Preparation and characterization of hybrid polypyrrole nanoparticles as a conducting polymer with controllable size.

Hybrid polypyrrole (PPy) nanoparticles were prepared using a low-temperature oxidative polymerization process in an acidic solution with polyethyleneimine (PEI) as a template and amine source. The results showed that the nanoparticles have an amorphous structure in the X-ray diffractogram and exhibited good dispersibility in water, uniform size, and a specific conductivity ranging from 0.1 to 6.9 S/cm. The particle size could be tuned from 85 to 300 nm by varying the reactant concentration. Undoping the samples with sodium hydroxide (NaOH) solution altered the optical absorption properties and surface roughness of the particles. However, it did not affect the particle size. The nanoparticles also exhibited optical sensing properties based on their UV-vis absorption changes with the pH. Moreover, nanoparticles could have potential applications in gene delivery and bio-adsorption for contaminant removal. This work demonstrates a simple and effective method for preparing hybrid polypyrrole nanoparticles with controllable size, dispersibility, and conductivity for various nanotechnology, biotechnology, and environmental engineering purposes.

Clay nanotubes as a novel multifunctional excipient for the development of directly compressible diclofenac potassium tablets in a SeDeM driven QbD environment.

Halloysite is a unique biocompatible aluminosilicate clay mineral with powder particles predominantly comprising of concentrically rolled nanotubular aggregates. Some recent studies have also contributed to its prospective case in oral drug delivery and dosage forms albeit with limited commercial viability. In this study, we have investigated the use of halloysite nanotubes (HNTs) as a directly compressible multifunctional tableting excipient using SeDeM diagram expert tool. SeDeM experimentations revealed that ~68% HNTs in the formulations were enough to be used as a directly compressible filler, binder, and disintegrant in diclofenac potassium formulations. In the next phase, a total of 8 formulations blends (IRF1-8) of diclofenac potassium (50 mg) with HNTs and Starch 1500® were prepared in different ratio using simple lattice mixture design and all were found satisfactory for direct compression. Compressed tablets (167 mg) had narrow weight variation (SD = ± 1.78 mg), good hardness (~9-9.5 kg), acceptable friability (<0.7%) and fast disintegration time (<1.5 min). Moreover, the cumulative dissolution at 1 h in phosphate buffer pH 6.8 was found compliant with the compendial criteria (> 92% against 75%). The dissolution profile was best fitted with Peppas-Sahlin model with Fickian diffusion as the only mechanism. f2 similarity test revealed that almost all the tablets were pharmaceutical equivalent to the marketed formulation of the drug. A shelf-life of ~34 months was found upon long-term stability testing of the optimized formulation. This study demonstrates that this novel and economically viable clay material has a strong potential for commercial use in tableting of drug by direct compression.

Exfoliated graphene nanosheets: pH-sensitive drug carrier and anti-cancer activity.

A straightforward and facile method for the exfoliation of graphene sheets using poly(vinylpyrrolidone) nanoparticles of an average size of 42nm was developed and their dual role as pH-sensitive drug carrier and anti-cancer agent was evaluated. The cytotoxic impact of the exfoliated nanosheets (GRP-PVP-NP) was examined on various cells (HCT-116, HeLa, SCC-9, NIH-3T3 and HEK-293cells) by a series of assays. Their cytotoxic nature was attributed to affecting the mitochondrial enzyme activity, proliferation capability, and the formation of tight junctions in cancer cells. The endocytosis was found to be internalization mechanism for the cellular uptake of nanosheets. The generation of reactive oxygen species and elicitation of caspase-3 activity which was undoubtedly associated with triggering of oxidative stress speculated to be the dominant cause of the cytotoxic pattern of nanosheets against cancer cells. Additionally, the results also showed the role of the nanosheets as a pH-sensitive drug carrier through drug loading by supramolecular interaction. The efficient release of doxorubicin was seen at low pH and in an environment with a low oxygen concentration, thus under conditions mimicking the typical tumor microenvironment. Therefore, these findings provide the first evidence for a dual function of exfoliated graphene sheets and also elucidate the cytotoxic mechanism responsible for the cancer cell death.

Protein-coated pH-responsive gold nanoparticles: Microwave-assisted synthesis and surface charge-dependent anticancer activity.

The biocompatibility and ease of functionalization of gold nanoparticles underlie significant potential in biotechnology and biomedicine. Eight different proteins were examined in the preparation of gold nanoparticles (AuNPs) in aqueous medium under microwave irradiation. Six of the proteins resulted in the formation of AuNPs. The intrinsic pH of the proteins played an important role in AuNPs with strong surface plasmon bands. The hydrodynamic size of the nanoparticles was larger than the values observed by TEM and ImageJ. The formation of a protein layer on the AuNPs accounts for this difference. The AuNPs exhibited sensitivity towards varying pH conditions, which was confirmed by determining the difference in the isoelectric points studied by using pH-dependent zeta potential titration. Cytotoxicity studies revealed anticancerous effects of the AuNPs at a certain micromolar concentration by constraining the growth of cancer cells with different efficacies due to the use of different proteins as capping agents. The positively charged AuNPs are internalized by the cells to a greater level than the negatively charged AuNPs. These AuNPs synthesized with protein coating holds promise as anticancer agents and would help in providing a new paradigm in area of nanoparticles.

Double-stranded DNA-graphene hybrid: preparation and anti-proliferative activity.

Herein, we demonstrate a simple method to prepare graphene dispersions in an aqueous solution of DNA by the sonication of bulk graphite. The use of a commercial double-stranded DNA as a stabilizer for graphite exfoliation without any chemical modification is presented. The high energy sound waves cleave a double-stranded DNA into two single-stranded DNAs. UV-vis spectral studies show that the nucleobases in the product are intact. Atomic force microscopy studies reveal that the size of the obtained nanosheets can be enriched into smaller lateral dimensions using centrifugation. Raman spectroscopy suggests that the defects found in the nanosheets induced by the sonication are edge defects, whereas the bodies of the sheets remain relatively defect free. The graphene dispersions are extremely stable over a wide range of pH values, possessing high negative zeta potential values. The anti-proliferative effect observed through in vitro cytotoxicity studies is supported by in vivo studies using the zebrafish human tumor xenograft model. The migration of cancer cells in zebrafish embryos are inhibited by the graphene nanosheet dispersion. The negatively charged nanosheet serves as a platform for the adsorption of gold nanoparticles with positively charged surfaces.

Coupling of carbon and peptide nanotubes.

Two of the main types of nanotubular architectures are the single-walled carbon nanotubes (SWCNTs) and the self-assembling cyclic peptide nanotubes (SCPNs). We here report the preparation of the dual composite resulting from the ordered combination of both tubular motifs. In the resulting architecture, the SWCNTs can act as templates for the assembly of SCPNs that engage the carbon nanotubes noncovalently via pyrene "paddles", each member of the resulting hybrid stabilizing the other in aqueous solution. The particular hybrids obtained in the present study formed highly ordered oriented arrays and display complementary properties such as electrical conductivity. Furthermore, a self-sorting of the cyclic peptides toward semiconducting rather than metallic SWCNTs is also observed in the aqueous dispersions. It is envisaged that a broad range of exploitable properties may be achieved and/or controlled by varying the cyclic peptide components of similar SWCNT/SCPN hybrids.

Synthesis of highly fluorescent gold nanoclusters using egg white proteins.

Gold nanoclusters (AuNCs) have gained interest during the recent years because of their low toxicity and finer size for the bioimaging and biolabeling applications in comparison to the semiconductor quantum dot analogues. Diverse materials such as sulfur compounds, peptides, dendrimers, proteins, etc., are exploited for the preparation of AuNCs. Henceforth, highly fluorescent, water-soluble, and few atom-containing gold nanoclusters are created using a rapid, straightforward, and green method. In this regard for the first time chicken egg white (CEW), one of the most unique materials, is utilized in an aqueous solution under basic conditions at physiological temperature for the preparation of AuNCs. Tyrosine and tryptophan amino acid residues are responsible for the conversion of Au ions to Au(0) under alkaline condtions. CEW contains four major proteins of which the main constituent protein, ovalbumin also leads to the formation of the AuNCs with a higher fluorescence emission compared to the CEW. The ratios between the different reaction partners are very crucial, along with temperature and time for the preparation of AuNCs with high photoluminescence emission. The limited vibrational motion of the proteins under alkaline condition and the bulkiness of the proteins help in the formation of AuNCs.

Cellular interactions of doxorubicin-loaded DNA-modified halloysite nanotubes.

Halloysite nanotube (HNT)-based supramolecular complexes are synthesized and evaluated with respect to their cytotoxicity and effects on cellular structures. As HNTs are water-insoluble, DNA is applied for wrapping the surface of HNTs to enhance their water-dispersibility. To investigate the potential of DNA-wrapped HNTs (HD) as a promising drug delivery carrier, doxorubicin (DOX) is introduced as a model anticancer agent and loaded onto HD. The DOX-loaded, DNA-wrapped HNTs (HDD) show sustained DOX release over two weeks without initial burst of DOX indicating delayed DOX release inside cells. In addition, effects of DNA-wrapped HNTs (HD) or HDD on the cytoskeleton organization of A549 cells are studied by visualizing the distribution of F-actin filaments using confocal laser scanning microscopy, and cellular morphological changes are observed by scanning electron microscopy and scanning ion conductance microscopy.

Polyaniline as a material for hydrogen storage applications.

The main challenge of commercialization of the hydrogen economy is the lack of convenient and safe hydrogen storage materials, which can adsorb and release a significant amount of hydrogen at ambient conditions. Finding and designing suitable cost-effective materials are vital requirements to overcome the drawbacks of investigated materials. Because of its outstanding electronic, thermal, and chemical properties, the electrically conducting polyaniline (PANI) has a high potential in hydrogen storage applications. In this review, the progress in the use of different structures of conducting PANI, its nanocomposites as well as activated porous materials based on PANI as hydrogen storage materials is presented and discussed. The effect of the unique electronic properties based on the π-electron system in the backbone of these materials in view of the hydrogen uptake and the relevant mechanisms are highlighted.

Polyaniline-polypyrrole composites with enhanced hydrogen storage capacities.

A facile method for the synthesis of polyaniline-polypyrrole composite materials with network morphology is developed based on polyaniline nanofibers covered by a thin layer of polypyrrole via vapor phase polymerization. The hydrogen storage capacity of the composites is evaluated at room temperature exhibits a twofold increase in hydrogen storage capacity. The HCl-doped polyaniline nanofibers exhibit a storage capacity of 0.46 wt%, whereas the polyaniline-polypyrrole composites could store 0.91 wt% of hydrogen gas. In addition, the effect of the dopant type, counteranion size, and the doping with palladium nanoparticles on the storage properties are also investigated.

Cellular interactions of a water-soluble supramolecular polymer complex of carbon nanotubes with human epithelial colorectal adenocarcinoma cells.

Water-soluble, PAX-loaded carbon nanotubes are fabricated by employing a synthetic polyampholyte, PDM. To investigate the suitability of the polyampholyte and the nanotubes as drug carriers, different cellular interactions such as the human epithelial Caco-2 cells viability, their effect on the cell growth, and the change in the transepithelial electrical resistance in Caco-2 cells are studied. The resulting complex is found to exhibit an effective anti-cancer effect against colon cancer cells and an increased the reduction of the electrical resistance in the Caco-2 cells when compared to the precursor PAX.

Carbon nanotubes in the liquid phase: addressing the issue of dispersion.

The inherent size and hollow geometry with extraordinary electronic and optical properties make carbon nanotubes (CNTs) promising building blocks for molecular or nanoscale devices. Unfortunately, their hydrophobic nature and their existence in the form of agglomerated and parallel bundles make this interesting material inadequately soluble or dispersible in most of the common solvents, which is crucial to their processing. Therefore, various ingenious techniques have been reported to disperse the CNTs in various solvents with different experimental conditions. However, by analyzing the published scientific research articles, it is evident that there is an important issue or misunderstanding between the term "dispersion" and "solubilization". As a result many researchers use the terms interchangeably, particularly when stating the interaction of CNTs with liquids, which causes confusion among the readers, students, and researchers. In this article, this fundamental issue is addressed in order to give basic insight to the researchers who are working with CNTs, as well as to the scientists who deal with nano-related research domains.

Cytotoxicity and cellular uptake of lysozyme-stabilized gold nanoparticles.

The particle size and surface properties of gold nanoparticles are critical factors for the interactions between nanoparticles and cells. To produce noncytotoxic gold nanoparticles, a straightforward method for the synthesis of gold nanoparticles designed involving the reduction and stabilization by a protein such as a lysozyme in conjunction with microwave irradiation. The cooperative combination of a lysozyme with a high affinity for metal ions and the microwave irradiation allowed to form biocompatible gold nanoparticles in an aqueous system. In addition, the cell toxicity and the cellular uptake pathways of the gold nanoparticles synthesized against mouse embryonic fibroblast NIH-3T3 cells were studied and found to be taken up by receptor-mediated endocytosis. In addition, the lysozyme-stabilized gold nanoparticles are accumulated in the cytoplasm as well as the nucleus without any significant cytotoxicity.

Shape-tailoring and catalytic function of anisotropic gold nanostructures.

We report a facile, one-pot, shape-selective synthesis of gold nanoparticles in high yield by the reaction of an aqueous potassium tetrachloroaurate(III) solution with a commercially available detergent. We prove that a commercial detergent can act as a reducing as well as stabilizing agent for the synthesis of differently shaped gold nanoparticles in an aqueous solution at an ambient condition. It is noteworthy that the gold nanoparticles with different shapes can be prepared by simply changing the reaction conditions. It is considered that a slow reduction of the gold ions along with shape-directed effects of the components of the detergent plays a vital function in the formation of the gold nanostructures. Further, the as-prepared gold nanoparticles showed the catalytic activity for the reduction reaction of 4-nitrophenol in the presence of sodium borohydride at room temperature.

Polyampholyte-Wrapped Carbon Nanotubes: Preparation and Internalization by Embryonic Fibroblast Cells.

The cytotoxicity and cellular uptake of carbon nanotubes (CNTs) has recently attracted considerable interest because of the issue of biosphere-nanomaterial interactions. The biocompatibility of CNTs is determined by the metal impurities in the CNTs, the size of the CNTs and the CNT dispersion states; in particular, the type of surface modifications on the CNTs affects how they interact with cells and determines their cytotoxicity and cellular uptake. In this study, biocompatible single-walled carbon nanotubes (SWNTs) wrapped with a water-soluble copolymer, poly[2-(dimethylamino)ethyl methacrylate-co-methacrylic acid] (PDM), were prepared. We report that these SWNTs have enhanced water dispersibility and cellular internalization but no significant cytotoxic activity against mouse embryonic fibroblast NIH-3T3 cells.

Carbon nanotubes: are they dispersed or dissolved in liquids?

Carbon nanotubes (CNTs) constitute a novel class of nanomaterials with remarkable applications in diverse domains. However, the main intrincsic problem of CNTs is their insolubility or very poor solubility in most of the common solvents. The basic key question here is: are carbon nanotubes dissolved or dispersed in liquids, specifically in water? When analyzing the scientific research articles published in various leading journals, we found that many researchers confused between "dispersion" and "solubilization" and use the terms interchangeably, particularly when stating the interaction of CNTs with liquids. In this article, we address this fundamental issue to give basic insight specifically to the researchers who are working with CNTs as well asgenerally to scientists who deal with nano-related research domains.

Shape-tailoring of gold nanostructures: can a detergent act as the reducing or protecting agent?

A commercially available detergent was found to be an effective reducing as well as stabilizing agent for the synthesis of differently shaped gold nanoparticles in an aqueous solution at an ambient condition and the as-prepared gold nanoparticles behave as an efficient catalyst for the reduction reaction of 4-nitrophenol at room temperature.

Cyclodextrin supramacromolecules: unexpected formation in aqueous phase under ambient conditions.

The unexpected formation of supramacromolecules of ß-cyclodextrin in aqueous solution under ambient conditions is reported in this article. The shape and size of the supramacromolecules could be controlled by varying the stirring time and the concentration. The supramolecular interactions of the supramacromolecules were confirmed by ¹H NMR spectroscopy. Additionally, visual evidence of the supramacromolecules was provided by transmission and scanning electron microscopy. The thermal behavior of the supramacromolecules was examined by thermogravimetric analysis. The molecular mass determination by gel permeation chromatography showed that the supramacromolecules had a high molar mass.

Cucurbit[7]uril as a tool in the green synthesis of gold nanoparticles.

A simple, green, one-pot synthesis of gold nanoparticles was achieved through the reaction of an aqueous mixture of potassium tetrachloroaurate(III) and the macrocycle cucurbit[7]uril in the presence of sodium hydroxide at room temperature without introducing any kind of traditional reducing agents and/or external energy. The as-prepared gold nanoparticles showed catalytic activity for the reduction reaction of 4-nitrophenol in the presence of NaBH(4), which has been established by visual inspection and UV/Vis spectroscopy. This report is the first for the preparation of gold nanoparticles using cucurbit[7]uril in aqueous media through chemical reduction without employing conventional reducing agents and/or external energy.