen atmosphere at 550/450 °C peak firing temperature. Thermoelectric and electrical measurements were performed using the self-made measuring system. Two pyrometers included into the system were used for temperature measurement of hot and cold junctions. The estimated Seebeck coefficient, α was from the range 35 - 41 µV/K, whereas the total internal resistances R were between 250 and 3200 ohms, depending on magnetron sputtering time and kind of silver ink (the resistance of a single thermocouple was between 15.5 and 200 ohms).

6.
ACS Appl Mater Interfaces ; 9(38): 33250-33256, 2017 Sep 27.
Artigo em Inglês | MEDLINE | ID: mdl-28885819

RESUMO

Magnetic nanostructures revealing exchange bias effect have gained a lot of interest in recent years due to their possible applications in modern devices with various functionalities. In this paper, we present our studies on patterned [CoO/Co/Pd]10 multilayer where ferromagnetic material is in a form of clusters, instead of being a continuous layer. The system was patterned using nanosphere lithography technique which resulted in creation of an assembly of well-ordered antidots or islands over a large substrate area. We found that the overall hysteresis loop of the films consists of hard and soft components. The hard component hysteresis loop exhibits a large exchange bias field up to -11 kOe. The patterning process causes a slight increase of the exchange field as the antidot radius rises. We also found that the material on edges of the structures gives rise to a soft unbiased magnetization component.

7.
ACS Appl Mater Interfaces ; 8(41): 28159-28165, 2016 Oct 19.
Artigo em Inglês | MEDLINE | ID: mdl-27648930

RESUMO

Magnetic systems exhibiting an exchange bias effect are being considered as materials for applications in data storage devices, sensors, and biomedicine. Because the size of new magnetic devices is being continuously reduced, the influence of thermally induced instabilities in magnetic order has to be taken into account during their fabrication process. In this study, we show the influence of superparamagnetism on the magnetic properties of an exchange-biased [CoO/Co/Pd]10 multilayer. We find that the process of progressive thermal blocking of the superparamagnetic clusters causes an unusually fast rise of the exchange anisotropy field and coercivity and promotes easy-axis switching to the out-of-plane direction.

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