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  • 57 Reads
Assessment of the potential of polymer/HDI-GO nanocomposites for use in organic solar-cells

Conductive films comprising conducting polymers and carbon nanomaterials have gained a lot of interest for applications in several fields, including transparent electrodes, supercapacitors, light-emitting diodes (LEDs), polymer solar cells (PSCs), and so forth. One of the main motivations is the replacement of costly oxides and degradable materials, like indium tin oxide (ITO). On the other hand, graphene oxide (GO) has emerged as an ideal filler to reinforce polymeric matrices owing to its large specific surface area, transparency, flexibility, and very high mechanical strength. Nonetheless, functionalization is required to improve its solubility in common solvents and expand its practical uses. In this work, the potential of polymer nanocomposites based on hexamethylene diisocyanate (HDI)-functionalized GO (HDI-GO)/ poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS) for use as active layers (ALs) or interfacial layers (IFLs) in PSCs has been assessed. Conventional deposition techniques applied to thin films were tested for the developed nanocomposites. Deposition methods included drop and spin casting, where different type of substrates, as clean glass and glass/ITO were tested. The results of deposition essays were analyzed by atomic force microscopy (AFM) and UV-vis spectra. In addition, thermal evaporation was tried with the aim to obtain homogeneous layers. The layers obtained by drop casting showed poor film quality, with large aggregates. On the other hand, spin coating lead to layers not fully wetting the substrate. New synthesis procedures for the nanocomposites and/or alternative treatments of substrate surface will be investigated in the future to optimize their composition and properties (ie. transparency) and improve their suitability for use in PSCs.

  • Open access
  • 56 Reads
Four-Wave Mixing in Asymmetric Double Quantum Dot Molecule – Metal Nanoparticle Assemblies

The coupling between excitonic and plasmonic nanoparticles produces collective optical properties, which are quite different from the properties of the individual components, leading to modification of the optical properties, such as the emission, the dispersion and the absorption, of hybrid quantum dot-plasmonic nanoparticle structures. During the last years, these interesting optical effects have attracted the scientific interest, both on an experimental, as well as, on a theoretical level, in hybrid nanostructures which are composed of semiconductor quantum dots and metal nanoparticles. The study of the Λ-type system that describes the asymmetric double- semiconductor quantum dot system (asymmetric quantum dot molecule) has also attracted the scientific interest of several scientists, who investigated various effects, including the pump-probe response and the four-wave mixing, as well as, the Autler-Townes splitting and the tunneling-induced transparency effects. In this study, the four-wave mixing spectrum of a strongly pumped hybrid structure is theoretically examined. The hybrid structure consists of an asymmetric double semiconductor quantum dot molecule and a spherical metal nanoparticle, which are coupled together via long-range Coulomb interaction. Having as a starting point the Hamiltonian of the system, in the dipole and the rotating-wave approximations, we derive a set of nonlinear density matrix equations, which are numerically solved, in the steady-state limit, and then the four-wave mixing coefficient is calculated within a range of values of the pump-probe field detuning. The spectral response of the four-wave mixing coefficient is investigated, for different values of the pump-field detuning, the electron-tunneling rate and the energy gap between the upper states in the energy-level scheme of the double semiconductor quantum dot molecule, while the interparticle distance between the two components of the structure is modified.

  • Open access
  • 76 Reads
A Gold Nanoparticle Nanonuclease Relying on a Zn(II) Mononuclear Complex

Despite being the fundament of life for living organisms, many functionalities of DNA and RNA still present as challenging targets for scientists. One such aspect is the elucidation of the complete mechanism behind the hydrolysis of the nucleic acids’ backbone, comprised of repeated phosphodiester bond segments linking adjacent nucleosides. Indeed, the phosphate bond is known for its superb stability, which allows RNA and DNA to remain intact at 25°C, pH 7.0 for hundreds and millions of years, respectively. However, enzymes called nucleases perform the phosphodiester cleavage in seconds, a result yet to be surpassed by artificial competitors.

To date, not even the most meticulously designed molecules have approached the efficiency demonstrated by nucleases and researchers are still trying to understand the underlying hydrolytic mechanisms behind these enzymes. Accordingly, we decided to challenge ourselves with that issue and by using the principles of nano and supramolecular chemistry we attempted to reach enzymes’ efficacy and elucidate the mechanism of phosphodiester cleavage.

In our recent work we reported surface-passivated gold nanoparticles behaving like artificial nanonucleases, cleaving plasmid DNA pBR322 with the highest efficiency reported thus far based on a single metal ion mechanism.1 Inspired by nature’s nucleases, we created a pocket comprising one Zn(II) ion, one arginine and one serine, precisely mimicking the active site suggested for natural metallonucleases grounding their efficiency on a monometallic mechanism. Experimental studies supported by MD calculations revealed a key role of a positively charged arginine, which assists in the transition state stabilization and reduces the pKa of the nucleophilic alcohol of serine, followed by one Zn(II) ion coordinating a phosphate diester of DNA.

Our additional studies performed with commonly used DNA model BNP (bis-p-nitrophenyl phosphate) demonstrated how by designing an artificial catalyst just based on experiments with a simple model substrate can lead to misguided conclusions when compared with a real target such as plasmid DNA.

1. Scrimin, P. M.; Czescik, J.; Zamolo, S.; Darbre, T.; Rigo, R.; Sissi, C.; Pecina, A.; Riccardi, L.; De Vivo, M.; Mancin, F., A Gold Nanoparticle Nanonuclease Relying on a Zn(II) Mononuclear Complex. Angewandte Chemie International Edition (just accepted); doi: 10.1002/anie.202012513

  • Open access
  • 86 Reads
HOXB7 siRNA delivered by hybrid nanoparticles and the co-therapy with tamoxifen: promising strategy against hormone receptor positive breast cancer

Breast cancer is the most common type of cancer that affects and kills women annually in the world. It affects more than two million women and is responsible for the death of approximately 25% of them. Almost 70% of breast cancer diagnosis are positive for hormone receptor and have a good prognosis. However, resistance to drugs used in hormone therapy, such as tamoxifen, is usual and about 40% of recurrences do not respond to it. In some cases, the overexpression of HOXB7 gene is related to this mechanism and its silencing can reverse the response to tamoxifen. Here we used copolymer-coated calcium phosphate nanoparticles to deliver HOXB7 siRNA and restore the sensitization of MCF7 cells to tamoxifen. Nanoparticle synthesis and characterization were performed and cell viability and gene expression were evaluated. Hybrid nanoparticle presented Z-average diameter of 88nm and PdI of 0.1, while showing good entrapment of siRNA molecules. We also observed a decrease in HOXB7 gene expression (~65%) promoted by the siRNA molecule delivered by the nanoparticles. The gene silencing has good correlation to the cell viability assay: a reduction in breast cancer viability was observed in 48 (31%) and 72 (38%) hours. As for the co-treatment with tamoxifen, cell viability started dropping after 15 hours, which did not occur in the treatment only with tamoxifen at the same concentration. This result indicates that the biological effect was possibly related to RNAi effect and suggests that HOXB7 may be promoting cell sensitization to tamoxifen without reducing cell viability. Also, we found that the IC50 of tamoxifen was reduced by about 25% of initial dose when sensitizing MCF7 cells (co-treatment). Overall, these results suggest that the nanoparticles were effective in promoting gene silencing and that the co-therapy can be a promising tool for the treatment of hormone receptor positive breast cancers.

  • Open access
  • 5712 Reads
Removal of Manganese using Polymer gel composites

Manganese is the biggest concern in Bangladesh after Arsenic, as almost 50% area contain groundwater with Mn concentrations greater than the WHO drinking water guidelines. The previous studies suggested that ᵧ-FeOOH could remove Mn effectively from water. However, those studies were conducted at higher pH levels and not in natural conditions. Also, the practical applicability of the Mn removal methods was not discussed. Because additional separation processes required to separate the adsorbents and precipitations are not environmentally friendly. Therefore, to improve the Mn removal efficiency at natural pH levels and other natural water conditions, we examined Mn removal by adsorption technology using polymer gel composites. The gel composites were a cationic gel composite, N,N-Dimethylamino Propylacrylamide, methyl chloride quaternary (DMAPAAQ), loaded with iron hydroxide (DMAPAAQ+FeOOH), and a non-ionic gel composite, N, N- Dimethylacrylamide (DMAA), loaded with iron hydroxide (DMAA+FeOOH). DMAPAAQ+FeOOH gel contains 62.01 wt% of ᵧ-FeOOH in its polymer structures because of the unique preparation method and also this gel showed better As removal efficiency than the other adsorbents at natural conditions ensuring it’s environmental friendliness. Our results suggest that the cationic gel composite, DMAPAAQ+FeOOH, removed Mn more than that of DMAA+FeOOH because the content of ᵧ-FeOOH particles were higher in the gel structure of DMAPAAQ+FeOOH. Although the polymer component of DMAPAAQ+FeOOH did not contribute to the adsorption of Mn, it carried the higher amount of ᵧ-FeOOH components, which helped to remove Mn. Our results also suggested that the presence of As did not have any effect on the adsorption of Mn with DMAPAAQ+FeOOH gel composite. Because the polymeric component (DMAPAAQ) adsorbed As and the ᵧ-FeOOH particles adsorbed Mn, which provides the basis for simultaneous adsorption of As and Mn. This research is a base for the simultaneous removal of harmful components such as As, Mn, Cr, Cd, and more.

  • Open access
  • 47 Reads
Fluorescent chitosan nanogels developed for targeting endothelial cells of axillary lymph nodes

Nanogels are a novel class of three-dimensional cross-linked polymers able to retain high amounts of water in their network structure, with large potential applications in nanomedicine. In our study, the polymer matrix selected was chitosan, as this polysaccharide biopolymer composed of N-acetylglucosamine and glucosamine residues exhibit great biocompatibility and low toxicity. The preparation was performed by ionic gelation in the presence of hyaluronic acid and sodium tripolyphosphate, having rhodamine or fluorescein isothiocyanate molecules grafted on chitosan backbone. In order to validate the possible usage of these chitosan-fluorophores conjugates for fluorescence imaging purposes in cancer diagnostics and therapy, their biological effect was assessed on SVEC4-10 cells (a simian virus 40-transformed mouse microvascular endothelial cell line). Cell viability, membrane integrity and nanogels uptake were examined following the exposure for 6 and 24 hours at concentrations up to 120 µg/mL. A good biocompatibility was obtained after both time intervals of incubation with nanogels, as no increase in cell death or membrane damage being noticed compared to control. By examination on confocal laser scanning microscopy, the both types of fluorescent nanogels agglomerated on the surface of cell membrane, their cellular internalization being observed only for few cells, preferentially at the cell periphery. In conclusion, based on the biocompatibility of the nanogels, these can further incorporate gadolinium for an improved magnetic resonance Imaging effect in nanomedicine.

Acknowledgments This work was supported by a grant of the Romanian Ministry of Research and Innovation, CCCDI - UEFISCDI, project number PN-III-P3-3.1-PM-RO-FR-2019-0204 / 6 BM/ 2019, within PNCDI III.

  • Open access
  • 75 Reads
Formation, Phase Composition and Memristive Properties of Titanium Oxide Nanodots

The increase in the modern electronics productivity is limited by the CMOS structures minimum size. Further miniaturization is impossible due to an increase in leakage current. Therefore, increasingly attention is paid to the development and research of new nanoelectronic elements with small characterizing dimensions, as well as high performance and speed. In this case, the resistive switching effect is achieved due to the formation of oxide nanostructures with a controlled stoichiometric composition. The local anodic oxidation method is the most promising method for memristor formation since the resulting structures exhibit the forming-free memristor effect and can be used as memory elements, as well as for performing logical operations. In this work, the titanium oxide nanodots arrays formation was carried out at various parameters and the structures geometric dimensions dependences on the applied voltage amplitude and duration pulse were obtained. A current-voltage characteristics study of nanodots showed that the resulting structures switch between the high(140 GΩ) and low(1.7 GΩ) resistance states. Furthermore, we performed a numerical simulation of the formation of oxide nanodots obtained by the local anodic oxidation method, the results of which showed that the TiO2 phase dominates on the formed oxide surface. As the oxide goes deeper into the bulk, the Ti2O3 and TiO phases appear, and the TiO phase prevails near the metal/oxide interface. To confirm the simulation results, the titanium oxide nanodots phase composition was studied by the XPS method, which confirmed the theoretical results. The results can be used in the development of technological processes for the formation of elements of nanoelectronics, as well as elements of resistive memory based on oxide nanoscale structures. The reported study was funded by RFBR, according to the research project No. 19-29-03041_mk, and by grant of the President of the Russian Federation No. MK-767.2020.8.

  • Open access
  • 56 Reads
Characterization of silicon quantum dots’ properties and kidney toxicity in mice
Published: 11 November 2020 by MDPI in 2nd International Online-Conference on Nanomaterials session Poster

Due to their various optical and electronic features that offer advantages for medical purposes compared to traditional nanoparticles (NPs), quantum dots (QDs) represent an emerging tool for in vivo imaging, tumor biology investigation, and cancer treatment. Notwithstanding, QDs can also trigger toxicity effects in healthy cells, as previously reviewed by Zhu et al. [1]. Given that, we further aimed herein to characterize the silicon-based QDs obtained by laser ablation and evaluate their in vivo kidney toxicity. The studied NPs exhibited at transmission electronic microscope a core-shell structure with a crystalline silicon core and an amorphous silica shell with a diameter ranging between 6 and 10 nm. Their tendency to aggregate led to the formation of aggregates with sizes of hundreds of nanometers. QDs dispersion in water revealed a hydrodynamic diameter around 200 nm and a negative zeta potential of -14 mV. To test their in vivo toxicity, different doses of QDs (0, 1 10 and 100 mg QDs/ kg body weight) prepared in 0.9% saline were injected in the caudal vein of the Swiss mice. The animals were sacrificed at 1, 6, 24 and 72 hours, and the kidney tissue was harvested. The effects of silicon QDs on the antioxidant defense of kidney cells were investigated throughout the assessment of antioxidant enzymes’ activities (catalase, superoxide dismutase, glutathione peroxidase, glutathione reductase and glutathione S-transferase). The administration of the highest dose of QDs induced a significant reduction in catalase activity, the level being half of the control after all periods of exposure. A time-dependent decrease in glutathione reductase activity was noticed for all doses administered compared to control animals. After 24 and 72 h, glutathione peroxidase and glutathione S-transferase were diminished in the kidney cells of mice that received 10 and 100 mg/kg b.w. compared to control, revealing that these enzymes were vulnerable to oxidative damage of high doses of silicon QDs. Yet, no significant changes were observed regarding the activity of superoxide dismutase in the kidney of treated mice compared to control, suggesting that the QDs administration would not generate superoxide anions inside kidney cells. This study highlighted the possible damaging effects of high doses of silicon-based QDs (>10 mg QDs/kg b.w.) on kidney cells, providing useful information for further clinical studies on humans.

  • Open access
  • 86 Reads
Microwave-assisted hydrothermal synthesis of Zn2SnO4 nanostructures for photocatalytic dye degradation

Zinc-tin oxide (ZTO) material system possesses a wide range of attractive properties for a new generation of multifunctional nanodevices. It can crystallize in Zn2SnO4 and ZnSnO3 phases, with different types of nanostructures possible for each phase. Each has unique properties suitable for applications in catalysis, sensors, transistors, memories, or energy harvesting devices [1,2]. In previous works an in-depth study on the influence of the chemico-physical parameters of a seed-layer free hydrothermal synthesis in a conventional oven (24 h at 200 °C) allowed to control the achievement of different types of ZTO nanostructures [3,4]. An alternative route to circumvent the inconveniently long synthesis durations in a conventional oven is the microwave heating assisted synthesis, which allows to achieve accelerated chemical reactions [5]. As such, in this work it is shown that Zn2SnO4 nanoparticles, octahedrons and nanoplates are obtained by microwave-assisted synthesis with reduced processing times of up to 22 h, while still yielding reproducible and homogeneous results. The photocatalytic activity of the Zn2SnO4 nanostructures produced using the microwave system are evaluated for rhodamine B degradation under UV light, being observed a better performance for Zn2SnO4 nanoparticles with >90 % of degradation in 2.5 hours.

  1. A. Rovisco et al., Hydrothermal Synthesis of Zinc-Tin Oxide Nanostructures for Photocatalysis, Energy Harvesting and Electronics, in Novel Materials, IntechOpen, 2020. Accepted
  2. A. Rovisco et al., ACS Appl. Mater. Interfaces 2020, 12, 18421–18430.
  3. A. Rovisco et al., ACS Appl. Nano Mater. 2018, 1, 3986–3997.
  4. A. Rovisco et al., Nanomaterials 2019, 9, 1002.
  5. D. Nunes et al., Catalysis Today 2016, 278, 262-270.
  • Open access
  • 55 Reads
Biocompatibility and cellular uptake of fluorescent chitosan nanohydrogels in murine macrophages and B lymphocytes

Due to their intrinsic viscosity and hydrophilicity, nanohydrogel systems are used to significantly increase the efficiency of commercial contrast agents for MRI and thus effectively improve the sensitivity of the MRI technique. Since chitosan (CS) is a biocompatible polysaccharide frequently used in biomedical applications, we aimed to prepare chitosan nanohydrogels (NGs) by ionic gelation, the polysaccharide being further grafted with rhodamine (RBITC) and fluorescein isothiocyanate (FITC). In this way, the cytotoxic effect of different concentrations (5, 15, 30, 60 and 120 µg/mL) of the fluorescent CS-FITC and CS-RBITC NGs was investigated by assessing the plasma membrane integrity and the metabolic activity of RAW 264.7 murine macrophages and A20 mouse lymphoma B cells following exposure for 6 and 24 hours. The cell viability (MTT assay) and lactate dehydrogenase activity were analyzed by spectrophotometric methods, while cellular uptake was observed by fluorescence microscopy. Our results showed that the exposure to CS-FITC and CS-RBITC NGs for 6 and 24 hours did not induce significant changes to RAW 264.7 and A20 cells compared to control, proving a good nanogel biocompatibility for both cell lines. In addition, the fluorescence microscopy showed that cellular uptake was quite rapid and efficient for the NGs tested. Taking all of these into consideration, we can conclude that all types of nanohydrogels were biocompatible, being internalized in both cell types with predominantly cytoplasmic localization.

Acknowledgments: This work was supported by a grant of the Romanian Ministry of Research and Innovation, CCCDI-UEFISCDI, project number PN III-P3-3.1-PM-RO-FR-2019-0204/6BM/2019, within PNCDI III