Lynam C, Jennings K, Nolan K, Kane P, McKervey MA, Diamond D (2002) Tuning and enhancing enantioselective quenching of calixarene hosts by chiral guest amines., Anal Chem 74 (1) pp. 59-66
The synthesis of a propranolol amide derivative of p-allylcalixarene is described, which has been designed to behave as a molecular sensor capable of distinguishing chiral amines on the basis of their shape and chirality. This molecule can discriminate between the enantiomers of phenylalaninol through the quenching of the fluorescence emission in methanol in contrast to an (S)-dinaphthylprolinol calixarene derivative, which can discriminate between the enantiomers of phenylglycinol, but not phenylalaninol. The separation between the naphthyl fluorophores and the hydrogen-bonding sites within the chiral cavity can be tuned to recognize guest amines with similar separation between aryl groups and hydrogen-bonding sites. The formation of metal ion complexes of the p-allylcalixarene propranolol amide derivative is shown to induce a more regular and rigid cone conformation in the calixarene macrocycle, which generates a significant enhancement in the observed enantiomeric discrimination.
Viguier C, Crean C, O'Kennedy R (2012) Trends and perspectives in immunosensors, pp. 184-208
Immunosensors are devices that comprise both a biomolecular recognition system, such as an antibody and its corresponding antigen, and a transducer to translate the high affinity and specific binding event into a physical signal. Antibodies are produced by an immunological response to the presence of a foreign substance called an antigen. Antibodies may be immobilised onto a variety of platforms including bulk planar surfaces and nanoparticles by either covalent or adsorption strategies. Different interfaces between the biocomponents and the detector are available to monitor in 'real-time' the signal generated by biological interactions. The transducers detect, for example, the change in electron transfer, absorbance, fluorescence, refractive index, mass change or heat transfer as the antibody binds to the antigen of interest. Such analytical devices have allowed a wide range of analytes to be identified and quantified such as pathogens, toxins, environmental food contaminants and disease biomarkers. The demand for sensitive, rapid, and 'on-site' techniques has taken advantage of the latest advances in microfluidics and nanotechnology. This chapter will highlight current trends in immobilisation, micro/nano-fluidics/and transducers utilised. A number of examples outlining the exploitation of these elements in immunosensors and their successful applications will be described. © 2012 Bentham Science Publishers. All rights reserved.
Chen J, Wang JZ, Minett AI, Liu Y, Lynam C, Liu H, Wallace GG (2009) Carbon nanotube network modified carbon fibre paper for Li-ion batteries, ENERGY & ENVIRONMENTAL SCIENCE 2 (4) pp. 393-396 ROYAL SOC CHEMISTRY
Wallace GG, Ngamna O, Moulton S, Lynam C (2005) Use of carbon nanotubes in modifying the properties of inherently conducting polymers, Meeting Abstracts pp. 377-377
Chen J, Minett AI, Liu Y, Lynam C, Sherrell P, Wang C, Wallace GG (2008) Direct growth of flexible carbon nanotube electrodes, ADVANCED MATERIALS 20 (3) pp. 566-+ WILEY-V C H VERLAG GMBH
Dechakiatkrai C, Chen J, Lynam C, Wetchakul N, Phanichphant S, Wallace GG (2009) Direct growth of carbon nanotubes onto titanium dioxide nanoparticles., J Nanosci Nanotechnol 9 (2) pp. 955-959
Multi-wall carbon nanotubes (MWNTs) were successfully deposited on a TiO2 nanoparticle film via thermal chemical vapour deposition (CVD) using iron(III) as the catalyst, which was loaded into the titanium isopropoxide precursor solution. The properties of the TiO2/MWNTs nanocomposite was characterized using Raman spectroscopy, scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX), 4-point probe conductivity measurements and cyclic voltammetry. Preliminary investigations on this TiO2/MWNTs nanocomposite as an anode material for Li-ion batteries shows a high reversible capacity of 268 mAh g(-1) with improved cycling stability compared with a mechanically blended composite.
Using facile diazonium chemistry, sulfonate groups have been covalently attached to single wall carbon nanotubes. The resulting sulfonated tubes form a stable aqueous dispersion in the presence of pyrrole monomer. Subsequent electropolymerisation results in a conductive, electroactive polypyrrole doped with sulfonated tubes being formed at unusually low potentials. The potential of this material as a host matrix for biomolecules has been demonstrated by entrapping horse-radish peroxidase directly in the polypyrrole during composite formation.
Moore CJ, Montón H, O'Kennedy R, Williams DE, Nogués C, Crean C, Gubala V (2015) Controlling colloidal stability of silica nanoparticles during bioconjugation reactions with proteins and improving their longer-term stability, handling and storage, Journal of Materials Chemistry B 3 (10) pp. 2043-2055 The Royal Society of Chemistry
Despite the potential of antibody-coated nanoparticles (Ab-NPs) in many biological applications, there are very few successful, commercially available examples in which the carefully engineered nanomaterial has made it beyond the laboratory bench. Herein we explore the robustness and cost of protein-nanoparticle conjugation. Using multivalent polyamidoamine (PAMAM) dendrimers and dextran as crosslinkers, it was possible to retain colloidal stability during (i) NP-linker binding and (ii) the subsequent conjugation reaction between linker-coated NPs and proteins to generate monodisperse Ab-NPs. This was attributed to the physicochemical properties of the linkers, which were inherited by the NPs and thus benefited colloidal stability. Attaching negatively charged, EDC/sulfo-NHS-activated PAMAM to the NPs contributed to overall negative charge of particles, and in turn led to high electrostatic attraction between the protein and PAMAM-coated NPs during the reaction conditions. In contrast, using an uncharged, EDC/NHS-activated PAMAM dendrimer led to NP aggregation and lower protein binding efficiency. Dextran as a cost-effective, uncharged macromolecule allowed for steric repulsions between neighbouring particles during protein binding, thus inducing NP stability in solution, and also produced monodisperse Ab-NPs. By freeze-drying Ab-NPs from a 1% BSA solution it is possible to reconstitute the solid-form colloid back to a stable state by adding solvent and simply shaking the sample vial by hand. The consequences of the different surface chemistries and freeze-drying stabilizers on the colloidal stability of the NPs were probed by dynamic light scattering. The performance of Ab-NPs was compared in a simple fluorescence linked immunoassay in whole serum. Interestingly, the signal-to-noise ratios were similar for Ab-NPs using PAMAM and dextran, despite dextran binding fewer Abs per NP. We believe this work provides researchers with the tools and strategies for reliably generating Ab-NPs that can be used for a variety of biological applications.
Pringle JM, Winther-Jensen O, Lynam C, Wallace GG, Forsyth M, MacFarlane DR (2008) I&EC 70-Ionic liquids for the synthesis of conducting polymer-noble metal nanocomposites, ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 236 AMER CHEMICAL SOC
The growing need for analytical devices requiring smaller sample volumes, decreased power consumption and improved performance have been driving forces behind the rapid growth in nanomaterials research. Due to their dimensions, nanostructured materials display unique properties not traditionally observed in bulk materials. Characteristics such as increased surface area along with enhanced electrical/optical properties make them suitable for numerous applications such as nanoelectronics, photovoltaics and chemical/biological sensing. In this review we examine the potential that exists to use nanostructured materials for biosensor devices. By incorporating nanomaterials, it is possible to achieve enhanced sensitivity, improved response time and smaller size. Here we report some of the success that has been achieved in this area. Many nanoparticle and nanofibre geometries are particularly relevant, but in this paper we specifically focus on organic nanostructures, reviewing conducting polymer nanostructures and carbon nanotubes.
Pringle JM, Winther-Jensen O, Lynam C, Wallace GG, Forsyth M, MacFarlane DR (2008) PMSE 431-Nanostructured conducting polymer synthesis in ionic liquids, ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 236 AMER CHEMICAL SOC
Li WH, Lynam C, Chen J, Liu B, Zhang XZ, Wallace GG (2007) Magnetorheology of single-walled nanotube dispersions, MATERIALS LETTERS 61 (14-15) pp. 3116-3118 ELSEVIER SCIENCE BV
Dechakiatkrai C, Lynam C, Chen J, Phanichphant S, Wallace GG (2008) Characterisation of Titanium Dioxide-Single Walled Carbon Nanotubes Composite Fibres Prepared by the Wet Spinning Technique, 2008 2ND IEEE INTERNATIONAL NANOELECTRONICS CONFERENCE, VOLS 1-3 pp. 134-139 IEEE
In this article, we report on poly(amidoamine) dendrimers (PAMAM) as coupling agents for recombinant single-chain (ScFv) antibodies to nanoparticle (NP) labels, for use in immunoassay. We present a simple theory for the kinetics of particle capture onto a surface by means of an antibody?antigen reaction, in which the important parameter is the fraction of the particle surface that is active for reaction. We describe how increasing the generation number of the linking dendrimers significantly increased the fraction of the NP surface that is active for antigen binding and consequently also increased the assay kinetic rates. Use of dendrimers for conjugation of the NP to the antibody resulted in a significantly higher surface coverage of active antibody, in comparison with mono-valent linker chemistry. As a direct consequence, the increase in effective avidity significantly out-weighed any effect of a decreased diffusion coefficient due to the NP, when compared to that of a molecular dye-labelled antibody. The signal to noise ratio of the G4.5 dendrimer-sensitised nanoparticles out-performed the dye-labelled antibody by approximately four-fold. Particle aggregation experiments with the multi-valent antigen CRP demonstrated reaction-limited aggregation whose rate increased significantly with increasing generation number of the dendrimer linker.
Lynam C, Minett AI, Habas SE, Gambhir S, Officer DL, Wallace GG (2008) Functionalising carbon nanotubes, INT J NANOTECHNOL 5 (2-3) pp. 331-351
INDERSCIENCE ENTERPRISES LTD
Pringle JM, Ngamna O, Lynam C, Wallace GG, Forsyth M, MacFarlane DR (2007) Conducting polymers with fibrillar morphology synthesized in a biphasic ionic liquid/water system, MACROMOLECULES 40 (8) pp. 2702-2711 AMER CHEMICAL SOC
Over the past decade, the design and development of wearable sensors for biomedical applications has garnered considerable attention in the scientifi c community and in industry. This chapter aims to review research conducted into wearable sensors for healthcare monitoring. Acceptance of this approach in observation of physiological data depends strongly on the cost, wearability, usability and performance of such devices. An outline of body sensor network systems (and applications of wearable computing devices) is provided with a summary of electronic textiles. A synopsis of the clinical applications of this type of technology is given at the end of the chapter © 2012 Woodhead Publishing Limited All rights reserved.
Dechakiatkrai C, Lynam C, Gilmore KJ, Chen J, Phanichphant S, Bavykin DV, Walsh FC, Wallace GG (2009) Single-Walled Carbon Nanotube/Trititanate Nanotube Composite Fibers, ADVANCED ENGINEERING MATERIALS 11 (7) pp. B55-B60 WILEY-V C H VERLAG GMBH
Pringle JM, Forsyth M, MacFarlane DR, Winther-Jensen O, Lynam C, Wallace GG (2008) One-step synthesis of conducting polymer-noble metal nanoparticle composites using an ionic liquid, Advanced Functional Materials 18 (14) pp. 2031-2040
Conducting polymers containing incorporated gold or silver nanoparticles have been synthesized using ionic liquid solutions of gold chloride or silver nitrate. Use of the metal salts as the oxidant for monomers such as pyrrole and terthiophene allows the composites to be formed in one simple step, without the need for templates or capping agents. The incorporated metal nanoparticles are clearly visible by TEM, and the composites have been further analyzed by TGA, CV, UV-Vis, Raman, XPS and scanning TEM coupled with EDS analysis. Utilization of an ionic liquid allows the full oxidizing power of the gold chloride to be accessed, resulting in incorporation of metallic gold into the polymers. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.
Lynam C, Moulton SE, Wallace GG (2007) Carbon-nanotube biofibers, ADVANCED MATERIALS 19 (9) pp. 1244-+ WILEY-V C H VERLAG GMBH
Sherrell PC, Chen J, Razal JM, Nevirkovets IP, Crean C, Wallace GG, Minett AI (2010) Advanced microwave-assisted production of hybrid electrodes for energy applications, ENERGY & ENVIRONMENTAL SCIENCE 3 (12) pp. 1979-1984 ROYAL SOC CHEMISTRY
Lee JW, Shin KM, Lynam C, Spinks GM, Wallace GG, Kim SJ (2008) The optimum functionalization of carbon nanotube/ferritin composites, SMART MATERIALS & STRUCTURES 17 (4) ARTN 045029 IOP PUBLISHING LTD
New energy storage devices are required to enable future technologies. With the rise of wearable consumer and medical devices, a suitable flexible and wearable means of storing electrical energy is required. Fibre-based devices present a possible method of achieving this aim. Fibres are inherently more flexible than their bulk counterparts, and as such can be employed to form the electrodes of flexible batteries and capacitors. They also present a facile possibility for incorporation into many fabrics and clothes, further boosting their potential for use in wearable devices.
Electrically conducting fibres were produced from a dispersion of carbon nanomaterials in a room temperature ionic liquid. Coagulation of this dispersion was achieved through manual injection into aqueous solutions of xanthan gum. The limitations of this method are highlighted by very low ultimate tensile strengths of these fibres, in the order of 3 MPa, with high variation within all of the fibres. Fibres were also produced via scrolling of bi-component films containing poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and poly(vinyl alcohol) (PVA). Chemical treatments were employed to impart water compatibility to these fibres, and their electrochemical, physical and electrical properties were analysed.
Fibres were wet spun from two PEDOT:PSS sources, in several fibre diameters. The effect of chemical treatments on the fibres were investigated and compared. Short 5 min treatment times with dimethyl sulfoxide (DMSO) on 20 ¼m fibres produced from Clevios PH1000 were found to produce the best overall treatment. Up to a six-fold increase in electrical conductivity resulted, reaching 800 S cm-1, with up to 40 % increase in specific capacitance and no loss of mechanical strength (55 F g-1 and 150 MPa recorded).
A wet spinning system to produce PEDOT:PSS fibres containing functionalised graphenes and carbon nanotubes, as well as birnessite nanotubes was subsequently developed. Manganese dioxide was also grown electrochemically on the outside of PEDOT:PSS fibres, with polypyrrole and PEDOT:PSS coating protection methods investigated. Electrochemical testing determined that birnessite nanotube-containing fibres presented the most viable option for energy storage device applications. Using the birnessite nanotube-containing fibre, fibre-based supercapacitors were fabricated and investigated. Specific capacitance values of 80 F g-1 were obtained, stable for over 1,000 cycles
Multilayered flexible fibers, consisting of carbon black-carbon nanotube fibers, manganese oxides and conducting polymers, were fabricated for use as electrodes in supercapacitors. Carbon-based fibers were initially prepared by wet-spinning using carbon-based nanomaterials (carbon black and carbon nanotubes) and chitosan as a matrix. Subsequent coatings with manganese oxides and conducting polymers form a multilayered structure. Different MnO2 crystalline structures (µ-MnO2, ³-MnO2) were grown onto the fibre by electrodeposition and different conducting polymers (polyethylenedioxythiophene and polypyrrole) used as a conductive wrapping. Each layer improved the performance of the fibre by adding different functionalities. While MnO2 improved the capacitance of the fibre, the presence of conducting polymers creates a conductive network increasing the capacitance further and conferring cycling stability. Capacitance values up 600 F g-1 and capacitance retention of 90% can be achieved with these multilayered hybrid fibers. A symmetric supercapacitor device, prepared from two hybrid fibres showed no significant change in properties when the device was bent, demonstrating their potential in flexible electronic devices and wearable energy systems.
Flexible microcomponents are being widely employed in the microelectronic industry; however; they suffer from a lack of complex movement. To address this problem, we have developed flexible, electrically conductive, magnetic composite fibres showing complex motion in three dimensions with the capacity to be selectively actuated. Flexible carbon-based fibres were prepared by wet-spinning and were subsequently modified by electrodepositing Co-Ni. The high aspect ratio of the fibre (40 ¼m diameter, 3.5 cm length) causes a directional dependence in the magnetostatic energy, which will allow for anisotropic actuation of the composite. Thus, the application of magnetic fields allows for a precise control of the movement with high reproducibility and accuracy.
Flexible fibre supercapacitors were fabricated by wet-spinning from carbon nanotube/carbon black dispersions, followed by straightforward surface treatments to sequentially deposit MnO2 and PEDOT:PSS to make ternary composite fibres. Dip coating the fibres after the initial wet-spinning coagulation creates a simple solution-based continuous process to produce fibre-based energy storage. Well-controlled depositions were achieved and have been optimised at each stage to yield the highest specific capacitance. A single ternary composite fibre exhibited a specific capacitance of 351/F/g?1. Two ternary composite fibre electrodes were assembled together in a parallel solid-state device, with polyvinyl alcohol/H3PO4 gel used as both an electrolyte and a separator. The assembled flexible device exhibited a high specific capacitance of 51.3/F/g?1 with excellent both charge-discharge cycling (84.2% capacitance retention after 1000/cycles) and deformation cycling stability (82.1% capacitance retention after 1000 bending cycles).
This study used Raman spectro-microscopy to investigate the synthesis and degradation of radiation-grafted anion-exchange membranes (RG-AEM) made using 50 ¼m thick poly(ethylene-co-tetrafluoroethylene) (ETFE) films, vinylbenzyl chloride (VBC) monomer, and 1-methylpyrrolidine (MPY) amination agent. The data obtained confirmed the operation of the grafting-front mechanism. VBC grafting times of 1 and 4 h led to low degrees of grafting homogeneity, while 72 h led to extreme levels of grafting that resulted in mechanically weak RG-AEMs due to the excessive H2O contents. A grafting time of 16 h was optimal yielding a RG-AEM with an ion-exchange capacity (IEC) of 2.06 ± 0.02 mmol g-1 (n = 3). An excess of grafting was detected at the surface of this RG-AEM (at least within the first few ¼m of the surface). This RG-AEM was then degraded in O2-purged aqueous KOH (1.0 mol dm-3) for 14 d at 80 °C. Degradation was detected throughout the RG-AEM cross-section, where the Raman data was quantitatively consistent with the loss of IEC. A slight excess of degradation was detected at the surface of the RG-AEM. Degradation involved the loss of whole benzyl-1-methypyrrolidinium grafted units as well as the direct attack on the pendent (cationic) pyrrolidinium groups by the hydroxide anions.
A miniaturized, flexible fiber-based lithium sensor was fabricated from low-cost cotton using a simple, repeatable dip-coating technique. This lithium sensor is highly suited for ready-to-use wearable applications and can be used directly without the preconditioning steps normally required with traditional ion-selective electrodes. The sensor has a stable, rapid and accurate response over a wide Li+ concentration range that spans over the clinically effective and the toxic concentration limits for lithium in human serum. The sensor is selective to Li+ in human plasma even in the presence of a high concentration of Na+ ions. This novel sensor concept represents a significant advance in wearable sensor technology which will target lithium drug monitoring from under the skin.
This paper outlines preliminary work developing graphene modified thermoplastic inserts to be used for the toughening of CFRP. The paper outlines laminate
manufacture, mechanical testing and fracture analysis of graphene modified CFRP.
Fibres made from different nanostructured carbons (carbon black (CB)), carbon nanotubes (CNT) and CB/CNT were successfully developed by wet-spinning. The variation of dispersion conditions (carbon nanomaterial concentration, dispersant/Carbon nanomaterial concentration ratio, CB/CNT concentration ratio, pH) resulted in different electrochemical performance for each type of fibres. Fibres with the best capacitance values (10 F g-1) and good cycling stability (89%) were obtained from fibres containing 10% carbon black and 90% carbon nanotubes. A solid-state supercapacitor was fabricated by assembling the CB/CNT fibres resulting in 9.2 F g-1 electrode capacitance. Incorporation of 0.2 wt.% birnessite-type potassium manganese oxide nanotubes dramatically increased the capacitance of the fibres up to 246 F g-1 due to the high specific capacitance of birnessite phase and the tubular nature of the nanomaterial.
The simple and effective approach of ?dipping and drying? cotton yarn in a dispersion of poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS) and multi-walled carbon nanotubes (MWCNT) resulted in the development of a highly conductive and flexible cotton fibres. Subsequent polyaniline (PANi) deposition yielded electrodes with significant biocompatible and antibacterial properties that could be fabricated (alongside quasi-reference electrodes) into solid-state wearable pH sensors, which achieve rapid, selective, and Nernstian responses (-61 ± 2 mV pH-1) over a wide pH range (2.0 ? 12.0), even in a pH-adjusted artificial sweat matrix. This development represents an important progression towards the realisation of real-time, on-body, wearable sensors.
Plasma processing, as a commercial and large-scale technology, was used to functionalize few-layer graphene (FLG) and multi-walled carbon nanotubes (MWCNT) in this work. The successful functionalities of FLG and MWCNT have been confirmed by elemental microanalysis, X-ray photoelectron spectroscopy, acid-base titration and zeta potential measurements. With the assistance of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT/PSS), a water-dispersible and conductive polymer, a composite of functionalized FLG and MWCNT was fabricated into large-size flexible films and also interdigitated microelectrodes for microsupercapacitor application via simple and scalable techniques (i.e. doctor blading and laser-etching). When normalised by volume and area, the device made from FLG(NH3)-MWCNT(Acid) (19.9 F cm-3 at 5 mV s-1 and 12.2 F cm-3 at 200 mV s-1) and FLG-MWCNT(Acid) (19.5 mF cm-2 at 5 mV s-1 and 12.8 mF cm-2 at 200 mV s-1) show the best performing composites, respectively, indicating how effective functionalization of FLG and MWCNT is for the enhancement of electrochemical capacitance. In-situ Raman microscopy confirmed the reversible pseudo-capacitive behaviour of electrode materials and the stable electrochemical performance of the devices. The facile techniques used in this work and the good device performance show their great potential for wearable applications.
Skin diseases are common in the UK, especially in children where 34% suffer from such diseases at some point. Wound care and management is also a significant burden to the UK healthcare system, estimated at an annual cost of £5.3 billion. Epidermal pH gives an indication of the physiological condition of the skin and the healing progress of wounds. An effective pH-sensing dermal patch would provide non-invasive skin and wound monitoring, aiding treatment. The aim of this work was to develop a fibre-based flexible electrode to measure skin/wound pH. This will facilitate point-of-care analysis and allow appropriate care to be administrated by medical professionals.
Highly conductive wet-spun poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) fibres, a prior concept developed by Reid et al., were adopted for pH analysis. With an optimised polyaniline (PANi) coating, these fibres displayed Nernstian responses (in a solid-state sensor containing a fabricated quasi-reference electrode) across a pH range of 3.0 to 9.0 when in contact with both pH-adjusted artificial sweat matrix and human plasma; the fibres had additional desirable antibacterial and biocompatible properties. To date, wet-spun PEDOT:PSS fibres have not been adopted in a chemical sensing capacity. This invention provides opportunities for future wearable, fibre-based sensors capable of real-time, on-body pH sensing (to monitor wound healing and skin disease). However, a primary limitation was poor tensile strength (32 ± 11 MPa), which could lead to fibre breakages in real-life wearable applications. To overcome this limitation, another substrate, modified electrically conductive cotton, was explored.
A simple and effective ?dipping and drying? approach involving cotton yarns in a dispersion of PEDOT:PSS and multi-walled carbon nanotubes (MWCNT) resulted in the development of a flexible, highly conductive cotton fibre. Subsequent PANi deposition yielded electrodes with significant biocompatible and antibacterial properties that could be fabricated (alongside quasi-reference electrodes) into a solid-state wearable pH sensor, which achieved rapid, selective, and Nernstian responses (-61 ± 2 mV pH-1) over a wide pH range (2.0 ? 12.0), even in pH-adjusted artificial sweat matrix and human plasma. To date, there is no prior published research that reports on this combination of conductive materials and cotton in such a sensing capacity. Furthermore, few previous reports have described conducting cotton threads with low enough electrical resistances to allow the electrodeposition of functional polymers, like PANi, whilst retaining the necessary flexibility for wearable applications. Thus, this development represents an important progression towards the realisation of real-time, on-body, wearable sensors.
Flexible wearable chemical sensors are emerging tools which target diagnosis and monitoring of medical conditions. One of the potential applications of wearable chemical sensors is therapeutic drug monitoring for drugs that have narrow therapeutic range. The effective dose of these drugs is so close to the toxic dose that it requires frequent monitoring of drug plasma concentration during patient administration. One example of such drugs is lithium which is used to treat bipolar disorder and major depression. This thesis investigated the possibility of developing a fibre-based wearable chemical sensor for lithium drug monitoring.
A flexible cotton-based Li+ selective sensor and carbon-based reference electrode were fabricated to be incorporated in a wearable dermal patch for potential lithium drug monitoring in patient with bipolar disorder. Cotton fibres were converted to conductive cotton fibres by dipping in single-walled carbon nanotube ink until their resistance decreased to 500 &. Conductive cotton fibres were coated with a Li+ selective membrane solution via dip-coating to fabricate the Li+ sensor. Carbon fibres were dip-coated in Ag/AgCl ink followed by a reference membrane solution to obtain the carbon-based reference electrode. Potentiometric measurements of the Li+ sensor and reference electrode were performed vs. a double junction reference electrode and vs. each other and comparable results were obtained. The potentiometric response of the cotton-based Li+ sensor was linear over the Li+ concentration range (0.1 ? 63 mM) for Li+ sensors which spans the ineffective, clinically relevant analytical range (0.4 ? 1.0 mM) and toxic range of Li+ serum concentration. These fibre-based sensors were capable of determining Li+ concentration in aqueous and plasma spiked samples.
An in vitro reverse iontophoresis experiment was performed to extract Li+ from under porcine skin by applying a current density of 0.4 mA cm-2 via two electrodes. Carbon fibre-based reverse iontophoresis electrodes were fabricated and used instead of conventional silver wire-based version and comparable results were obtained. The fibre-based Li+ sensor and reference electrodes were capable of determining the Li+ concentration in samples collected via reverse iontophoresis.
Furthermore, a pilot experiment was performed to determine the biocompatibility of the materials used to develop the fibre-based Li+ sensor and reference electrode with promising initial results.
This paper presents two different designs for frequency reconfigurable antennas capable of continuous tuning. The radiator, for both antenna designs, is a microstrip patch, formed from liquid metal, contained within a microfluidic channel structure. Both patch designs are aperture fed. The microfluidic channel structures are made from polydimethylsiloxane (PDMS). The microfluidic channel structure for the first design has a meander layout and incorporates rows of posts. The simulated antenna provides a frequency tuning range of approximately 118% (i.e. 4.36 GHz) over the frequency range from 1.51 GHz to 5.87 GHz. An experimental result for the fully filled case shows a resonance at 1.49 GHz (1.3% error compared with the simulation). Experienced rheological behavior of the liquid metal necessitates microfluidic channel modifications. For that reason, we modified the channel structure used to realise the radiating patch for the second design. Straight channels are implemented in the second microfluidic device. According to simulation the design yields a frequency tuning range of about 77% (i.e. 3.28 GHz) from 2.62 GHz to 5.90 GHz.
There is a growing desire for wearable sensors in health applications. Fibers are inherently flexible and as such can be used as the electrodes of flexible sensors. Fiber-based electrodes are an ideal format to allow incorporation into fabrics and clothing and for use in wearable devices. Electrically conducting fibers were produced from a dispersion of poly (3,4-ethylenedioxythiophene)-poly (styrenesulfonate) (PEDOT: PSS). Fibers were wet spun from two PEDOT: PSS sources, in three fiber diameters. The effect of three different chemical treatments on the fibers were investigated and compared. Short 5 min treatment times with dimethyl sulfoxide (DMSO) on 20 ¼m fibers produced from Clevios PH1000 were found to produce the best overall treatment. Up to a six-fold increase in electrical conductivity was achieved, reaching 800 S cm?1, with no loss of mechanical strength (150 MPa). With a pH-sensitive polyaniline coating, these fibers displayed a Nernstian response across a pH range of 3.0 to 7.0, which covers the physiologically critical pH range for skin. These results provide opportunities for future wearable, fiber-based sensors including real-time, on-body pH sensing to monitor skin disease.
Flexible wearable chemical sensors are emerging tools which target diagnosis and monitoring of medical conditions. One of the potential applications of wearable chemical sensors is therapeutic drug monitoring for drugs that have a narrow therapeutic range such as lithium. We have investigated the possibility of developing a fibre-based device for non-invasive lithium drug monitoring in interstitial fluid. A flexible cotton-based lithium sensor was coupled with a carbon fibre-based reference electrode to obtain a potentiometric device. In vitro reverse iontophoresis experiments were performed to extract Li+ from under porcine skin by applying a current density of 0.4 mA cm-2 via two electrodes. Carbon fibre-based reverse iontophoresis electrodes were fabricated and used instead of a conventional silver wire-based version and comparable results were obtained. The fibre-based Li+ sensor and reference electrodes were capable of determining the Li+ concentration in samples collected via reverse iontophoresis and the results compared well to those obtained by ion chromatography. Additionally, biocompatibility of the used materials have been tested. Promising results were obtained which confirm the possibility of monitoring lithium in interstitial fluid using a wearable sensor.
Alqurashi Khaled, Kelly James R., Wang Zhengpeng, Crean Carol, Mittra Raj, Khalily Mohsen, Gao Yue (2020) Liquid Metal Bandwidth-Reconfigurable Antenna, IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS 19 (1) pp. 218-222
Institute of Electrical and Electronics Engineers
This letter shows how slugs of liquid metal can be used to connect/disconnect large areas of metalization and achieve a radiation performance not possible by using conventional switches. The proposed antenna can switch its operating bandwidth between ultrawideband and narrowband by connecting/disconnecting the ground plane for the feedline from that of the radiator. This could be achieved by using conventional semiconductor switches. However, such switches provide point-like contacts. Consequently, there are gaps in electrical contact between the switches. Surface currents, flowing around these gaps, lead to significant back radiation. In this letter, the slugs of a liquid metal are used to completely fill the gaps. This significantly reduces the back radiation, increases the bore-sight gain, and produces a pattern identical to that of a conventional microstrip patch antenna. Specifically, the realized gain and total efficiency are increased by 2 dBi and 24%, respectively. The antenna has potential applications in wireless systems employing cognitive radio (CR) and spectrum aggregation.
The plasma treatment of few-layer graphene (FLG) was investigated for the effect on the performance in supercapacitors and microsupercapacitors. Modifications to the FLG surfaces were proven by comprehensive studies using characterisation techniques including elemental microanalysis, X-ray photoelectron spectroscopy, potentiometric titration, zeta-potential measurements and dispersion stability analysis.
A thermal pre-treatment to yield dried FLG was shown to increase the FLG surface charge and density due to the removal of adsorbed water and incorporation of carboxyl and phenolic functional groups. The thermal treatment was used before all characterisation methods were applied. An Ar gas plasma treatment on dried FLG was shown to introduce carboxyl and phenolic surface functional groups and reduce material variability. With increasing treatment time of Ar plasma, the FLG oxygen content increased by 1 at% due to the presence of a larger number of carboxyl functional groups.
The introduction of H2 gas at 3 wt% in Ar gas plasma produced a different functionalised FLG with a smaller quantity of carboxyl groups. Compared to the Ar gas plasma treated material, the H2/Ar gas treated material had a lower surface charge and density. NH3 gas plasma increased the nitrogen content of the FLG starting material two-fold according to XPS and elemental microanalysis. A multi-step treatment consisting of H2/Ar mixed gas plasma followed by NH3 gas plasma gave a further surface increase in nitrogen content by five times relative to the starting material.
Electrode films were manufactured using polytetrafluoroethylene (PTFE) and styrene-butadiene rubber (SBR) as non-conductive binders and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT/PSS) as a conductive binder. The electrode films were constructed into supercapacitors and microsupercapacitors. External testing with PTFE binder showed promise for the H2/Ar mixed gas plasma treated material with a specific capacitance of 195 F g-1 at 1 mA cm-2 in sulfuric acid electrolyte, a 50% increase relative to untreated FLG devices. The other treated materials did not match this performance because they did not contain low concentrations of oxygen surface functional groups and had large quantities of sp3 hybridised carbon atoms. The supercapacitor devices were studied with sulfuric acid and potassium hydroxide aqueous electrolytes. The devices with potassium hydroxide electrolyte did not match the performance of the materials in sulfuric acid electrolyte due to materials? incompatibilities.
Supercapacitor testing was additionally carried out with SBR and carboxymethyl cellulose (CMC) in sandwiched devices alongside potassium hydroxide and sulfuric acid electrolytes. The manufacture of the electrode films required 20 wt% of SBR-CMC binder. The electrochemical results were indistinguishable and had large resistances.
An extensive investigation into the manufacture of flexible electrode films with FLG, multi-walled carbon nanotubes (MWCNT) and PEDOT/PSS in composite electrode materials was carried out. The electrode films were laser-etched into interdigitated patterns for planar micro-supercapacitor devices with the application of polyvinylalcohol-phosphoric acid gel electrolyte. These devices performed best with a mass ratio of 1:3:1 (PEDOT/PSS:FLG:MWCNT), and with NH3 functionalised FLG and acid functionalised MWCNT. Gravimetric capacitances of 120 F g-1 at 5 mV s-1 and volumetric capacitances of 20 F cm-3 at 5 mV s-1 were obtained for the NH3:MWCNT(Acid) combination during long cycling tests (10,000 cycles) and showed capacity retentions > 80%. In-situ Raman microscopy analysis suggested that the PEDOT/PSS component underwent pseudo-capacitive, reversible changes during cycling tests but the dominant electric-double layer capacitive-like response was due to the FLG and MWCNT materials, which were highly stable.