Electrospun glassy carbon ultra-thin layer chromatography devices

The development and application of electrospun glassy carbon nanofibers for ultra-thin layer chromatography (UTLC) are described. The carbon nanofiber stationary phase is created through the electrospinning and pyrolysis of SU-8 2100 photoresist. This results in glassy carbon nanofibers with diameters of ∼200–350 nm that form a mat structure with a thickness of ∼15 μm. The chromatographic properties of UTLC devices produced from pyrolyzed SU-8 heated to temperatures of 600, 800, and 1000 °C are described. Raman spectroscopy and scanning electron microscopy (SEM) are used to characterize the physical and molecular structure of the nanofibers at each temperature. A set of six laser dyes was examined to demonstrate the applicability of the devices. Analyses of the retention properties of the individual dyes as well as the separation of mixtures of three dyes were performed. A mixture of three FITC-labeled essential amino acids: lysine, threonine and phenylalanine, was examined and fully resolved on the carbon UTLC devices as well. The electrospun glassy carbon UTLC plates show tunable retention, have plate number, N, values above 10,000, and show physical and chemical robustness for a range of mobile phases.     

Aligned electrospun nanofibers for ultra-thin layer chromatography

The fabrication and implementation of aligned electrospun polyacrylonitrile (PAN) nanofibers as a stationary phase for ultra-thin layer chromatography (UTLC) is described. The aligned electrospun UTLC plates (AE-UTLC) were characterized to give an optimized electrospun mat consisting of high nanofiber alignment and a mat thickness of ∼25 μm. The AE-UTLC devices were used to separate a mixture of β-blockers and steroidal compounds to illustrate the properties of AE-UTLC. The AE-UTLC plates provided shorter analysis time (∼2–2.5 times faster) with improved reproducibility (as high as 2 times) as well as an improvement in efficiency (up to100 times greater) relative to non-aligned electrospun-UTLC (E-UTLC) devices.     

UTLC: An Advanced Technique in Planar Chromatography

As part of increasing research in the field of separation science, there have been many efforts to undertake planar chromatography with more efficient separation and better resolution in the shortest period of time, together with a specificity and a capability to identify more precisely an unknown compound present in a mixture. Ultra-thin layer chromatography (UTLC) is a modern technique which gives separation within 10–30 mm and development in just 1–6 min, with the consumption of less solvent. The stationary phase of UTLC is made up of a silica gel monolithic layer of 10 μm thickness having 3- to 4-nm mesopores and 1- to 2-μm macropores. Glancing angle deposition (GLAD)-UTLC is a modification of UTLC which gives separation within 15 mm distance and in less than 2 min. Anisotropic media of GLAD UTLC gives a unique migration direction effect. UTLC atmospheric pressure–matrix-assisted laser desorption ionizer–mass spectrometery (UTLC-AP-MALDI-MS) is a choice of technique for the identification of an unknown compound in a mixture or an impure form. ULTC-AP-MALDI-MS allows the fast changing of plates, produces more intact protonated molecules, less fragmentation and less entry of chromatographic material, and yielding less complicated spectra than the vacuum condition. Thus, UTLC is a useful technique for very rapidly giving the separation and identification of new components present in mixtures. This review provides a brief overview of UTLC, the stationary phases used for UTLC, and the detection options and applications of UTLC.     

Morphological modification of nanostructured ultrathin-layer chromatography stationary phases

Ultrathin-layer chromatography (UTLC) provides the high sensitivities and rapid separations over short distances desirable in many analytical applications. The dependence of these performance benefits on UTLC layer microstructure motivates continued stationary phase engineering efforts. A new method of modifying the elution behaviours of nanostructured thin film UTLC stationary phases is investigated in this report. Macroporous normal phase silica thin films ～5 μm thick were fabricated using glancing angle deposition (GLAD). Reactive ion etching (RIE) and a subsequent annealing treatment modified stationary phase morphology to tune migration velocity, analyte retention, and overall separation performance. Combining this technique with a RIE shadow mask enabled fabrication of adjacent concentration and separation zones with markedly different elution properties. Although produced using an entirely new approach, GLAD UTLC concentration zone media behaved in a manner consistent with traditional thin-layer chromatography (TLC) and high-performance TLC (HPTLC) concentration zone plates. In particular, these new media focused large volume, low concentration dye mixture spots into narrow bands to achieve high-quality separations. The described approach to modifying the morphology and resultant elution behaviours of nanostructured stationary phases expands the capabilities of the GLAD UTLC technique.     

Functionalized carbon nanotube/polyacrylonitrile composite nanofibers: fabrication and properties

The functionalized multi‐walled carbon nanotubes (f‐MWCNTs) were obtained by Friedel–Crafts acylation, which introduced aromatic amine groups onto the sidewall. And the grafted yield was adjusted by controlling the concentration of the catalyst. The composite solutions containing f‐MWCNTs and polyacrylonitrile (PAN) were then prepared by in‐situ or ex‐situ solution polymerization. The resulting solutions were electrospun into composite nanofibers. In the in‐situ polymerization, morphological observation revealed that f‐MWCNTs was uniformly dispersed along the axes of the nanofibers and increased interfacial adhesion between f‐MWCNTs and PAN. Furthermore, two kinds of f‐MWCNTs/PAN composite nanofibers had a higher degree of crystallization and a larger crystal size than PAN nanofibers had, so the specific tensile strengths and modulus of the composite nanofibers were enhanced. And the thermal stability of f‐MWCNTs/PAN from in‐situ method was higher than that of ex‐situ system. When the f‐MWCNTs content was less than 1 wt%, the specific tensile strengths and modulus of nanofibers were enhanced with increase in the amounts of f‐MWCNTs, and f‐MWCNTs/PAN of in‐situ system provided better mechanical properties than that of ex‐situ system. Copyright © 2010 John Wiley & Sons, Ltd.     

Improved cellular response on multiwalled carbon nanotube-incorporated electrospun polyvinyl alcohol/chitosan nanofibrous scaffolds

We report the fabrication of multiwalled carbon nanotube (MWCNT)-incorporated electrospun polyvinyl alcohol (PVA)/chitosan (CS) nanofibers with improved cellular response for potential tissue engineering applications. In this study, smooth and uniform PVA/CS and PVA/CS/MWCNTs nanofibers with water stability were formed by electrospinning, followed by crosslinking with glutaraldehyde vapor. The morphology, structure, and mechanical properties of the formed electrospun fibrous mats were characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, and mechanical testing, respectively. We showed that the incorporation of MWCNTs did not appreciably affect the morphology of the PVA/CS nanofibers; importantly the protein adsorption ability of the nanofibers was significantly improved. In vitro cell culture of mouse fibroblasts (L929) seeded onto the electrospun scaffolds showed that the incorporation of MWCNTs into the PVA/CS nanofibers significantly promoted cell proliferation. Results from this study hence suggest that MWCNT-incorporated PVA/CS nanofibrous scaffolds with small diameters (around 160 nm) and high porosity can mimic the natural extracellular matrix well, and potentially provide many possibilities for applications in the fields of tissue engineering and regenerative medicine.     

Graphene oxide improved thermal and mechanical properties of electrospun methyl stearate/polyacrylonitrile form-stable phase change composite nanofibers

In the present work, a novel PAN-based form-stable composite phase change materials with the methyl stearate (MES) encapsulated in the supporting matrices of polyacrylonitrile (PAN) nanofibers were fabricated through electrospunning for the storage and retrieval of thermal energy. Influences of graphene oxide (GO) addition on the chemical properties, structural morphologies, mechanical properties, thermal energy storage properties, thermal stability, and thermal energy storage/retrieval rates of electrospun MES/PAN/GO phase change composite nanofibers were systematically investigated by FT-IR, FE-SEM, tensile testing, DSC, TG, and measurement of melting/freezing times, respectively. The results revealed that the incorporation of GO effectively enhanced the mechanical properties, thermal stability, as well as heat storage and release rates of the phase change composite nanofibers. The averaged tensile strength of electrospun MES/PAN/GO phase change composite nanofibers increased significantly by 573 % with 10 mass% loading of GO, while elongation at break had a maximum 107 % increment when adding 3 mass% of GO. The DSC results indicated that the electrospun PAN-based phase change composite nanofibers with various GO loadings had suitable phase transition temperatures with the latent heat ranging from about 92 to 109 kJ kg^?1 and exhibited good thermal reliability in terms of DSC measurements during 50 melting-freezing cycles. Moreover, the melting and freezing time were significantly decreased about 44 and 43 % for the MES/PAN/GO5, as well as 59 and 64 % for the MES/PAN/GO10 after introducing the GO into the composite nanofibers systems.     

Ultrathin-layer chromatography

The development of ultrathin-layer silica gel plates with a monolithic structure opens up a new dimension in thin-layer chromatography (TLC). The very small layer thickness of approximately 10 microm and the absence of any kind of binder in combination with the framework of this stationary phase lead to new and improved properties of these ultrathin-layer chromatographic (UTLC) silica-gel plates compared with conventional TLC and high-performance TLC (HPTLC) precoated layers. First of all, the advantages of the UTLC plates are the very short migration distances and, in combination with this, the short development times as well as the very low consumption of solvents as the mobile phase in connection with high sensitivity. The separations of amino acids, pesticides, pharmaceutically active ingredients, phenols, and plasticizers effectively demonstrate the possibilities of the new ultrathin-layer silica-gel plates. Furthermore, a comparison of UTLC, HPTLC, and TLC concerning retention behavior, efficiency, detection limits, migration times, and solvent consumption is performed effectively by the separation of caffeine and paracetamol.     

Lignin bio-oil-based electrospun nanofibers with high substitution ratio property for potential carbon nanofibers applications

We reported a new approach for development of lignin bio-oil-based electrospun nanofibers (LENFs) that had high substitution ratio (up to 80 wt%) and good morphology. This approach was particularly unique and translatable as it used small molecule lignin bio-oil with high reactivity and low heterogeneity obtained via lignin depolymerization reaction to produce well-oriented LENFs. Firstly, effects of various blends solutions ratios and electrospinning parameters on the characteristics of the obtained LENFs were analyzed. The results showed that the optimal parameters that resulted in the best electrospun nanofibers were as follows: blend solution ratio, the 20 wt% blend solution containing 80 wt% straw lignin bio-oil (SLB) and 20 wt% polyacrylonitrile (PAN), flow rate, 1 mL/h, voltage, 20 kV, rotational speed, 500 r/min and the distance between needle and collection screen, 20 cm. Secondly, used the best LENFs, we also applied to prepare lignin bio-oil-based carbon nanofibers (LCNFs) and estimated its properties by scanning electron microscope (SEM), X-ray diffraction (XRD) patterns, Raman spectroscopy and tension testing. Our results demonstrated that compared with pure PAN carbon nanofibers (PCNFs), the as-prepared LCNFs had similar smooth surfaces, similar crystallinity and similar mechanical properties. This work can promote the utilization of lignin depolymerization main-products to produce lignin-based materials, while also help to reduce use of high-cost PAN.     

Thermal energy storage and retrieval properties of form-stable phase change nanofibrous mats based on ternary fatty acid eutectics/polyacrylonitrile composite by magnetron sputtering of silver

This paper demonstrated a novel magnetron sputtering method used for the improvement in thermal energy storage and retrieval rates of phase change materials (PCMs). The ten types of ternary fatty acid eutectics (i.e., CA–LA–MA, CA–LA–PA, CA–LA–SA, CA–MA–PA, CA–MA–SA, CA–PA–SA, LA–MA–PA, LA–MA–SA, LA–PA–SA and MA–PA–SA) were firstly prepared using five fatty acids such as capric acid (CA), lauric acid (LA), myristic acid (MA), palmitic acid (PA) and stearic acid (SA) and then selected as solid–liquid PCMs. Thereafter, magnetron sputter coating was used to deposit the functional silver (Ag) nanolayers onto the surface of electrospun polyacrylonitrile (PAN) nanofibrous mats serving as supporting skeleton. Finally, a series of composite PCMs were fabricated by adsorbing the prepared ternary eutectics into three-dimensional porous network structures of Ag-coated PAN membranes. The observations by EDX determined the formation of Ag nanolayers on the PAN nanofibers surface after magnetron sputtering. The SEM images illustrated that the Ag-coated PAN nanofibers appeared to have larger fiber diameter and rougher surface. Ag-coated PAN nanofibrous mats could effectively prevent the leakage of molten ternary eutectics and help maintain form-stable structure due to surface tension forces, capillary and nanoconfinement effects. The DSC results suggested that the phase change temperatures of the ternary fatty acid eutectics were obviously lower than those of individual fatty acids and their binary eutectics. The adsorption rates of ternary fatty acid eutectics in the composite PCMs were determined to be about 89–98 %. The thermal performance test indicated that the metallic coating of Ag dramatically improved the thermal energy storage and retrieval rates of the composite PCMs.     

Aggregation states of rhodamine 6G in electrospun nanofibrous films

Novel fluorescent composite nanofibrous films of rhodamine 6G (Rh6G) and polyacrylonitrile (PAN) are first prepared by electrospinning. The aggregation states of Rh6G in electruspun nanofibrous films are studied as a function of concentrations and characterized by UV–vis absorption spectroscopy and emission and excitation fluorescence spectroscopy. We have also used casting films as reference material to compare the effect of incorporation of Rh6G in electrospun nanofibrous films and casting films. The large specific surface area of the nanofibers and fast evaporation of the solvents in the electrospinning process reduced the aggregation of Rh6G. The appearance of fluorescent J-type dimers, even at higher dye concentration in elctrospun films, demonstrates that the electrospun films are an ideal material for incorporation of fluorescent dyes.     

Ultrathin-Layer Chromatography (UTLC)

Ultrathin-layer chromatography (UTLC) differs from high-performance thin-layer chromatography (HPTLC) and from thin-layer chromatography (TLC) in two basis things: the layer thickness, and the migration distances of the analytes. UTLC has a monolithic or a nanostructured stationary silica gel phase bound directly to the glass plates. Layer thickness in UTLC is 10 μm, instead of 100–250 μm in HPTLC. Migration distances are in the range of 1–3 cm for UTLC, instead of 8–10 cm for HPTLC. Therefore, the major advantages of UTLC over HPTLC and TLC are the shorter development times and higher separation efficiency and sensitivity. Moreover, separations on UTLC plates require smaller reagent and sample volumes. However, the UTLC plates are very difficult to manage with the TLC and HPTLC equipment currently available. Therefore, the next challenge in this area is the development of an inexpensive solution with appropriate instrumentation (sensitive optical scanners and sample application systems). UTLC had been used for separations of many compounds, e.g., pharmaceutically active ingredients, pesticides, plasticisers, natural products, and other chemical substances.     

Fabrication of well‐aligned electrospun nanofibrous membrane based on fluorinated polyimide

We have fabricated novel nanofibrous fluorinated polyimide membranes on a specially designed collector, which is composed of conductive aluminum plates and glass insulator materials and can be removed from the apparatus, using an electrospinning method. We describe the structure and water flux properties of the nanofibrous fluorinated polyimide membranes. The electrospun nanofibers were deposited across the plates and uniaxially aligned to the collector. In addition, the multi‐layer stacked nanofibrous membranes, consisting of three‐dimensionally ordered nanopores, were produced. The pure water fluxes for the stacked membranes were measured, using a stirred dead‐end filtration cell, and were linearly decreased with an increasing deposition time, indicating that the nanopores formed in the nanofibrous membrane were further narrowed due to the regularly accumulated nanofibers. Copyright © 2009 John Wiley & Sons, Ltd.     

In-Vitro Cytotoxicity Study: Cell Viability and Cell Morphology of Carbon Nanofibrous Scaffold/Hydroxyapatite Nanocomposites

Electrospun carbon nanofibers (CNFs), which were modified with hydroxyapatite, were fabricated to be used as a substrate for bone cell proliferation. The CNFs were derived from electrospun polyacrylonitrile (PAN) nanofibers after two steps of heat treatment: stabilization and carbonization. Carbon nanofibrous (CNF)/hydroxyapatite (HA) nanocomposites were prepared by two different methods; one of them being modification during electrospinning (CNF-8HA) and the second method being hydrothermal modification after carbonization (CNF-8HA; hydrothermally) to be used as a platform for bone tissue engineering. The biological investigations were performed using in-vitro cell counting, WST cell viability and cell morphology after three and seven days. L929 mouse fibroblasts were found to be more viable on the hydrothermally-modified CNF scaffolds than on the unmodified CNF scaffolds. The biological characterizations of the synthesized CNF/HA nanofibrous composites indicated higher capability of bone regeneration.     

Fabrication of nanocomposite PAN nanofibers containing MgO and Al2O3 nanoparticles

This paper describes the effect of embedding MgO and Al₂O₃ nanoparticles on the diameter of electrospun composite polyacrylonitrile (PAN) nanofibers. Diameter of nanofibers determines the important properties of the nanofibrous mats used in a variety of developed applications such as tissue engineering scaffolds, drug delivery, catalysis, ultra filtration, sensors, and nanoelectronics. The results showed that the type and amount of nanoparticles dispersed in PAN solutions affect the conductivity as well as the viscosity of the electrospinning solutions. Increasing the amount of MgO and Al₂O₃ leads to higher conductivity and higher viscosity of the electrospinning solution and ultimately to a smaller nanofiber diameter. Moreover, the results showed that higher conductivity of the electrospinning solution overcomes the effect of higher viscosity. Finally, no interaction was detected between metal oxide nanoparticles and PAN macromolecules.     

Acetylcholinesterase Immobilization on Polyacrylamide/Functionalized Multi-walled Carbon Nanotube Nanocomposite Nanofibrous Membrane

In this work, polyacrylamide/multi-walled carbon nanotubes (MWCNT) solution is electrospun to nanocomposite nanofibrous membranes for acetylcholinesterase enzyme immobilization. A new method for enzyme immobilization is proposed, and the results of analysis show successful covalent bonding of enzymes on electrospun membrane surface besides their non-covalent entrapment. Fourier transform infrared spectroscopy, mechanical and thermal investigations of nanofibrous membrane approve successful cross-linking and enzyme immobilization. The enzyme relative activity and kinetic on both pure and nanocomposite membranes is investigated, and the results show proper performance of designed membrane to even improve the enzyme activity followed by immobilization compared to free enzyme. Scanning electron microscopy images show nanofibrous web of 3D structure with a low shrinkage and hydrogel structure followed by enzyme immobilization and cross-linking. Moreover, the important role of functionalized carbon nanotubes on final nanofibrous membrane functionality as a media for enzyme immobilization is investigated. The results show that MWCNT could act effectively for enzyme immobilization improvement via both physical (enhanced fibers’ morphology and conductivity) and chemical (enzyme entrapment) methods.

Controlled release of doxorubicin from electrospun MWCNTs/PLGA hybrid nanofibers

In this study, multiwalled carbon nanotubes (MWCNTs) were used to encapsulate a model anticancer drug, doxorubicin (Dox). Then, the drug-loaded MWCNTs (Dox/MWCNTs) with an optimized drug encapsulation percentage were mixed with poly(lactide-co-glycolide) (PLGA) polymer solution for subsequent electrospinning to form drug-loaded composite nanofibrous mats. The structure, morphology, and mechanical properties of the formed electrospun Dox/PLGA, MWCNTs/PLGA, and Dox/MWCNTs/PLGA composite nanofibrous mats were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, and tensile testing. In vitro viability assay and SEM morphology observation of mouse fibroblast cells cultured onto the MWCNTs/PLGA fibrous scaffolds demonstrate that the developed MWCNTs/PLGA composite nanofibers are cytocompatible. The incorporation of Dox-loaded MWCNTs within the PLGA nanofibers is able to improve the mechanical durability and maintain the three-dimensional structure of the nanofibrous mats. More importantly, our results indicate that this double-container drug delivery system (both PLGA polymer and MWCNTs are drug carriers) is beneficial to avoid the burst release of the drug and able to release the antitumor drug Dox in a sustained manner for 42 days. The developed composite electrospun nanofibrous drug delivery system may be used as therapeutic scaffold materials for post-operative local chemotherapy.     

A novel two-nozzle electrospinning process for preparing microfiber reinforced pH-sensitive nano-membrane with enhanced mechanical property

A novel pH sensitive membrane (pHS-M) with mechanical integrity is synthesized firstly by two nozzles electrospining in this work. We report an excellent strategy here to combine indicative nanofiber from 9% PAN solution and micro-sized fibers from 20% PA-66 solution homogeneously in one electrospinning setup. The pH indicative property of electrospun sheet can be achieved by PAN nanofibers that first aminating with ethylenediamine and then immobilizing phenolphthalein covalently through a Mannich reaction, while micro-sized PA-66 fibers are responsible for the improvement of mechanical property of electrospun mat due to their elastic and flexible behavior. The composite membrane was characterized by SEM, FTIR and UV–vis spectroscopy. Results show that two kinds of pH sensitive membranes (single PAN nanofibers (pHS-NF) or composite PAN/PA-66 fiber (pHS-CF)) all exhibited remarkable color change from pale yellow to violet in a wide range of alkaline solution and rapid response time within 100 s. But after added of microfiber, the tensile strength was enhanced from 1.3 MPa to 6.90 MPa prominently which is beneficial to put the membrane into practice.     

Preparation of porous ultrafine polyacrylonitrile (PAN) fibers by electrospinning

A facile method for the preparation of porous ultrafine nanofibers was demonstrated. The PAN/NaHCO₃ composite nanofibers were electrospun, and then NaHCO₃ was removed by a selective dissolution and reaction with the solution of hydrochloric acid (10 wt%). The obtained PAN fibers showed highly porous surfaces after the extraction of NaHCO₃. The structure and properties of ultrafine PAN nanofibers were characterized by Fourier transform infrared (FT‐IR), X‐ray diffraction (XRD), and thermogravimetry (TG). The results indicated that NaHCO₃ could be introduced into the PAN solution and successfully electrospun. CO₂ is released and pores are formed on the fibers. The morphology image of the fibers was detected by scanning electron microscope (SEM) and showed that many pores aligned the nanofibers. Copyright © 2008 John Wiley & Sons, Ltd.     

Incorporation of ionic liquid into porous polymer monoliths to enhance the separation of small molecules in reversed‐phase high‐performance liquid chromatography

An ionic liquid was incorporated into the porous polymer monoliths to afford stationary phases with enhanced chromatographic performance for small molecules in reversed‐phase high‐performance liquid chromatography. The effect of the ionic liquid in the polymerization mixture on the performance of the monoliths was studied in detail. While monoliths without ionic liquid exhibited poor resolution and low efficiency, the addition of ionic liquid to the polymerization mixture provides highly increased resolution and high efficiency. The chromatographic performances of the monoliths were demonstrated by the separations of various small molecules including aromatic hydrocarbons, isomers, and homologues using a binary polar mobile phase. The present column efficiency reached 27 000 plates/m, which showed that the ionic liquid monoliths are alternative stationary phases in the separation of small molecules by high‐performance liquid chromatography