Single Nanofiber Research Articles

Preparation and characterization of ß-lactoglobulin/poly(ethylene oxide) magnetic nanofibers for biomedical applications

Developing a single nanofiber containing magnetic nanoparticles (MGNPs) and whey proteins provides a preferable requirement to utilize the benefits of various amino acids and magnetization characteristics in a single nanostructure. In this study, ß-lactoglobulin (BLG), one of the major components of the aqueous whey protein isolate, and magnetic glass ceramic nanoparticles (MGNPs) colloid were formulated into nanofibrous morphology by electrospinning using the assist of a poly(ethylene oxide) (PEO). First, BLG:PEO with a ratio of 3:1 produced nanofibers with an average fiber diameter of 370 nm. To produce magnetized nanofiber scaffolds, the magnetic glass ceramic nanoparticles were added to the BLG-PEO solution with a ratio of 1, 3 and 7 wt%. The influence of the inorganic nanoparticles on the nanofibrous morphology of the electrospun scaffold was investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The nanofiber diameter decreased with increasing the nanoparticles concentration as the observed average diameters were 245, 163 and 152 nm for the scaffolds containing 1, 3 and 7 wt.% MGNPs, respectively. The chemical composition and the magnetic properties were characterized using FTIR, DSC and VSM analysis techniques. It was concluded that addition of MGNPs did not affect the chemical composition of the protein or the polymer. Accordingly, a cell proliferation assay confirmed that the magnetic nanofibers have no adverse effect on the human mesenchymal stem cell (hMSC) proliferation. These results confirm the possibility of using electrospun magnetic nanofibers for biomedical applications.

Simultaneous controlled release of 5-FU, DOX and PTX from chitosan/PLA/5-FU/g-C3N4-DOX/g-C3N4-PTX triaxial nanofibers for breast cancer treatment in vitro

In the present study, the tri-layer nanofibers were synthesized via triaxial electrospinning process to control the sustained delivery of Doxorubicin (DOX), Paclitaxel (PTX) and 5- fluorouracil (5-FU) anticancer drugs from nanofibers. The 5-FU molecules were incorporated into the core solution (chitosan/polyvinyl alcohol (CS/PVA)) to fabricate the CS/PVA/5-FU inner layer of nanofibers. The intermediate layer was prepared from poly(lactic acid)/chitosan (PLA/CS) nanofibers. The DOX and PTX molecules were initially loaded into the g-C3N4 nanosheets and following were incorporated into the PLA/CS solution to fabricate the outer layer of nanofibers. The synthesized nanosheets and nanofibers were characterized using XRD, SEM, TEM and UV–vis analysis. The PLA/PVA/CS/FU/g-C3N4/DOX/PTX single layer nanofibers were also synthesized via electrospinning method. The drug loading efficiency, degradation rate and anticancer drugs release profiles from single layer and tri-layer nanofibers were investigated under various intermediate and shell layer thicknesses. The pharmacokinetic studies were performed to understand the drugs release mechanism from nanofibers. The cell viability and cell attachment of drug loaded single layer and tri-layer nanofibers toward the MCF-7 breast cancer cells were examined to achieve an optimum nanofibrous formulation for the breast cancer treatment. The obtained results revealed the high activity of tri-layer nanofibers for the breast cancer cells killing.

A comparison of the performance of voltammetric aptasensors for glycated haemoglobin on different carbon nanomaterials-modified screen printed electrodes

The integration of carbon nanomaterials into electrochemical aptasensors has gained significant interest in the recent years because of their high electrical conductivity, mechanical strength, and large surface area. However, no comparative study has been reported so far between different carbon nanomaterials for aptasensing applications. Here, we report, a comparative investigation of six carbon electrode materials (carbon, graphene (G), graphene oxide (GO), multi-wall carbon nanotube (MWCNT), single walled carbon nanotube (SWCNT) and carbon nanofiber (CNF)) on the performance of glycated haemoglobin (HbA1c) aptasensor prepared by physical adsorption. The aptamers were non-covalently immobilized on the six nanomaterial electrodes via π-π stacking interactions between the DNA nucleobases and the surface of the carbon material which creates a barrier to the electron transfer. However, upon binding of the target protein to the aptamer, the aptamer dissociates from the surface leading to enhancement of the electron transfer which represent the basis of the detection. The aptamer adsorption, sensors responses and selectivity of the different nanomaterials were compared showing better performance of the SWCNT-based sensor. The voltammetric SWCNT aptasensors showed high sensitivity and selectivity with detection limits of 0.13 pg/mL and 0.03 pg/mL for total haemoglobin (tHb) and HbA1c, respectively. The aptasensor showed selectivity against other proteins in the blood including cystic fibrosis transmembrane conductance regulator (CFTR), survival motor neuron (SMN), dedicator of cytokinesis 8 (DOCK8), signal transducer and activator of transcription 3 (STAT3). This SWCNT aptasensor was superior to the reported detection assays for HbA1c in terms of sensitivity, selectivity and cost. Moreover, our results demonstrate that the choice of the carbon nanomaterial can have a profound impact on the biosensing performance.

Interdiffusing core-shell nanofiber interleaved composites for excellent Mode I and Mode II delamination resistance

Electrospun nanofibre interleaving has a great potential for toughening of composite laminates as an effective, safe and industrially relevant method. Although many studies showcase large increases in delamination resistance, these are typically obtained under either Mode I or Mode II loading and for a wide variety of nanofibres. Here, we present a more general approach towards simultaneous excellent Mode I and Mode II delamination resistance using a single nanofibre system without the need for additional chemical modification steps or speciality polymers. It is illustrated based on the concept of interdiffusion of polycaprolactone nanofibres during the curing process into the epoxy matrix resin for improved adhesion. The results show that for a simultaneous increase in Mode I and Mode II delamination resistance, the adhesion and the fibre morphology of the nanofibres are crucial. The methodology is then expanded to allow for industrial relevant working windows by core-shell structured polyamide/polycaprolactone nanofibres. This approach results in a GIc of 650 ± 50 J m-2 (+ca. 60% vs. virgin material) and a GIIc of 3160 ± 35 J m-2 (+ca. 60% vs. virgin material).

Bacteria-Responsive Single and Core-Shell Nanofibrous Membranes Based on Polycaprolactone/Poly(ethylene succinate) for On-Demand Release of Biocides.

Traditional antibacterial dressings continuously elute biocides, even if there are no bacteria. This unneeded release can cause cytotoxicity, increase costs, and delay healing. We designed a bacteria-responsive nanofibrous wound dressing, which can be degraded in the presence of bacteria to release antimicrobial agents. A model biocide, benzyl dimethyl tetradecyl ammonium chloride (BTAC), was incorporated into bacteria-degradable polymers [polycaprolactone and poly(ethylene succinate)] in two ways: evenly distributed inside the polymers as single nanofibers and encapsulated in a core surrounded by the same polymers as core–shell nanofibers. Because of bacterial activity (both lipase secretion and acidic pH), degradation of the fibers was facilitated and caused the release of incorporated BTAC. BTAC-loaded single and core−shell nanofibers presented >1 log reduction of both Staphylococcus aureus and Escherichia coli within 2 h. Additionally, the core–shell structure provided a more controlled release of BTAC with prolonged antibacterial properties than single nanofibers. The core–shell nanofibers also exhibited minimal cytotoxicity against human fibroblast cells (>80% viable cells after 24 h contact). These nanofibrous mats have the potential to selectively release antibacterial agents to prevent wound infections without delaying wound healing.

Gas Sensors Based on Nano/Microstructured Organic Field-Effect Transistors.

Benefiting from the advantages of organic field-effect transistors (OFETs), including synthetic versatility of organic molecular design and environmental sensitivity, gas sensors based on OFETs have drawn much attention in recent years. Potential applications focus on the detection of specific gas species such as explosive, toxic gases, or volatile organic compounds (VOCs) that play vital roles in environmental monitoring, industrial manufacturing, smart health care, food security, and national defense. To achieve high sensitivity, selectivity, and ambient stability with rapid response and recovery speed, the regulation and adjustment of the nano/microstructure of the organic semiconductor (OSC) layer has proven to be an effective strategy. Here, the progress of OFET gas sensors with nano/microstructure is selectively presented. Devices based on OSC films one dimensional (1D) single crystal nanowires, nanorods, and nanofibers are introduced. Then, devices based on two dimensional (2D) and ultrathin OSC films, fabricated by methods such as thermal evaporation, dip-coating, spin-coating, and solution-shearing methods are presented, followed by an introduction of porous OFET sensors. Additionally, the applications of nanostructured receptors in OFET sensors are given. Finally, an outlook in view of the current research state is presented and eight further challenges for gas sensors based on OFETs are suggested.

Frequency-Dependent Effective Capacitance of Supercapacitors Using Electrospun Cobalt-Carbon Composite Nanofibers

Mixing carbon-based materials with pseudocapacitive material is a widely used strategy to prepare high-energy, high-power supercapacitors. However, phase separation is inevitable after extended charging/discharging which leads to the degradation of performance metrics of the device. Here, we prepare in a single step cobalt-incorporated carbon nanofibers (CNF) by electrospinning homogeneous solutions of polyacrylonitrile (PAN) with cobalt acetate at different nominal proportions (1:0 to 1:1), and investigate their stability and capacitive behavior in symmetric supercapacitors. The electrochemical analyzes demonstrated up to an order of magnitude increase in the effective capacitive with increasing the cobalt content at both close-to-dc frequencies and at around 50/60 Hz power line frequencies. The maximum capacitance is recorded for a nominal cobalt acetate-to-PAN ratio of 0.9 (e.g. 29, 27, 22 and 10 mF at 0.01. 0.1, 1 and 100 Hz respectively; both electrodes are loaded with 1 mg cm− 2 of active material each). All devices showed also an outstanding capacitance retention exceeding 99% for 10000 cycles at 1 mA and 5 mA charging/discharging rates each. The improved energy storage capabilities are attributed to both the increased electrical conductivity and high pyridinic nitrogen content which was revealed from the material characterization results using XRD, FE-SEM/TEM, and XPS.

Evaluation of Mechanical Properties of Dimpled PET Fiber Fabricated by Electrospinning Method

Insufficient endothelialization of stent grafts tends to cause a problem of thrombosis formation. Because the structure of nanofibers, generally defined as fibers with a diameter below 1 μm, resembles the structure of an extracellular matrix, nanofibers are applied to scaffolds for regenerative medicine. Using nanofibers as the covering material of the stent graft can be expected to solve the problem of the stent graft. Previous studies have shown that a porous scaffold offers better surfaces to anchor and culture endothelial cells than a nonporous scaffold. Therefore, fibers with nanoorder dimples are expected to promote endothelialization. As a method of forming the dimple shape on the surface of the PET fiber, there is a method utilizing a difference in the volatilization rate of the solvent in the high humidity environment in the electrospinning method. For practical application of the stent graft to artificial blood vessels, the mechanical properties of the dimpled PET fiber should be clarified. In this study, the mechanical properties of single nanofibers and nonwoven fabrics of PET fibers with dimples on their surface were evaluated by tensile test. By forming the dimple shape on the fiber surface, the tensile strength of single PET fibers with dimples was 90 % lower than that of single PET fibers with a smooth surface. In the fabrication process of nonwoven fabric, the addition of EG delayed the volatilization of the PET solution, and the fibers adhered to each other. The bonding between the fibers contributed to the tensile strength of the nonwoven fabric.

Electrospinning of Ag/ZnWO4/WO3 composite nanofibers with high visible light photocatalytic activity

Distinctive Ag/ZnWO4/WO3 composite nanofibers have been successfully synthesized by a simple electrospinning method followed by subsequent annealing treatment. The as-prepared composite nanofibers are systematically characterized by SEM, XRD, XPS, UV–vis DRS and PL spectra. The photocatalytic activity of Ag/ZnWO4/WO3 composite nanofibers to the degradation of Methyl Blue (MB) is evaluated under UV–vis light irradiation. The result shows that the photocatalytic degradation rate of Ag/ZnWO4/WO3 composite nanofibers reaches to 94% within 80 min, which is higher than that of single WO3 nanofibers and Ag/WO3 binary composite nanofibers. The enhanced photocatalytic efficiency of Ag/ZnWO4/WO3 composite nanofibers is attributed to the synergistic effect of three different activated materials.

Conduction mechanisms in lanthanum manganite nanofibers

Lanthanum manganites are being constantly investigated for their interesting magnetic and transport properties. In this study, polycrystalline, single phase lanthanum manganite (LaMnO3) nanofibers were synthesized using an electrospinning technique, and characterized in terms of phase, microstructure, ac and dc electrical properties. X-ray diffraction and scanning electron microscopy revealed the formation of uniform composite nanofibers (average dia.∼ 600 nm) at 100 °C and polycrystalline single phase porous LaMnO3 nanofibers (average dia.∼ 400 nm) when calcined at 600 °C. Temperature dependent impedance and current-voltage (IV) characteristics of LaMnO3 nanofibers deposited on an interdigitated electrode type device, were investigated at temperatures ranging from 298 to 378 K. The observed decrease in the dielectric constant at high frequencies may be due to decrease in the contribution from dipolar polarization. Analysis of ac conductivity indicated thermally activated type conduction mechanism in these nanofibers which could be explained by a correlated barrier hopping (CBH) model. The observed decreasing trend in activation energy with increasing frequency also supported the CBH model. Furthermore, the analysis of log (J) vs. E0.5 curves at different temperatures showed a large difference of ~5.82 between the experimental and theoretical field lowering coefficient with an internal field enhancement factor of α2 = 33.91. This result excluded the possibility of Pool-Frenkel type conduction and the observed variation might be due to the presence of some localized electric fields. Further investigation of IV characteristics revealed that the ‘space-charge-limited current (SCLC) with traps’ may be the possible conduction mechanism.

Direct Growth of CoFe2 Alloy Strongly Coupling and Oxygen‐Vacancy‐Rich CoFe2O4 Porous Hollow Nanofibers: an Efficient Electrocatalyst for Oxygen Evolution Reaction

AbstractEfficient electrocatalysts for the oxygen evolution reaction (OER) is crucial for improving the performance of metal−air batteries and water splitting. In this study, the CoFe2 alloy strongly coupling and oxygen‐vacancy‐rich CoFe2O4 (CoFe2 alloys/CoFe2O4) porous hollow complex nanofibers, as a highly efficient and stable electrocatalyst for OER, have been synthesized via a facile method of electrospinning combining with two‐step heat treatment. The obtained CoFe2 alloys/CoFe2O4 porous hollow complex nanofibers show high electrical conductivity with the smaller charge transfer resistance than that of the commercial RuO2, and even two orders of magnitude lower than that of the single CoFe2O4 porous hollow nanofibers. When used as an electrocatalyst for OER, it demonstrates a superior electrochemical performance with an over‐potential of 300 mV at the current density of 10 mA cm−2, which is comparable to that of the commercial RuO2 but obviously better than that of the single CoFe2O4 porous hollow nanofibers. Moreover, the CoFe2 alloys/CoFe2O4 porous hollow complex nanofibers exhibit remarkably stability with negligible potential increase of only 1.2 % at high current density of 100 mA cm−2 for 16 h. Meanwhile, the CoFe2 alloys/CoFe2O4 porous hollow complex nanofibers also show an excellent hydrogen evolution reaction (HER) activity, affording an over‐potential of 152 mV at the current density of 10 mA cm−2. When using for water splitting in 1 M KOH, the CoFe2 alloys/CoFe2O4 porous hollow complex nanofibers delivers a current density of 10 mA cm−2 at a cell voltage of 1.687 V. More important, the direct growth of CoFe2 alloys on the CoFe2O4 base of the porous hollow nanofibers can be an effective way to control the coupling of the CoFe2 alloys and CoFe2O4, the electronic conductivity and the active sites, and then the electrochemical performance of OER.

Correlating diameter, mechanical and structural properties of poly(l-lactide) fibres from needleless electrospinning

The development and application of nanofibres requires a thorough understanding of the mechanical properties on a single fibre level including respective modelling tools for precise fibre analysis. This work presents a mechanical and morphological study of poly-l-lactide nanofibres developed by needleless electrospinning. Atomic force microscopy (AFM) and micromechanical testing (MMT) were used to characterise the mechanical response of the fibres within a diameter range of 200–1400 nm. Young’s moduli E determined by means of both methods are in sound agreement and show a strong increase for thinner fibres below a critical diameter of 800 nm. Similar increasing trends for yield stress and hardening modulus were measured by MMT. Finite element analyses show that the common practice of modelling three-point bending tests with either double supported or double clamped beams is prone to significant bias in the determined elastic properties, and that the latter is a good approximation only for small diameters. Therefore, an analytical formula based on intermediate boundary conditions is proposed that is valid for the whole tested range of fibre diameters, providing a consistently low error in axial Young’s modulus below 10%. The analysis of fibre morphology by differential scanning calorimetry and 2D wide-angle X-ray scattering revealed increasing polymer chains alignment in the amorphous phase and higher crystallinity of fibres for decreasing diameter. The combination of these observations with the mechanical characterisation suggests a linear relationship between Young’s modulus and both crystallinity and molecular orientation in the amorphous phase. Statement of significanceFibrous membranes have rapidly growing use in various applications, each of which comes with specific property requirements. However, the development and production of nanofibre membranes with dedicated mechanical properties is challenging, in particular with techniques suitable for industrial scales such as needleless electrospinning. It is therefore a key step to understand the mechanical and structural characteristics of single nanofibres developed in this process, and to this end, the present work presents changes of internal fibre structure and mechanical properties with diameter, based on dedicated models. Special attention was given to the commonly used models for analyzing Young’s modulus of single nanofibers in three-point bending tests, which are shown to be prone to large errors, and an improved robust approach is proposed.

The formation of highly ordered graphitic interphase around embedded CNTs controls the mechanics of ultra-strong carbonized nanofibers

Templating graphitization, i.e., the transformation of certain polymers to highly-ordered graphitic (HOG) domains upon pyrolysis in the vicinity of graphitic nanomaterials, such as carbon nanotubes (CNTs), is known to be an effective approach to modify the microstructure of carbon nanofibers (CNFs). In this work, the microstructure of CNFs subjected to the templating effect of functionalized single-walled CNTs (f-SWNTs) and the effect of templating on mechanical properties of CNF/f-SWNTs hybrid nanofiber are studied. The CNF/f-SWNTs were fabricated via pyrolysis of electrospun polyacrylonitrile precursors with CNT inclusions. Prior to pyrolysis, the precursors were subjected to thermomechanical treatments, known as hot-drawing, to enhance chain and CNT alignment and packing. The study of the microstructure of the precursor and CNFs indicates the crucial role of precursor hot-drawing in enhancing the microstructure of the precursor and CNFs, leading to drastically enhanced templating effect, as evidenced from the thickness of the HOG that forms around CNTs. Mechanical tests on single nanofibers using custom-designed microdevices led to the realization that the templating effect of CNTs on CNFs, when properly implemented via precursor hot-drawing, can considerably increase the strength of CNFs. The average tensile strength and modulus of CNF/f-SWNTs in which HOG domains had clearly formed were measured to be 7.6 and 268 GPa, respectively, which are the highest value reported to date among similar types of materials. The existence and evolution of the HOG around CNTs inside CNFs and mechanical reinforcing of HOG were thoroughly discussed in conjunction with finite element models of building blocks of CNFs, alluding to the stress fields around HOG and CNTs in the CNF. The high-performance 1-D hybrid graphitic nanostructure developed here, CNF/f-SWNTs, can serve as an outstanding reinforcement material for weight sensitive applications.

Magnetization reversal in bent nanofibers of different cross sections

Ferromagnetic nanofibers and nanofiber based networks with new electronic, magnetic, mechanical, and other physical properties can be considered significant components of bio-inspired cognitive computing units. For this purpose, it is necessary to examine all relevant physical parameters of such nanofiber networks. Due to the more or less random arrangement of the nanofibers, first of all, the elementary single nanofibers with varying bending radii, from straight fibers to those bent along half-circles, were investigated by micromagnetic simulations, using different angles with respect to the external magnetic field. Different fiber cross sections, i.e., circular, circle-segment, rectangular, significantly altered the coercive fields and their dependence on the bending radius, for the magnetic field oriented differently in relation to the fiber axes. The shapes of the longitudinal and transverse hysteresis curves showed strong differences, depending on cross section, bending radius, and orientation to the magnetic field, often depicting distinct transverse magnetization peaks perpendicular to the fibers for fibers which were not completely oriented parallel to the magnetic field. Varying these parameters thus provides a broad spectrum of magnetization reversal processes in magnetic nanofibers and correspondingly scenarios for a variety of fiber-based information processing.

Carbon Nanofiber and Meldola Blue Based Electrochemical Sensor for NADH: Application to the Detection of Benzaldehyde

AbstractNanomaterials used in tandem with electrochemical mediators on screen‐printed electrodes enable sensitive, low cost detection of NADH with minimal interferences in real‐world samples. In this work we investigated the combination between the mediator Meldola Blue and several types of commercial screen‐printed carbon electrodes, i. e. modified with mesoporous carbon, single wall carbon nanotubes, graphene or carbon nanofibers (CNF) as NADH detectors. The sensors were compared with bare carbon electrodes and with commercially available Meldola Blue‐modified electrodes. The best sensitivity for NADH detection by amperometry was observed for Meldola Blue/CNF electrodes, and further improvement was obtained by mixing the mediator with graphene oxide prior to dropcasting. The “MB‐erGO/CNF” sensors obtained were characterized by a detection limit of 0.5 μM, a linear range of 1–300 μM and a sensitivity of 80.0±2.5 μA cm−2 mmol−1 L, 10 times higher than that of commercial sensors. While the use of graphene oxide lead to enhanced sensitivity and wider linear range, it didn't improve the operational stability as the mediator gradually desorbed from the electrodes. Furthermore, the sensors were coupled with a new NAD+‐dependent aldehyde dehydrogenase from a psychrophilic bacterium for the analysis of benzaldehyde and proven to be advantageous over commercial electrodes with Meldola Blue in circumstances where the detection was limited by NADH detection, i. e. at pH 9.5.

Effective Formation of Well-Defined Polymeric Microfibers and Nanofibers with Exceptional Uniformity by Simple Mechanical Needle Spinning.

The fabrication of nanofibers with a mechanical force has attracted increasing attention owing to its facile and easy fabrication. Herein, we demonstrate a novel and facile fabrication technique with the mechanical force, needle spinning, which utilizes a needle tip to draw a polymer solution to form fibrous structures. We studied the effect of the processing parameters to the nanofiber structure, namely, the pulling away speed, pulling away distances, needle size, and polymer concentration, which were systemically controlled. As the needle spinning provides an effective route to adjust those parameters, highly uniform nanofibers can be achieved. There are clear tendencies in the diameter; it was increased as the polymer concentration and needle size were increased, and was decreased as the pulling away distance and pulling away speed were increased. Needle spinning with a precise control of the processing parameter enables us to readily fabricate well-defined nanofibers, with controlled dimensions in diameter and length; plus, single nanofibers also can be easily formed. Those features cannot be realized in common spinning process such as electrospinning. Therefore, this technique will lead to further development of the use of mechanical force for nanofiber fabrication and will expand the range of nanofibers applications.

Nanofiber-Directed Anisotropic Self-Assembly of CdSe-CdS Quantum Rods for Linearly Polarized Light Emission Evidenced by Quantum Rod Orientation Microscopy.

Hybrid soft materials composed of CdSe-CdS nanorods or "quantum rods" (QRs) and the fluorescent 2,3-didecyloxyanthracene (DDOA) low molecular weight organogelator are obtained through self-assembly. Spectroscopy, microscopy, and rheology studies show that the QRs and DDOA coassemble, thereby stabilizing the organogels. Depending on the QR load and excitation wavelength, single nanofibers (NFs) of the hybrid gel display either sharp polarized red luminescence (under green excitation), or dual perpendicularly polarized blue and red emissions (under UV excitation). Transmission electron microscopy, microspectroscopy, and quantum rod orientation microscopy (QROM) reveal that QRs align along the organogel NFs with order parameters reaching 76% and 87%. This paves the way for obtaining surfaces of QR/NF assemblies yielding sharp red linearly polarized emission. In addition, this work demonstrates that QRs can be used more generally to probe nanostructured soft materials, even nonemissive ones. QROM allows to establish maps of the orientation of single QRs dispersed onto or within a gel network by measuring the polarization of the emission of the individual QRs. As occurs within this work in which QRs and NFs interact, the orientation of each QR reveals information on the underlying nanostructure (such as surface striation, bundle formation, and helicity).

High-Q, low-index-contrast photonic crystal nanofiber cavity for high sensitivity refractive index sensing.

We present the design of simultaneous high-quality (Q)-factor and high-sensitivity (S) photonic crystal nanofiber cavities (PCNFCs) made of single silica nanofiber that have a low-index contrast (ratio=1.45). By using the three-dimensional finite-difference time-domain method, two different resonant modes, dielectric mode (DM) and air mode (AM), are designed and optimized to achieve an ultrahigh figure of merit (FOM), respectively. Numerical simulations are performed to study the Q-factors and sensitivities of the proposed PCNFCs. It shows that for both DM- and AM-based PCNFCs, respectively, the Q-factors and sensitivities of Q∼1.1×107, S=563.6 nm/RIU and Q∼2.1×105, S=736.8 nm/RIU can be estimated, resulting in FOMs as high as 4.31×106 and 1.13×105, respectively. To the best of our knowledge, this is the first silica nanofiber cavity geometry that simultaneously features high Q and high S for both DM and AM in PCNFCs. Compared with the state of the art of nanofiber-based cavities, the cavity Q-factor to mode volume (V) ratio (Q/V) in this work has been improved more than two orders of magnitude. The demonstration of a high Q/V cavity in low-index-contrast nanofibers can open up versatile applications using a broad range of functional and flexible fibers. Moreover, due to the extended evanescent field and small mode volumes, the proposed PCNFCs are ideal platforms for remote ultra-sensitive refractive-index-based gas sensing without the need for complicated coupling systems.

Novel fabrication of extremely high aspect ratio and straight nanogap and array nanogap electrodes

We reported a reproducible, simple and novel method for fabricating electrodes with high aspect ratio and highly straight nanometer size gap. The gap size could be controlled in a wide range between several nm up to several hundreds of nm, although in this work our individual gap size was 172 nm. In this method a single nanofiber was aligned as a sacrificial structure using a secondary electrical field and its diameter lowered through thermal treatment to obtain smallest gap size. Then, after deposition of blanket metal, nanofiber was removed obtaining nano scale gap. We predict the application of these simple fabricated gaps for diverse fields. The expensive, time consuming, none-reproducible and low accuracy fabrication methods can supersede by this cost effective, facile and fast method. It can provide mass production for precisely positioned nanoscale gaps, ignoring electrode and substrate materials. The electrodes hold the advantage of maximum straightness comparing to other similar nano fabrication methods. Fabricated gaps have large aspect ratio (in the order of 106). Also array gaps with average gap size of 400 nm were fabricated. Same size gaps could be fabricated in a row by this method. Different parameters in alignment were taken into account and studied. The process shows great potential for facile and batch fabrication of parallel submicron gaps for diverse applications including gas sensing, bio-sensing and nanofluidic systems.

Synthesis and ac electrical characterization of nickel oxide nanofibers

In this study, we present the synthesis of nickel oxide nanofibers through electrospinning technique at optimum processing and heat treatment conditions. The diameter and uniformity of electro-spun nickel oxide nanofibers were investigated as a function of PVP concentration. Uniform and homogeneous composite nanofibers were observed for PVP:Ni(CH3COO)2·H2O ratio of 1:1. X-ray diffraction and scanning electron microscopy of samples calcined at 600 °C revealed the formation of uniform but porous single phase nickel oxide nanofibers of an average diameter Electrical properties of nickel oxide nanofibers, obtained at optimum conditions, were studied using inter-digitated electrodes type device. Temperature-dependent impedance spectroscopy revealed different electro-active regions (grain and grain boundaries) and their activation energies were 0.24 and 0.36 eV, respectively. These results suggested less resistive grain than grain boundary in the employed temperature range, and hence, two different transport mechanisms.