Stability Of Nanocrystals Research Articles

Formulation of olanzapine nanosuspension based orally disintegrating tablets (ODT); comparative evaluation of lyophilization and electrospraying process as solidification techniques

Olanzapine (OLAN) as an antipsychotic agent has shown its potential in effective management of psychotic disorders however its use is limited because of its poor water solubility. The aim of present work was to improve solubility of OLAN by developing a stable nanocrystal based orally disintegrating tablets (ODTs), using hyperomellose as potential stabilizer. Comparative evaluation of electrospraying and lyophilization as solidification techniques was carried out to assess its effect on solid state properties of OLAN nanocrystals before transformation to ODTs.OLAN Nanosuspension was developed using antisolvent precipitation method and exhibited particle size, polydispersity index and zetapotential value of 223.1 ± 1.5 nm, 0.105 ± 0.4 and −17.9 ± 3.5 mV respectively. Solid powders obtained from both the solidification techniques were compared in terms of size after re-dispersion, particle morphology, surface area, pore volume and solid state of drug present. Subsequently ODTs were prepared from these powders with needful excipients and % amount dissolved was evaluated. Rate of dispersion was found to be higher for ODTs prepared using lyophilized powder (∼84% in 5 min) while other characterization parameters were comparatively similar. Overall, Lyophilization resulted in powders with better bulk level properties in comparison to electrospraying process.

Emergence of intraband transitions in colloidal nanocrystals [Invited

The chemistry of nanocrystals enables the receipt of semiconductor nanoparticles with tunable optical properties. So far most scientific efforts have been focused on wide band gap materials to achieve a bright luminescence and a higher solar power conversion efficiency. Their properties in the infrared range of wavelengths are interesting as well. Two strategies can be used to achieve mid-infrared (mid-IR) transition, either interband transition in narrow band gap material or intraband transition in doped material. In this review, we discuss recent progress to achieve stable doped nanocrystals. We focus on mercury chalcogenide compounds since they are so far the only materials that combine mid-IR absorption with photoconductive properties in this range of energies. We discuss the origin of the doping and its tunability as well as how the doping impacts the optical, transport, and photodetection properties. Finally, we discuss Hg-free alternative materials, and present mid-IR transitions.

General Strategy for the Preparation of Stable Luminous Nanocomposite Inks Using Chemically Addressable CsPbX3 Peroskite Nanocrystals

The potential optoelectronic applications of perovskite nanocrystals (NCs) are primarily limited by major material instability arising from the ionic nature of the NC lattice. Herein, we introduce a facile and effective strategy to prepare extremely stable CsPbX3 NC–polymer composites. NC surfaces are passivated with reactive methacrylic acid (MA) ligands, resulting in the formation of homogeneous nanocubes (abbreviated as MA-NCs) with a size of 14–17 nm and a photoluminescence quantum yield above 80%. The free double bonds on the surface then serve as chemically addressable synthetic handles, enabling UV-induced radical polymerization. Critically, a bromide-rich environment is developed to prevent NC sintering. The composites obtained from copolymerizing MA-NCs with hydrophobic methyl methacrylate and methacrylisobutyl polyhedral oligomeric silsesquioxane monomers exhibit enhanced properties compared to previously reported encapsulated NCs, including higher quantum yields, remarkable chemical stability t...

Cellulose nanocrystals modified with a triazine derivative and their reinforcement of poly(lactic acid)-based bionanocomposites

In order to improve the thermal stability of cellulose nanocrystals (CNCs) and to weaken their hydrophilicity, extensive research has been conducted to graft hydrophobic molecular chains on CNC surfaces to cover and/or replace hydroxyl and sulfate ester groups. According to our previous research, it was proposed that triazine derivative is an ideal candidate to modify CNCs. In this study, triazine derivative-grafted CNCs were synthesized and incorporated into poly(lactic acid) (PLA) nanocomposites as a reinforcing filler. The synthesis of triazine derivative was confirmed by FT-IR and the characterization of modified CNCs was determined by TEM, FT-IR,13C NMR, EDX, TGA and contact angle measurements. It was found that the triazine derivative was successfully grafted onto the CNC surfaces. The thermal stability of the modified CNCs was improved, and hydrophobic CNCs were obtained. Moreover, the properties of CNC/PLA composites were investigated by SEM, UV–Vis spectrophotometer and DSC, and the mechanical properties of composites were measured. The compatability of the modified CNCs with the PLA matrix was improved, and the mechanical properties of PLA composites were improved without serious destruction of their transmittance.

Thermal stability of cellulose nanocrystals prepared by succinic anhydride assisted hydrolysis

A variety of techniques have recently been developed that enable manufacturing of cellulose nanomaterials with optimal properties for certain applications. Acid catalyzed hydrolysis is currently the most popular method for the synthesis of cellulose nanocrystals (CNCs). However, the type of acids and hydrolysis conditions influence the CNCs thermal stability which is crucial parameter in polymer composite technology. In this work thermally stable CNCs were prepared by two step method − (i) hydrolysis in phosphoric acid solutions to produce fine microcrystalline cellulose (MCC), (ii) followed by modification of MMC with succinic anhydride (SA). The method allowed manufacturing CNC-SA material that showed higher thermal stability than the reference cellulose material (UFC-raw) both in the inert gas and air atmosphere. The kinetic parameters of the thermal degradation process of produced cellulose materials were determined by Friedman and Ozawa-Flynn-Wall model-free methods and compared with CNCs prepared in sulfuric acid. On the basis of changes of apparent activation energy Ea a plausible mechanism of stabilization was discussed. The presented results showed the technological potential of organic acid anhydride application for manufacturing and thermal stabilization of CNCs.

Dexibuprofen nanocrystals with improved therapeutic performance: fabrication, characterization, in silico modeling, and in vivo evaluation.

BackgroundThe aim of this study was to prepare and evaluate the impact of polymers on fabricating stable dexibuprofen (Dexi) nanocrystals with enhanced therapeutic potential, using a low energy, anti-solvent precipitation method coupled with molecular modelling approach.MethodsDexi nanocrystals were prepared using antisolvent precipitation with syringe pump. Crystallinity of the processed Dexi particles was confirmed using differential scanning calorimetry and powdered X-ray diffraction and transmission electron microscopy. Dissolution of Dexi nanocrystals was compared with raw Dexi and marketed tablets. Molecular modelling study was coupled with experimental studies to rationalise the appropriate polymers for stable Dexi nanocrystals. Antinociceptive study was carried out using balb mice.ResultsCombinations of hydroxypropyl methylcellulose (HPMC)–polyvinyl pyrrolidone (PVP) and HPMC–Eudragit (EUD) were shown to be very effective in producing stable Dexi nanocrystals with particle sizes of 85.0±2.5 nm and 90±3.0 nm, and polydispersity of 0.179±0.01, 0.182±0.02, respectively. The stability studies conducted for 90 days demonstrated that nanocrystals stored at 2°C–8°C and 25°C were more stable than those at 40°C. The maximum recovery of Dexi nanocrystals was observed from the formulations using the combination of HPMC–PVP and HPMC–EUD, which equated to 98% and 94% of the nominal active drug content respectively. The saturation solubility of the Dexi nanocrystals was substantially increased to 270.0±3.5 μg/mL compared to the raw Dexi in water (51.0±2.0 μg/mL) and stabilizer solution (92.0±3.0 μg/mL). Enhanced dissolution rate (P<0.05) was observed for the Dexi nanocrystals compared to the unprocessed drug substance and marketed tablets. Dexi nanocrystals produced the analgesic effect at much lower doses (5 mg/kg) than that of control standard, diclofenac sodium (20 mg/kg) and Dexi counterparts (40 mg/kg).ConclusionHPMC-PVP and HPMC-EUD were found the best polymer combination to stabilise Dexi nanocrystals. The Dexi nanocrystals exhibited significant dissolution, solubility and analgesic effect compared to the raw Dexi and the control standard diclofenac sodium.

Simultaneous improvement of thermal stability and redispersibility of cellulose nanocrystals by using ionic liquids

Cellulose nanocrystals (CNCs) are predominantly obtained by the traditional sulfuric acid hydrolysis process. However, as-prepared CNCs powder features low thermal stability and poor redispersibility due to the existence of sulfonate groups and the hydrogen bond interaction among particles. Herein, by mixing the ionic liquid [BMIm][BF4] with freshly prepared CNCs without dialysis through a simple rotary evaporate procedure, the simultaneous improvement of thermal stability and redispersibility of CNCs has been achieved. By combining FTIR, TGA and DLS measurements, the critical role of rotary evaporates process for improving the thermal stability of CNCs has been discussed. Furthermore, the poly(lactic acid) (PLLA)/IL-CNC nanocomposites with enhanced mechanical properties were prepared by the melt-mixing method. This study provides a green and simple strategy for preparing dried CNC powders, which has a great potential in large-scale production of fully bio-based nanocomposites.

Water-Assisted Size and Shape Control of CsPbBr3 Perovskite Nanocrystals.

Lead-halide perovskites are well known to decompose rapidly when exposed to polar solvents, such as water. Contrary to this common-place observation, we have found that through introducing a suitable minor amount of water into the reaction mixture, we can synthesize stable CsPbBr3 nanocrystals. The size and the crystallinity, and as a result the band gap tunability of the strongly emitting CsPbBr3 nanocrystals correlate with the water content. Suitable amounts of water change the crystallization environment, inducing the formation of differently shaped perovskites, namely spherical NCs, rectangular nanoplatelets, or nanowires. Bright CsPbBr3 nanocrystals with the photoluminescence quantum yield reaching 90 % were employed for fabrication of inverted hybrid inorganic/organic light-emitting devices, with the peak luminance of 4428 cd m-2 and external quantum yield of 1.7 %.

Ligand-Free Nanocrystals of Highly Emissive Cs4PbBr6 Perovskite

Although ligands of long carbon chains are very crucial to form stable colloidal perovskite nanocrystals (NCs), they create a severe barrier for efficient charge injection or extraction in quantum-dot-based optoelectronics, such as light emitting diode or solar cell. Here, we report a new approach to preparing ligand-free perovskite NCs of Cs4PbBr6, which retained high photoluminescence quantum yield (44%). Such an approach involves a polar solvent (acetonitrile) and two small molecules (ammonium acetate and cesium chloride), which replace the organic ligand and still protect the nanocrystals from dissolution. The successful removal of hydrophobic long ligands was evidenced by Fourier transform infrared spectroscopy, ζ potential analysis, and thermogravimetric analysis. Unlike conventional perovskite NCs that are extremely susceptible to polar solvents, the ligand-free Cs4PbBr6 NCs show robust resistance to polar solvents. Our ligand-free procedure opens many possibilities not only from a material hybridi...

Water‐Assisted Size and Shape Control of CsPbBr3 Perovskite Nanocrystals

AbstractLead‐halide perovskites are well known to decompose rapidly when exposed to polar solvents, such as water. Contrary to this common‐place observation, we have found that through introducing a suitable minor amount of water into the reaction mixture, we can synthesize stable CsPbBr3 nanocrystals. The size and the crystallinity, and as a result the band gap tunability of the strongly emitting CsPbBr3 nanocrystals correlate with the water content. Suitable amounts of water change the crystallization environment, inducing the formation of differently shaped perovskites, namely spherical NCs, rectangular nanoplatelets, or nanowires. Bright CsPbBr3 nanocrystals with the photoluminescence quantum yield reaching 90 % were employed for fabrication of inverted hybrid inorganic/organic light‐emitting devices, with the peak luminance of 4428 cd m−2 and external quantum yield of 1.7 %.

Synthesis of highly efficient and stable CH3NH3PbBr3 perovskite nanocrystals within mesoporous silica through excess CH3NH3Br method

Templated synthesis of CH3NH3PbBr3 perovskite nanocrystals is facile, high-yield, ligand-free, and is another effective method aside from the colloidal method. However, the quantum yield (QY) is still inferior to that of the colloidal synthesized ones. In this report, we show that CH3NH3PbBr3 nanocrystal within mesoporous silica with QY of 75% and full width at half-maximum (FWHM) of 22 nm are obtained through manipulating the molar ratio of CH3NH3Br versus PbBr2 in precursor solution. It is found that excess CH3NH3Br can passivate the surface trap states, reduce nanocrystal size and narrow down the size distribution effectively. These features contribute to the rising of QY, blue-shifting of emission maximum and narrowing down of FWHM. The influence of excess CH3NH3Br can be interpreted in terms of enrichment on the interface of solvent/air because of amphipathy. Moreover, these CH3NH3PbBr3 - mesoporous silica composites present good stability. They preserve 90% of its initial QY after a storage in wet weather with relative humidity of 70 ± 5% for 3 months. The synthesis method proposed in this research provides an effective way to achieve perovskite nanocrystals within mesoporous silica with high efficiency and stability.

Synthesis and Photocatalytic Application of Stable Lead-Free Cs2 AgBiBr6 Perovskite Nanocrystals.

Lead halide perovskite nanocrystals (NCs) have demonstrated great potential as appealing candidates for advanced optoelectronic applications. However, the toxicity of lead and the intrinsic instability toward moisture hinder their mass production and commercialization. Herein, to solve such thorny problems, novel lead-free Cs2 AgBiBr6 double perovskite NCs fabricated via a simple hot-injection method are reported, which exhibit impressive stability in moisture, light, and temperature. Such materials are then applied into photocatalytic CO2 reduction, achieving a total electron consumption of 105 µmol g-1 under AM 1.5G illumination for 6 h. This study offers a reliable avenue for Cs2 AgBiBr6 perovskite nanocrystals preparation, which holds a great potential in the further photochemical applications.

Enhancing Docetaxel Delivery to Multidrug-Resistant Cancer Cells with Albumin-Coated Nanocrystals.

Intravenous delivery of poorly water-soluble anticancer drugs such as docetaxel (DTX) is challenging due to the low bioavailability and the toxicity related to solubilizing excipients. Colloidal nanoparticles are used as alternative carriers, but low drug loading capacity and circulation instability limit their clinical translation. To address these challenges, DTX nanocrystals (NCs) were prepared using Pluronic F127 as an intermediate stabilizer and albumin as a functional surface modifier, which were previously found to be effective in producing small and stable NCs. We hypothesize that the albumin-coated DTX NCs (DTX-F-alb) will remain stable in serum-containing medium so as to effectively leverage the enhanced permeability and retention effect. In addition, the surface-bound albumin, in its native form, may contribute to cellular transport of NCs through interactions with albumin-binding proteins such as secreted protein acidic and rich in cysteine (SPARC). DTX-F-alb NCs showed sheet-like structure with an average length, width, and thickness of 284 ± 96, 173 ± 56, and 40 ± 8 nm and remained stable in 50% serum solution at a concentration greater than 10 μg/mL. Cytotoxicity and cellular uptake of DTX-F-alb and unformulated (free) DTX were compared on three cell lines with different levels of SPARC expression and DTX sensitivity. While the uptake of free DTX was highly dependent on DTX sensitivity, DTX-F-alb treatment resulted in relatively consistent cellular levels of DTX. Free DTX was more efficient in entering drug-sensitive B16F10 and SKOV-3 cells than DTX-F-alb, with consistent cytotoxic effects. In contrast, multidrug-resistant NCI/ADR-RES cells took up DTX-F-alb more than free DTX with time and responded better to the former. This difference was reduced by SPARC knockdown. The high SPARC expression level of NCI/ADR-RES cells, the known affinity of albumin for SPARC, and the opposing effect of SPARC knockdown support that DTX-F-alb have exploited the surface-bound albumin-SPARC interaction in entering NCI/ADR-RES cells. Albumin-coated NC system is a promising formulation for the delivery of hydrophobic anticancer drugs to multidrug-resistant tumors.

Highly Luminescent CsPbX3 (X=Cl, Br, I) Nanocrystals Achieved by a Rapid Anion Exchange at Room Temperature.

Cesium lead halide perovskite (CsPbX3 ) nanocrystals (NCs) exhibit an excellent photoelectric performance, which is directly governed by fine-tuning of the composition and preparation of materials with a special phase structure and morphology. However, it is still facing challenges to achieve highly stable and luminescent CsPbX3 NCs at room temperature. Herein, we report on a novel exchange reaction, in which metal halides MX2 (M=Zn, Mg, Cu, or Ca; X=Cl, Br, or I) solids act as anion source to directly prepare CsPbX3 NCs at room temperature without any pretreatment. Introducing small amount of oleic acid or oleylamine speed up the exchange reaction through different promotion mechanisms. Oleic acid coordinates to the surface of the NCs, which increases the reaction activity, and oleylamine greatly enhances the dissolution of ZnCl2 . XRD and TEM tests demonstrate that the cubic phase structure and the morphology of the parent CsPbX3 were well preserved. Moreover, the band-gap energies and photoluminescence (PL) spectra were readily tunable over the entire visible spectral region of λ=406-685 nm. Our findings could open up the possibilities of using metal halide solids as new anion sources to prepare high-quality CsPbX3 NCs at room temperature.

Enhanced photoluminescence stability of CdS nanocrystals through a zinc acetate reagent.

In this study, the role of a zinc acetate precursor in improving the luminescence stability of purple-emitting CdS nanocrystals is investigated. The oleate-capped core of CdS nanocrystals exhibits intense photodarkening under prolonged UV excitation. From the results of photoluminescence experiments, we can observe that photobleaching is responsible for the degradation of temporal stability, i.e., decline in photoluminescence intensity. Herein, we demonstrate that by adding zinc acetate to the synthesis solution, one can enhance the photoluminescence stability by the complete suppression of the bleaching processes of nanocrystals. We can distinguish between the effects caused by zinc ions and those caused by acetate ligands. Acetate ligands improve the photoluminescence stability of the core of CdS nanocrystals. However, only when zinc acetate is used, the PL stability can be conserved at high excitation power. Simultaneously, we have studied the influence of zinc cations and acetate ligands on the kinetics of nanocrystal growth. The presented results underline the importance of short surface capping ligands and zinc cations in CdS nanocrystal synthesis. This study exhibits a new advantage of exploiting zinc acetate reagents in one-pot nanocrystal synthesis.

Determination of quantum yields of semiconductor nanocrystals at the single emitter level via fluorescence correlation spectroscopy.

Comparing the photoluminescence (PL) properties of ensembles of nanocrystals like semiconductor quantum dots (QDs) with single particle studies is of increasing interest for many applications of these materials as reporters in bioimaging studies performed under very dilute conditions or even at the single particle level. Particularly relevant is here the PL quantum yield (ΦF), which determines the signal size together with the reporter's molar extinction coefficient and is a direct measure for nanocrystal quality, especially for the inorganic surface passivation shell and its tightness, which can be correlated also with nanocrystal stability and the possible release of heavy metal ions. Exemplarily for red and green emitting CdTe nanocrystals, we present a method for the determination of ΦF of nanoparticle dispersions at ultralow concentration compared to cuvette measurements using fluorescence correlation spectroscopy (FCS), a single molecule method, and compared to molecular dyes with closely matching spectral properties and known ΦF. Our results underline the potential of this approach, provided that material-inherent limitations like ligand- and QD-specific aggregation affecting particle diffusion and QD drawbacks such as their complex and power-dependent blinking behavior are properly considered as shown here.

Yb3+ and Yb3+/Er3+ Doping for Near-Infrared Emission and Improved Stability of CsPbCl3 Nanocrystals.

Lead halide perovskite nanocrystals (NCs) exhibit excellent tunable emissions covering the entire visible spectral region, but they do not emit near-infrared (NIR) light. We synthesized rare earth element doped CsPbCl3 NCs for NIR emission. The Yb3+ doped CsPbCl3 NCs emitted strong 986 nm NIR light; the Yb3+/Er3+ co-doped CsPbCl3 NCs emitted at 1533 nm. The total photoluminescence quantum yield (PL QY) of the CsPbCl3 NCs changed from 5.0% to 127.8% upon incorporating 2.0% Yb3+, a factor of 25.6 times enhancement. The material's stability was tested under continuous ultraviolet (365 nm) irradiation. The doped CsPbCl3 NCs exhibited a better stability than the undoped one. The PL intensity of the undoped CsPbCl3 NCs dropped to 20% of the initial value in 27 h, while the doped one took 85 h.

Effect of diphenylphosphinic acid on cesium lead iodide perovskite stability

A contribution to solving challenges in the stability of perovskite nanocrystals by using DPPA in BE so that they can fully be utilized for many applications such as in the field of green energy.

Stable DHLA-PEG capped PbS quantum dots: from synthesis to near-infrared biomedical imaging.

The short shelf-life of water-soluble quantum dots (QDs) due to colloidal instability represents a major drawback to their exploitation. This work examines the colloidal stability of PbS nanoparticles capped with dihydrolipoic acid-polyethylene glycol (DHLA-PEG) ligands terminated with functional groups such as -NH2, -COOH, OMe and -N3. and their application for in vivo imaging. We prove a mechanism of colloidal instability and develop a strategy to produce for the first time stable PEG-capped PbS quantum dots with high quantum yield and optical emission in the first and the second near-infrared (NIR) windows of low absorption of biological tissues. The NIR imaging of in vivo biodistribution is demonstrated at wavelengths >1000 nm, with benefits of reduced tissue absorption and light scattering. The stability, biocompatibility and potential for further QD functionalization open up realistic prospects for non-invasive bioimaging applications.

Highly photoluminescent and stable silicon nanocrystals functionalized via microwave-assisted hydrosilylation.

Herein, we report a microwave-assisted hydrosilylation (MWH) reaction for the surface passivation of silicon nanocrystals (Si-NCs) with linear alkenes. The MWH reaction requires only 20 minutes and allows us to produce Si-NCs with high photoluminescence quantum yields (PLQYs), reaching 39% with an emission maximum of 860 nm. Furthermore, we investigated the effect of ligand length on the photoluminescence properties of Si-NCs. We tested six alkenes with an even number of carbon atoms (from hexene-1 to hexadecene-1). The highest PLQY combined with a long stability (test period of 6 months) was observed when capping with the shortest ligand, hexene-1. The use of microwave heating turns the hydrosilylation step into a facile and sustainable process. In order to provide insight into the emissive properties of Si-NCs surface oxidation and luminescence decay were investigated using Fourier-transform infrared spectroscopy and time-resolved photoluminescence measurements.