A mesoporous silica nanosphere-based carrier system with chemically removable CdS nanoparticle caps for stimuli-responsive controlled release of neurotransmitters and drug molecules

An MCM-41 type mesoporous silica nanosphere-based (MSN) controlled-release delivery system has been synthesized and characterized using surface-derivatized cadmium sulfide (CdS) nanocrystals as chemically removable caps to encapsulate several pharmaceutical drug molecules and neurotransmitters inside the organically functionalized MSN mesoporous framework. We studied the stimuli-responsive release profiles of vancomycin- and adenosine triphosphate (ATP)-loaded MSN delivery systems by using disulfide bond-reducing molecules, such as dithiothreitol (DTT) and mercaptoethanol (ME), as release triggers. The biocompatibility and delivery efficiency of the MSN system with neuroglial cells (astrocytes) in vitro were demonstrated. In contrast to many current delivery systems, the molecules of interest were encapsulated inside the porous framework of the MSN not by adsorption or sol-gel types of entrapment but by capping the openings of the mesoporous channels with size-defined CdS nanoparticles to physically block the drugs/neurotransmitters of certain sizes from leaching out. We envision that this new MSN system could play a significant role in developing new generations of site-selective, controlled-release delivery nanodevices.     

Heterostructured magnetic nanotubes

Heterostructured magnetic tubes with submicrometer dimensions were assembled by the layer-by-layer deposition of polyelectrolytes and nanoparticles in the pores of track-etched polycarbonate membranes. Multilayers composed of poly(allylamine hydrochloride) and poly(styrene sulfonate) assembled at high pH (pH > 9.0) were first assembled into the pores of track-etched polycarbonate membranes, and then multilayers of magnetite (Fe3O4) nanoparticles and PAH were deposited. Transmission electron microscopy (TEM) confirmed the formation of multilayer nanotubes with an inner shell of magnetite nanoparticles. These tubes exhibited superparamagnetic characteristics at room temperature (300 K) as determined by a SQUID magnetometer. The surface of the magnetic nanotubes could be further functionalized by adsorbing poly(ethylene oxide)-b-poly(methacrylic acid) block copolymers. The separation and release behavior of low molecular weight anionic molecules (i.e., ibuprofen, rose bengal, and acid red 8) by/from the multilayer nanotubes were studied because these tubes could potentially be used as separation or targeted delivery vehicles. The magnetic tubes could be successfully used to separate (or remove) a high concentration of dye molecules (i.e., rose bengal) from solution by activating the nanotubes in acidic solution. The release of the anionic molecules in physiologically relevant buffer solution showed that whereas bulky molecules (e.g., rose bengal) release slowly, small molecules (i.e., ibuprofen) release rapidly from the multilayers. The combination of the template method and layer-by-layer deposition of polyelectrolytes and nanoparticles provides a versatile means to create functional nanotubes with heterostructures that can be used for separation as well as targeted delivery.     

Microchips as Controlled Drug-Delivery Devices

Controlled-release systems are common in a number of product areas, including foods, cosmetics, pesticides, and paper. Microencapsulated systems, for example, are used for the release of flavors and vitamins in foods, fragrances in perfumes, and inks in carbonless copy paper. Controlled-release systems for drug delivery first appeared in the 1960s and 1970s. In the past three decades, the number and variety of controlled release systems for drug-delivery applications has increased dramatically. Many of these use polymers having particular physical or chemical characteristics such as biodegradability, biocompatibility, or responsiveness to pH or temperature changes. However, recent advances in the field of microfabrication have created the possibility of a new class of controlled-release systems for drug delivery, namely, that of small, programmable devices. Their small size, potential for integration with microelectronics, and ability to store and release chemicals on demand could make controlled-release microchips useful in a number of areas, including medical diagnostics, analytical chemistry, chemical detection, industrial process monitoring and control, combinatorial chemistry, microbiology, and fragrance delivery. More importantly, drug-delivery microchips resulting from this convergence of controlled release and microfabrication technologies may provide new treatment options to clinicians in their fight against disease.     

Achieving Direct Electrical Connection to Glucose Oxidase Using Aligned Single Walled Carbon Nanotube Arrays

Direct electron transfer between an electrode and the redox active centre of glucose oxidase, flavin adenine dinucleotide (FAD), is probed using carbon nanotube modified gold electrodes. Gold electrodes are first modified with a self‐assembled monolayer of cysteamine and then shortened single walled carbon nanotubes (SWNT) are aligned normal to the electrode surface by self‐assembly. The electrochemistry of these aligned nanotube electrode arrays is initially investigated using potassium ferricyanide which showed SWNT act as nanoelectrodes with the ends of the tubes more electrochemically active than the walls. Subsequently the nanotubes are plugged into the enzymes in one of two ways. In the first method, native glucose oxidase is covalently attached to the ends of the aligned tubes which allowed close approach to FAD and direct electron transfer to be observed with a rate constant of 0.3 s^?1. In the second strategy, FAD was attached to the ends of the tubes and the enzyme reconstituted around the surface immobilized FAD. This latter approach allowed more efficient electron transfer to the FAD with a rate constant of 9 s^?1.     

Dissociation of electrolytes in a nano-aqueous system within single-wall carbon nanotubes

Research on material incorporation within single-wall carbon nanotubes (SWNTs) through aqueous solutions of various electrolytes is performed for the purpose of providing a foundation for future application of SWNTs to, for example, drug delivery systems. We have determined that the optical spectra of SWNTs were significantly affected when SWNTs that had opened holes or removed caps were treated through immersion in an aqueous solution of electrolytes, followed by drying at room temperature; however, the spectra of SWNTs without opened holes or removed caps were not subjected to such treatment. We infer that when the sucked solutions remained inside the tubes, even after drying (the nano-aqueous system), the electrolyte was dissociated into ions, which was likely to change the electronic states of SWNTs. On the other hand, when the SWNTs were well-dried under vacuum, no remarkable changes in their optical spectra were observed.     

Shaping Carbon Nanotubes with Chemistry

As-grown, string-shaped single-walled carbon nanotubes were transformed into other shapes by applications of organic chemistry. Cutting carbon nanotubes in strong acids affords oxygen-containing groups at both ends of the open tubes. These groups were utilized for ring-closure reactions in very dilute conditions. Atomic force microscopy reveals ring-shaped nanotubes with a mean diameter of 540 nm as products. Also, the end groups were used to react with the surface amine groups of PAMAM dendrimer. It gave star-shaped structures in which straight nanotubes are radiating from dendrimer centers. These experiments clearly demonstrate that covalent chemistry is useful for construction of super-structured carbon nanotubes.     

A glucose-responsive controlled release system using glucose oxidase-gated mesoporous silica nanocontainers

A glucose-responsive controlled-release system based on the competitive combination between glucose oxidase, glucosamine and glucose has been described, which exhibits perfect controlled release properties and high selectivity for glucose over other monosaccharides. This paved the way for a new generation of stimuli-responsive delivery systems.     

Kinetics of water filling the hydrophobic channels of narrow carbon nanotubes studied by molecular dynamics simulations

The kinetics of water filling narrow single-walled carbon nanotubes was studied using molecular dynamics simulations. The time required to fully fill a nanotube was linear with respect to the tube length. We observed that water molecules could enter into nanotubes of different lengths, either from one end or from both ends. The probability of having a nanotube filled completely from both ends increased exponentially with the tube length. For short tubes, filling usually proceeded from only one end. For long tubes, filling generally proceeded from both tube ends over three stages, i.e., filling from one end, filling from both ends, and filling from both ends with the dipole reorientation of water molecules to give a concerted ordering within the fully filled tube. The water molecules in the partially filled nanotube were hydrogen bonded similarly to those in the fully filled nanotube. Simulations for the reference Lennard-Jones fluid without hydrogen bonds were also performed and showed that the filling behavior of water molecules can be attributed to strong intermolecular hydrogen bonding.     

Optimum conditions for adsorptive storage

The storage of gases in porous adsorbents, such as activated carbon and carbon nanotubes, is examined here thermodynamically from a systems viewpoint, considering the entire adsorption-desorption cycle. The results provide concrete objective criteria to guide the search for the "Holy Grail" adsorbent, for which the adsorptive delivery is maximized. It is shown that, for ambient temperature storage of hydrogen and delivery between 30 and 1.5 bar pressure, for the optimum adsorbent the adsorption enthalpy change is 15.1 kJ/mol. For carbons, for which the average enthalpy change is typically 5.8 kJ/mol, an optimum operating temperature of about 115 K is predicted. For methane, an optimum enthalpy change of 18.8 kJ/mol is found, with the optimum temperature for carbons being 254 K. It is also demonstrated that for maximum delivery of the gas the optimum adsorbent must be homogeneous, and that introduction of heterogeneity, such as by ball milling, irradiation, and other means, can only provide small increases in physisorption-related delivery for hydrogen. For methane, heterogeneity is always detrimental, at any value of average adsorption enthalpy change. These results are confirmed with the help of experimental data from the literature, as well as extensive Monte Carlo simulations conducted here using slit pore models of activated carbons as well as atomistic models of carbon nanotubes. The simulations also demonstrate that carbon nanotubes offer little or no advantage over activated carbons in terms of enhanced delivery, when used as storage media for either hydrogen or methane.     

Clay nanotube encapsulation for functional biocomposites

Natural halloysite clay nanotubes with 50 nm outer- and 15 nm inner- diameters are described as miniature vehicles for sustained release of drugs and proteins. The release time may be adjusted from 10 to 200 h with the tube surface polymeric coating. An explanation of sustained release through locking electrical potential at the nanotube ends is suggested. These biocompatible ceramic tubes may be also used for architectural construction of nanoshells on microbes through alternation with polycations to enhance the intrinsic properties of biological cells. Halloysite nanotubes (pristine or drug-loaded) are well mixable with polar and low-polar polymers allowing for functional biocomposites with enhanced mechanical strength, adhesivity and slow release of drugs or other chemical agents. Halloysite is nontoxic abundantly available from natural deposit material which does not require exfoliation or other complicated energy consuming processing.     

气凝胶催化剂上甲烷裂解制备的碳纳米管结构特征

采用XRD、TGA、SEM、TEM、 Raman光谱等多种表征手段,考察了Al2O3气凝胶催化剂上甲烷裂解生长的碳纳米管的结构特征.制得的碳纳米管形态单一,为管径均匀、管壁光滑的中空纳米管,平均直径在10～20 nm.碳纳米管的比表面积较大,具有较强的抗氧化能力,其结构的长程有序度较石墨低.由碳纳米管的Raman光谱分析可知,碳纳米管存在碳层缺陷和无定形碳.当反应温度升高或甲烷浓度下降时,碳纳米管石墨化程度逐渐提高.     

Synthesis of pH-responsive mesoporous silica nanotubes for controlled release

A novel mesoporous silica tubes (MMT) which possessed pH-sensitive controlled release ability had been fabricated and synthesized by using carbon nanotubes (CNTs) as template. The sample replicated the morphologies of the CNTs successfully. The Brunauer–Emmett–Teller surface area of the materials can reach 1,017 m² g^?1 with the pore size of 3.8 nm. As a model drug, metformin HCl was applied to study the drug loading and control release ability of the materials. MMT possesses higher drug loading ratio (36 %) than that of MCM-41 (27.5 %). The release kinetics were studied in simulated gastric fluid (pH = 1.2) and in simulated proximal intestine fluid (pH = 7. 4), respectively. The result shows that the delivery systems exhibit well pH-sensitive control release ability and the as-synthesized materials have potential application in biomedical field.     

Mannose-Modified Multi-Walled Carbon Nanotubes as a Delivery Nanovector Optimizing the Antigen Presentation of Dendritic Cells

Dendritic cells (DCs) based cancer immunotherapy is largely dependent on adequate antigen delivery and efficient induction of DCs maturation to produce sufficient antigen presentation and ultimately lead to substantial activation of tumor-specific CD8⁺ T cells. Carbon nanotubes (CNTs) have attracted great attention in biomedicine because of their unique physicochemical properties. In order to effectively deliver tumor antigens to DCs and trigger a strong anti-tumor immune response, herein, a specific DCs target delivery system was assembled by using multi-walled carbon nanotubes modified with mannose which can specifically bind to the mannose receptor on DCs membrane. Ovalbumin (OVA) as a model antigen, could be adsorbed on the surface of mannose modified multi-walled carbon nanotubes (Man-MWCNTs) with a large drug loading content. This nanotube-antigen complex showed low cytotoxicity to DCs and was efficiently engulfed by DCs to induce DCs maturation and cytokine release in vitro, indicating that it could be a potent antigen-adjuvant nanovector of efficient antigen delivery for therapeutic purpose.     

Self-assembly of modified carbon nanotubes in toluene

The dispersibility of modified carbon nanotubes in toluene at different temperature has been investigated by laser light scattering. It was found that the nanotubes cannot be dispersed into the level of single tubes. On the other hand, the carbon nanotubes self-assemble in a crystal-like way, with a periodicity around 2 μm.     

Aromaticity of carbon nanotubes

Carbon nanotubes are composed of cylindrical graphite sheets. Both nanotubes and graphite sheets are benzenoid derivatives composed of sp2 carbon atoms arranged in a hexagonal pattern. Therefore both systems are aromatic. The extent of the aromatic character of a molecule G (here benzenoids) can be explained in terms of the number of possible Kekulé structures in G. In this work the Kekulé structures in carbon nanotubes and the corresponding, rectangular, graphite-sheets the tubes might originate from, were enumerated. It was shown that (2,2), (3,3), and (4,4) carbon nanotubes are more aromatic than the corresponding, rectangular, planar structures. This explains why it might be more difficult to saturate nanotubes by addition reactions than the respective, "narrow", graphite sheets.     

Enhanced adsorption of paracetamol on closed carbon nanotubes by formation of nanoaggregates: carbon nanotubes as potential materials in hot-melt drug deposition-experiment and simulation

We present the new results of systematic studies of paracetamol adsorption on closed, commercially available, unmodified carbon nanotubes. The results of thermal analysis, static adsorption measurements and the comparison with phenol adsorption data lead to suggestion that the formation of paracetamol nanoaggregates in the interstitial spaces between nanotubes occurs. This effect is also confirmed by the results of (performed in two ways) independent dynamic measurements and by molecular dynamics simulation technique. Next, we show that the behavior of adsorbed paracetamol during heating leads to the creation of a new drug delivery system. The properties of this system depend on the type of applied nanotubes and the parameters of the process called hot-melt drug deposition. Thus, we conclude that confined nanoaggregate formation, as well as hot-melt deposition should be promising effects in the preparation of highly effective, new drug delivery systems.     

Functionalizing Single-Wall Carbon Nanotubes in Hollow Cathode Glow Discharges

A hollow cathode glow discharge was used to functionalize single-wall carbon nanotubes. This low temperature, solvent free, facile and fast process may be used to efficiently attach various functional groups (COOH, OH, CH, NH₂, NO₂ and NO) to the open ends and sidewalls of carbon nanotubes. The presented technique yields a broader set of functional groups being attached to the tubes as compared to other discharge routes. A rich functionalized surface provides an attractive scaffold for the further coupling of complex molecules, e.g., enzymes, antibodies. In situ optical emission spectroscopy investigations provided detailed information of the dynamic processes within the plasma itself. The findings show a gas temperature of 480 K and suggest the functionalization occurs through radical addition channels that are assisted by N₂ ⁺ radical ion collisions viz. N₂ ⁺ ion radical bombardment breaks C–C bonds on SWNTs surface opening a path for subsequent addition and quenching for other radical species.     

A Biomimetic Escape Strategy for Cytoplasm Invasion by Synthetic Particles

The translocation of nanomaterials or complex delivery systems into the cytosol is a major challenge in nanobiotechnology. After receptor‐mediated endocytosis, most nanomaterials are sequestered and undergo degradation, therapy inactivation, or exocytosis. Herein we explore a novel surface particle coating made of adsorbed carbon nanotubes that provides coated materials with new properties that reproduce the viral cell‐invasive mechanisms, namely, receptor‐mediated endocytosis, endolysosomal escape, and cytosolic particle release preserving cell viability. This novel biomimetic coating design will enable the intracytoplasmic delivery of many different functional materials endowed with therapeutic, magnetic, optical, or catalytic functionalities, thus opening the door to a wide array of chemical and physical processes within the cytosolic or nuclear domains, and supporting new developments in the biotechnological, pharmaceutical, and biomedical industries.     

以吡啶为原料制备氮掺杂碳纳米管

在700～800 ℃,以吡啶为原料用CVD方法制备出了管径在20～40 nm的竹节状碳纳米管. EDX和XPS结果都表明氮掺杂到碳纳米管中. HRTEM研究发现掺氮碳纳米管的竹节由数层石墨片弯曲而成,纳米管外层石墨层逐渐消失.从Raman谱图的对照中发现,与相似条件下制备出的纯碳纳米管相比,氮掺杂碳纳米管的D谱带对G谱带的相对强度增加, TGA研究发现掺杂纳米管在较低温度下即被氧化,这些结果都说明氮掺杂使得纳米管的缺陷增加.     

Anion–π Catalysis on Carbon Nanotubes

Induced π acidity from polarizability is emerging as the most effective way to stabilize anionic transition states on aromatic π surfaces, that is, anion–π catalysis. To access extreme polarizability, we propose a shift from homogeneous toward heterogeneous anion–π catalysis on higher carbon allotropes. According to benchmark enolate addition chemistry, multi‐walled carbon nanotubes equipped with tertiary amine bases outperform single‐walled carbon nanotubes. This is consistent with the polarizability of the former not only along but also between the tubes. Inactivation by π‐basic aromatics and saturation with increasing catalyst concentration support that catalysis occurs on the π surface of the tubes. Increasing rate and selectivity of existing anion–π catalysts on the surface of unmodified nanotubes is consistent with transition‐state stabilization by electron sharing into the tubes, i.e., induced anion–π interactions. On pristine tubes, anion–π catalysis is realized by non‐covalent interfacing with π‐basic pyrenes.