Ilias Louis Kyratzis

Carbon Nanotube Webs: A Novel Material for Sensor Applications

Since their discovery in 1991 by Iijima, [ 1 ] carbon nanotubes (CNTs) have attracted intensive research and investigation due to their unique electrical, mechanical, structural, and chemical properties. [ 2 , 3 ] Their novel properties make them attractive for fabricating electrochemical sensors and biosensors. Several compounds have been reported to undergo improved electrochemical reactions at the CNT surface, such as cytochrome c, [ 4 ]

Bioremediation of pesticide contaminated water using an organophosphate degrading enzyme immobilized on nonwoven polyester textiles

Bioremediation using enzymes has become an attractive approach for removing hazardous chemicals such as organophosphate pesticides from the environment. Enzymes immobilized on solid carriers are particularly suited for such applications. In this study, the organophosphate degrading enzyme A (OpdA) was covalently immobilized on highly porous nonwoven polyester fabrics for organophosphate pesticide degradation. The fabrics were first activated with ethylenediamine to introduce free amine groups, and the enzyme was then attached using the bifunctional crosslinker glutaraldehyde. The immobilization only slightly increased the Km (for methyl parathion, MP), broadened the pH profile such that the enzyme had significant activity at acidic pH, and enhanced the stability of the enzyme. The OpdA-functionalized fabrics could be stored in a phosphate buffer or in the dry state at 4°C for at least 4 weeks without a large loss of activity. When used in batch mode, the functionalized textiles could degrade 20 μM MP in un-buffered water at liquor to fabric ratios as high as 5000:1 within 2h, and could be used repeatedly. The fabrics could also be made into columns for continuous pesticide degradation. The columns were able to degrade 50 μM MP at high flow rates, and could be used repeatedly over 2 months. These results demonstrate that OpdA immobilized on nonwoven polyester fabrics is useful in environmental remediation of organophosphate compounds.

Effect of viscosity and electrical conductivity on the morphology and fiber diameter in melt electrospinning of polypropylene

The feasibility of fabricating polypropylene (PP) nanofibers has been explored by using different additives, such as sodium oleate (SO), poly(ethylene glycol) (PEG) and poly(dimethyl siloxane) (PDMS), during melt electrospinning. PP of high melt flow index (1000) was used with PEG and PDMS for the reduction of the melt viscosity; and it was used with SO for improving the electrical conductivity during melt electrospinning. It was observed that all the additives used in this study helped to reduce the fiber diameter. The most promising additive, SO, was effective in reducing the fiber diameter to the nanometer scale due to the increase in the electrical conductivity. The fiber diameter was decreased by the addition of PEG and PDMS due to the decrease in the melt viscosity. The effect of die shape on the fiber cross-sectional shape was analyzed and an interesting finding is that the die shapes did not have an effect on the cross-sectional shape of the fibers. That is, irrespective of the die shapes (i.e. trilobal, tetralobal, multilobal and circular) used in this study, the cross-sectional shapes of melt electrospun fibers were circular. The distribution of the additives in the fiber was analyzed by energy-dispersive X-ray analysis and was found to be uniform. Tensile tests were performed on single nanofibers with limited success, due to the problems in preparing fiber samples and successfully holding them in the jaws of the testing machine without slippage.

Immobilization of Acetylcholinesterase onto Carbon Nanotubes Utilizing Streptavidin-biotin Interaction for the Construction of Amperometric Biosensors for Pesticides

Abstract Carbon nanotubes (CNTs) are very promising materials onto which bioactive molecules can be immobilized in the construction of biosensors. Streptavidin was used as a molecular linker to immobilize biotinylated acetylcholinesterase (AChE) on CNTs in a gentle and controllable fashion for pesticide biosensors. Glassy carbon electrodes coated with the CNT-enzyme complex had high affinity for the substrate acetylthiocholine and produced strong peak oxidation currents in electrochemical assays. We also propose a new method, i.e., the use of relative net slope rather than the percentage of inhibition, in the calculation of pesticide concentrations. The biosensors could detect low levels of the pesticide methyl paraoxon.

Continuous Production of Flexible Fibers from Transgenically Produced Honeybee Silk Proteins

Flexible and solvent stable fibers are produced after concentrated recombinant honeybee protein solutions are extruded into a methanol bath, dried, drawn in aqueous methanol, then covalently cross-linked using dry heat. Proteins in solution are predominantly coiled coil. Significant levels of non-orientated ß-sheets form during drying or after coagulation in aqueous methanol. Drawing generally aligns the coiled coil component parallel with the fibre axis and ß-sheet component perpendicular to the fiber axis. The fibres are readily handled, stable in the strong protein denaturants, urea and guanidinium, and suitable for a range of applications such as weaving and knitting.

High surface area mesoporous titanium–zirconium oxide nanofibrous web: a heavy metal ion adsorbent

A mixed titanium–zirconium (Ti :  Zr = 2 : 1 atomic ratio) oxide non-woven nanofibrous web was prepared by using an electrospinning technique followed by thermal treatment. A hydrocarbon surfactant was incorporated into the electrospinning solution and was pyrolysed during heating. The surfactant acted as a structure-directing agent to create intra-fibre pores, and significantly increased the surface area of the fibres, thereby maximising the number of sites for further surface modification as well as heavy metal ion adsorption. The high surface area (248 m2 g−1) titanium–zirconium oxide nanofibre surface was functionalised via a phosphonic acid coupling reaction to give different functional groups for attracting metal ions (i.e., phosphonate and amine groups). The cadmium adsorption capacity of the phosphonate-functionalised nanofibres was up to 10 times higher than that of the non-modified or amine-functionalised nanofibres. In addition, the cadmium adsorption on the phosphonate-functionalised nanofibres was less dependent on the pH of analyte solutions than the metal oxide nanofibres where the surface charge changed in varied pH environments. The size of the nanofibrous web can be easily scaled for making a large web convenient for handling and recovery after use, compared with high surface area heavy metal ion adsorbents that are nanometre or micrometre in size.

Enhanced photocatalytic activity: Macroporous electrospun mats of mesoporous au/TiO2 nanofibers

An electrospinning technique coupled with sol–gel chemistry is applied for the one‐pot preparation of macroporous–mesoporous titanium dioxide nanofibrous mats embedded with Au nanoparticles. This facile approach produces nanofibers that are thermally treated to simultaneously 1) remove the organics, 2) reduce AuIII to Au0 to form Au nanoparticles, and 3) crystallize titania to the anatase phase. This methodology allows high‐temperature treatment (650 °C) for well‐crystallized titania without agglomeration of the nanoparticulate Au (13±3 nm), which thereby significantly advances the existing methods for the synthesis of Au/TiO2 materials for which multiple steps are required. Additionally, high Au yields (≈100 %) were achieved in the final structure, which demonstrates another merit of this technique. The X‐ray diffraction patterns of the nanofibers were monitored by using a synchrotron beamline as the sample was heated to determine the optimum calcination temperature required to maximize the anatase phase and minimize the formation of rutile. Both the material properties (which include morphology, pore size distribution, surface area, Au particle size, and TiO2 crystal phase and size) and photocatalytic activity can be readily tuned as a function of the calcination temperature and Au content. The material calcined at 550 °C with 2.0 wt % Au shows the highest photocatalytic activity. This material is anatase in phase (which maximizes the electron‐transfer activity) and has the highest loading of small Au nanoparticles (which act as electron sinks to decrease the recombination of photo‐excited electrons and holes). These Au/TiO2 nanofibrous mats have the advantage of easy recovery and, therefore, reuse after the photocatalytic reaction, which addresses the issue of photocatalyst separation when using nanoparticulate powders as photocatalysts.

Application of Carbon Nanotubes in the Extraction and Electrochemical Detection of Organophosphate Pesticides: A Review

Recent trends and challenges in developing carbon nanotubes (CNT) based sensors and biosensors for the detection of organophosphate (OP) pesticides and other organic pollutants in water are reviewed. CNT have superior electrical, mechanical, chemical, and structural properties over conventional materials such as graphite. At the same time CNT based sensors and biosensors are more efficient compared to the existing traditional techniques such as high-performance liquid chromatography or gas chromatography, because they can provide rapid, sensitive, simple, and low-cost on-field detection. The measurement protocols can be based on enzymatic and non-enzymatic detection. The enzyme acetylcholinesterase (AChE) is used with CNT for fabricating ultrasensitive biosensors for OP detection involving different immobilization schemes such as adsorption, crosslinking, and layer-by-layer self-assembly. This protocol relies on measuring the degree of enzyme inhibition as means of OP quantification. The other enzyme used along with CNT for OP detection is organophosphate hydrolase (OPH) which hydrolyzes the OP into detectable species that can be measured by amperometric or potentiometric methods. Different forms of CNT electrode materials can be used for fabricating such electrodes such as pure CNT and composite CNT. Due to their large surface area and hydrophobicity, CNT have also been used for the extraction and non-enzymatic electrochemical detection of OP with very high efficiency. The application of CNT and their novel properties for the adsorption and electrochemical detection of OP compounds is discussed in detail.

A comparison of the effects of fibre alignment of smooth and textured fibres in electrospun membranes on fibroblast cell adhesion.

A polyester polycaprolactone-based polyurethane elastomer (PU) and poly-(l-lactide) (PLLA), two common biomaterials, were electrospun to produce membranes with fibres either randomly orientated or aligned. PU was used to produce membranes consisting of smooth fibres. PLLA was used to prepare fibres with a textured surface. Contact angle measurements of the PU and PLLA cast films reveal that they were both below 90 degrees and fully wetted in less than 60 s. These membranes were investigated for the effect of fibre topography and fibre alignment on cell adhesion, using mouse L929 fibroblasts. It was found that the alignment of electrospun fibres controls the directional spreading of fibroblast independent of fibre being smooth or textured.

Fabrication and Characterisation of Nanofibres by Meltblowing and Melt Electrospinning

Fabrication of nanofibres has become a growing area of research because of their unique properties (i.e. smaller fibre diameter and higher surface area) and potential applications in various fields such as filtration, composites and biomedical applications. Although several processes exist for fabrication of nanofibres, electrospinning is considered to be the simplest. Most of the research in electrospinning is based on solution rather than melt. The feasibility of fabricating nanofibres of polypropylene (PP) by meltblowing and melt electrospinning has been investigated in this paper. In meltblowing different fluids such as air and water were fed at different inlets along the extrusion barrel for the fabrication of nanofibres whereas in melt electrospinning it was achieved by using different additives. The results obtained by using water in meltblowing were better with respect to the morphology and fibre uniformity compared to air. In melt electrospinning although all the additives (i.e. sodium oleate (SO), polyethylene glycol (PEG) and polydimethyl siloxane (PDMS)) helped in reducing the fibre diameter, only SO was effective to reduce the diameter down to nanoscale. It was concluded that both the solvent-free processes have the potential to substantially increase the production of nanofibres compared to solution electrospinning.