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We report on the growth of metal- and metal-oxide based nanoparticles (NPs) in heated polyol solutions. For this purpose, NPs are produced by the sputtering of a silver, gold, or a copper target to produce either silver, gold, or copper oxide NPs in pentaerythritol ethoxylate (PEEL) which has been annealed up to 200 °C. The objective of the annealing step is the fine modulation of their size. Thus, the evolution of the NP size and shape after thermal annealing is explained according to collision/coalescence kinetics and the affinity between the metal-/metal-oxide and PEEL molecule. Moreover, highlights of few phenomena arising from the annealing step are described such as (i) the reduction of copper oxide into copper by the polyol process and (ii) the effective formation of carbon dots after annealing at 200 °C.

Discussion on the synthesis of nanostructures

Made available in DSpace on 2020-12-12T02:36:22Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-05-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Herein we report the synthesis of highly-doped silver nanocluster in fluorophosphate glasses through the melting-quenching method in order to achieve sensitization with Tm3+ and Mn2+ ions. Blue and red emission belonging to Tm3+ (470 to 490 nm) and Mn2+ (550 to 750 nm) ions could be obtained via non-resonant excitation of Tm3+ and Mn2+. Slight decrease of the fluorescence decay times confirmed an energy transfer as a possible mechanism to explain the Tm3+ and Mn2+ emission. The composition of 5 mol% of AgNO3, 0.4 mol% of Tm2O3 and 0.2 mol% of MnF2 in our sample leads to distance between donor (silver nanoclusters) and acceptor (Tm3+-Mn2+) as short as 11 Å, which suggests that the main mechanism for blue and red emission from Tm3+ and Mn2+ is Förster Resonance Energy Transfer (FRET). The results presented here show that the studied material has potential application for multicolor generation as luminophore in white light emitting diodes (W-LED). Institute of Chemistry - São Paulo State University - UNESP Department of Chemical Physics and Optics Faculty of Mathematics and Physics Charles University, Ke Karlovu 3 Department of Chemistry and Chemical Engineering Chalmers University of Technology Institute of Chemistry - São Paulo State University - UNESP FAPESP: #2013/07793-6 FAPESP: #2016/16343-2 FAPESP: #2016/16900-9

Silicon nanoparticles as luminescent sensors

We employ time-dependent photoluminescence (PL) and steady-state PL excitation (PLE) measurements to study the size-dependent optical properties of ultrasmall silicon carbide (SiC) nanoparticles (N...

Misfolding of the protein α-synuclein (αSyn) into amyloid fibrils plays a central role in the development of Parkinson's disease. Most approaches for the inhibition of αSyn fibril formation are based on stabilizing the native monomeric form of the protein or destabilizing the fibrillized misfolded form. They require high concentrations of inhibitor and therefore cannot be easily used for therapies. In this work, we designed an inhibitor (Inh-β) that selectively binds the growing ends of αSyn fibrils and creates steric hindrance for the binding of monomeric αSyn. This approach permits the inhibition of fibril formation at Inh-β concentrations (IC50 =850 nm) much lower than the concentration of monomeric αSyn. We studied its kinetic mechanism in vitro and identified the reactions that limit inhibition efficiency. It is shown that blocking of αSyn fibril ends is an effective approach to inhibiting fibril growth and provides insights for the development of effective inhibitors of αSyn aggregation.

Aggregation of neuronal protein α-synuclein leads to the formation of amyloid fibrils, which are associated with the development of Parkinson's disease. The mechanism of α-synuclein pathology is not fully understood and is a subject of active research in the field. To tackle this problem, the fusions of fluorescent proteins to α-synuclein C-terminus are often used in cellular and animal studies. The effects induced by such α-synuclein sequence extension on α-synuclein aggregation propensity are, however, not systematically examined despite the evidence that the negatively charged C-terminus plays a critical role in the regulation of α-synuclein aggregation. In this work, we investigated how the charge and length variations of the C-terminus affect the aggregation propensity of α-synuclein. To address these questions, we prepared mutants of α-synuclein carrying additional moieties of different charge and length at the protein C-terminus. We determined the rates of two different aggregation stages (primary nucleation and elongation) based on a thioflavin T kinetic assay. We observed that all mutants bearing neutrally charged moieties of different length fibrilized slower than wild-type α-synuclein. The primary nucleation and elongation rates strongly decreased with increase of the C-terminal extension length. Meanwhile, charge variation of the C-terminus significantly changed the rate of α-synuclein nucleation, but did not markedly affect the rate of fibril elongation. Our data demonstrate that both the charge and length of the C-terminus play an important role at the stage of initial fibril formation, but the stage of fibril elongation is affected mainly by the length of C-terminal extension. In addition, our results suggest that there are at least two steps of incorporation of α-synuclein monomers into the amyloid fibril: namely, the initial monomer binding to the fibril end (charge-dependent, relatively fast), and the subsequent conformational change of the protein (charge-independent, relatively slow, and thus the rate-limiting step).

Silicon (Si) nanostructures allow for the expansion of the application spectrum of this important semiconductor material with respect to the fields of optoelectronics and photonics. At the same time, the significant potential of Si quantum dots (SiQDs) has been revealed in terms of their potential application in the areas of biology and medicine due to their biocompatibility, low toxicity and natural biodegradability, unlike currently used semiconductor quantum dots. As far as this study is concerned, SiQDs co-doped with boron and phosphorus were used for the in vitro evaluation of their cytotoxicity in human osteoblasts. Two chemically identical types of SiQD differing in terms of their size and photoluminescence (PL) were studied. They both display long-lasting dispersion in methanol and even in aqueous media as well as PL which is not sensitive either to changes in the environment or surface modifications. Our experiments revealed significant differences between the two types of SiQD tested in regard to their behavior in a cell culture environment depending on increasing concentration (25–125 μg ml−1) and cultivation conditions (the presence or absence of proteins from the fetal bovine serum – a component of the cultivation medium). A detailed description of their optical parameters and the evaluation of zeta potential enhance the understanding of the complexities of the in vitro results obtained.

Various porous solid sorbents in the form of powder or monoliths have been developed over the last years, as a promising solution for reducing CO2 emissions. Although powder sorbents, due to higher porosities and efficient mass transport, exhibit higher capacities compared with monoliths, several factors limit their suitability for practical application. The most prominent is their low bulk density, which makes them difficult to handle and poses health risks due to dust inhalation. In this work, we prepared robust hierarchically porous carbon-based monoliths based on a simple three-step approach with the focus on combining efficient CO2 adsorption and transport with easy handling for practical applications. The approach is based on incorporation of polystyrene nanoparticles (PS NPs) and expanded graphite (EG) into a nitrogen-rich precursor, which is polymerized to form 3D monoliths. Incorporation of thermally unstable PS NPs or thermally stable EG enables us to control the formation of macropores during a precarbonization step, while variation of KOH concentration and mixing intensity during a subsequent activation step controls the formation of micropores. The resulting hierarchically porous monoliths with high nitrogen contents exhibited CO2 uptake capacities reaching 6.52 mmol g−1 at 273.15 K and 1 bar, which is among the highest reported for porous carbon monoliths. In addition, the materials also exhibited good reversibility of CO2 adsorption over several cycles with simple regeneration under mild conditions. Considering the high CO2 capture performance together with improvements in sorbent properties such as easy handling and reusability, the presented sorbents are promising candidates for practical applications.

The luminescence linewidth of individual silicon nanocrystals was characterized by single-dot spectroscopy, and an ultranarrow linewidth of similar to 200 mu eV at 10 K was found. This value is, in fact, limited by system resolution and represents only the upper limit of the homogeneous linewidth. In addition, the effect of the matrix was investigated for nanocrystals coated with organic ligands, embedded in silicon dioxide, as well as for nanocrystals with only a thin passivating layer. It was found that, depending on the matrix, the room-temperature bandwidth may vary by an order of magnitude, where values as small as similar to 12 meV (similar to 5 nm) at 300 K were detected for nanocrystals with a thin passivation. The observed values for silicon nanocrystals are similar and even surpass some of those for direct-band-gap quantum dots. The narrow linewidth at room temperature enables the use of silicon nanocrystals for nontoxic narrow-band labeling of biomolecules and for application as phosphors in white-light-emitting devices. QC 20141114

The number of newly developed nanomaterials is steadily increasing but only a few are suitable for applications in biology. These nanomaterials are often made from harmful compounds and there is no convenient technique to remove them from the body after application. This study is focused on silicon nanocrystals and nanodiamonds, which are two promising nanomaterials for bio-applications. Silicon nanocrystals (Si-NCs) are exceptional since they provide several desired properties: low cytotoxicity, suitability for chemical activation, efficient photoluminescence, and bio-degradability. All these parameters promote application of Si-NCs in living organisms and even human medicine. Nanodiamonds (NDs), on the other hand, are non-biodegradable which limits their use to mostly long term in vitro studies. However, when using these nanomaterials one needs to address the effect of accumulation and aggregation of such materials in cells and how it contributes to the overall cytotoxicity. Here, we present studies on the interaction of two promising nanomaterials Si-NCs and NDs with actin structure of mammalian cells, evaluation of their cytotoxicity by various methods, and observation of single nanoparticle luminescence spectra within living cells. According to our results Si-NCs are more promising for application in nanomedicine compared to NDs.

We have prepared colloidal solutions of clusters composed from porous silicon nanoparticles in methanol, water and phosphate-buffered saline (PBS). Even if the size of the nanoclusters is between 60 and 500 nm, due to their highly porous “cauliflower”-like structure, the porous silicon nanoparticles are composed of interconnected nanocrystals having around 2.5 nm in size and showing strong visible luminescence in the orange-red spectral region (centred at 600–700 nm). Hydrophilic behaviour and good solubility of the nanoclusters in water and water-based solutions were obtained by adding hydrogen peroxide into the etching solution during preparation and 16 min long after-bath in hydrogen peroxide. By simple filtration of the solutions with syringe filters, we have extracted smaller nanoclusters with sizes of approx. 60–70 nm; however, these nanoclusters in water and PBS solution (pH neutral) are prone to agglomeration, as was confirmed by zeta potential measurements. When the samples were left at ambient conditions for several weeks, the typical nanocluster size increased to approx. 330–400 nm and then remained stable. However, both freshly filtered and aged samples (with agglomerated porous silicon nanoparticles) of porous silicon in water and PBS solutions can be further used for biological studies or as luminescent markers in living cells.

Boron (B) and phosphorous (P) codoped silicon quantum dots (Si QDs) are dispersible in polar solvents without organic ligands, and exhibit size controllable photoluminescence (PL) from 0.85 to 1.85 eV due to the electronic transitions between the donor and the acceptor states. We study the PL spectra of the codoped Si QDs at room temperature and at 77 K. We show that the broad PL band of codoped colloidal Si QDs (full width at half maximum is over 400 meV) is composed of narrower PL bands of individual QDs with different PL energies. We also show that the PL linewidth of individual codoped Si QDs is almost twice as large as those of undoped Si QDs. In contrast to the significant narrowing of the PL linewidth of undoped Si QDs at low temperatures, that of codoped Si QDs is almost independent of the temperature except for a few very small QDs. These results suggest that a large number of B and P are doped in a QD and there are a number of non-identical luminescence centers in each QD.

The presented work is aimed at the development of nontoxic nanocrystalline silicon fluorescence labels, biodegradable in living body and long-term stable, and of fluorescent nanodiamonds mainly for in vitro use. These novel fluorescence labels could be very good substitutes for commercially used quantum dots (e.g. cadmium compound quantum dots) which can be toxic according to the latest results. In this work, manufacturing of porous nanocrystalline silicon (por-Si) is described, several basic optical properties of por-Si are presented and the influence of Si nanocrystals, nanodiamonds, and milled silicon on the growth of a cell culture of L929 mouse fibroblast and HeLa cells is compared. Bio-interaction of nanoparticles was studied by optical transmission microscopy, time-lapse microphotography of cell culture evolution, fluorescence microscopy, fluorescence microspectroscopy, and scanning electron microscopy. The size and shape of nanocrystals were determined using atomic force microscopy (AFM).

Colloidal suspensions of small silicon nanoparticles (diameter around 2nm) with fast and efficient ultraviolet-blue photoluminescence (PL) band are fabricated by enhanced electrochemical etching of Si wafers. The detailed study of photoluminescence excitation spectra in a wide range of excitation photon energies (270-420nm) reveals specific behavior of the Stokes shift of the fast PL band that agrees well with theoretical calculation of optical transitions in small silicon nanocrystals and is distinct from emission of silicon dioxide defects.