Browsing by Author "Higson, Seamus P. J."
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Item Open Access Current trends in explosive detection techniques(Elsevier Science B.V., Amsterdam., 2012-01-15T00:00:00Z) Caygill, J. S.; Davis, Frank; Higson, Seamus P. J.The detection of explosives and explosive-related compounds has become a heightened priority in recent years for homeland security and counter-terrorism applications. There has been a huge increase in research within this area- through both the development of new, innovative detection approaches and the improvement of existing techniques. Developments for miniaturisation, portability, field-ruggedisation and improvements in stand-off distances, selectivity and sensitivity have been necessary to develop and improve techniques. This review provides a consolidation of information relating to recent advances in explosive detection techniques without being limited to one specific research area or explosive type. The focus of this review will be towards advances in the last 5 years, with the reader being referred to earlier reviews where appropriate.Item Open Access Development of a flexible biosensor for the monitoring of lactate in human sweat for its medical use in pressure ischemia(Cranfield University, 2014-11) Tur García, Eva; Higson, Seamus P. J.Pressure ischemia is a medical condition characterised by the necrosis of the skin and underlying tissues in body areas exposed to prolonged pressure. This condition leads to the development of bedsores and affects 9% of hospitalised patients, costing the NHS between £1.4 and £2.1 billion per year. The severity of pressure ischemia has been linked to the concentration of sweat lactate, a product of sweat gland metabolism under anaerobic conditions, such as hypoxia. Normal levels of lactate in human sweat are 20±7 mM, but under ischemic conditions these can rise up to approximately 70 mM. This project presents the development of a novel flexible electrochemical enzyme-based biosensor for the continuous and non-invasive monitoring of sweat lactate with the potential for becoming a body-worn device for the early detection of pressure ischemia onset. The core of the recognition system is a flexible laminate, comprising two highly porous polycarbonate membranes, which provide support for the lactate oxidase enzyme, immobilised via covalent cross-linking. Oxidation of lactate produces H2O2, which is subsequently determined electrochemically. The transducer comprises a two-electrode system on a single flexible polycarbonate membrane, sputter-coated with gold (CE/RE) and platinum (WE) to render it conductive. The developed design has been improved through investigation into different factors regarding the immobilisation method of the enzyme in the laminate and the lowering of interferences from oxidising compounds present in sweat. The sensing system exhibits lactate selectivity at physiologically relevant concentrations in sweat for pressure ischemia (0–70 mM), with good reproducibility (7.2–12.2% RSD) for a hand-manufactured device. The reliability of the sensor’s performance and the capability to detect lactate fluctuations on human sweat samples has been demonstrated. The sensing system showed excellent operational and mechanical stability. The application of Nafion® on the WE lowered interferences from ascorbic acid and uric acid by 96.7 and 81.7% respectively. These results show promise towards the further development of a body-‐worn monitoring device for determining lactate levels in undiluted human sweat samples in a reproducible, fast and accurate manner.Item Open Access Electrochemical detection of TNT at cobalt phthalocyanine mediated screen-printed electrodes and application to detection of airborne vapours(Wiley-Blackwell, 2013-10-11) Caygill, J. S.; Collyer, Stuart D.; Holmes, Joanne L.; Davis, Frank; Higson, Seamus P. J.We describe the use of cobalt phthalocyanine as a mediator to improve the sensitivity for the electrochemical detection of TNT. Commercial screen-printed electrodes containing cobalt phthalocyanine were employed for determination of TNT. Improved sensitivities compared to screen-printed carbon electrodes without phthalocyanine were observed, current response for cyclic voltammetric measurements at modified electrodes being at least double that of unmodified electrodes. A synergistic effect between oxygen and TNT reduction was also observed. Correlation between TNT concentrations and sensor output was observed between 0–200 µM TNT. Initial proof-of-concept experiments combining electrochemical determinations, with the use of an air-sampling cyclone, are also reported.Item Open Access Labeless Immunosensor Assay for Fluoroquinolone Antibiotics Based Upon an AC Impedance Protocol.(Taylor & Francis, 2007-01-01T00:00:00Z) Garifallou, Goulielmos-Zois; Tsekenis, Georgios; Davis, Frank; Higson, Seamus P. J.; Millner, Paul A.; Pinacho, Daniel G.; Sanchez-Baeza, Francisco; Marco, M-Pilar; Gibson, Timothy D.This paper describes the construction of a labeless immunosensor for the antibiotic ciprofloxacin and its interrogation using an AC impedance protocol. Commercial screen-printed carbon electrodes were used as the basis for the sensor. Polyaniline was electrodeposited onto the sensors and then utilized to immobilize a biotinylated antibody for ciprofloxacin using classical avidin- biotin interactions. Electrodes containing the antibodies were exposed to solutions of antigen and interrogated using an AC impedance protocol. The faradaic component of the impedance of the electrodes was found to increase with increasing concentration of antigen. Control samples containing a non-specific IgG antibody were also studied and calibration curves obtained by subtraction of the responses for specific and non-specific antibody-based sensors, thereby eliminating the effects of non-specific adsorption of antigen.Item Open Access Long period grating based toluene sensor for use with water contamination(Elsevier Science B.V., Amsterdam., 2014-11-01T00:00:00Z) Partridge, Matthew; Wong, Rebecca; James, Stephen W.; Davis, Frank; Higson, Seamus P. J.; Tatam, Ralph P.A demonstration of the use of a calix[4]resorcinarene coated optical fibre long period grating sensor for the detection of toluene in water is presented. Monitoring water quality both for domestic use and around industrial sites is critical to the preservation of clean water provision. Here we show that, by using a fibre optic based sensor system, water quality monitoring can be carried out without the requirement for water sampling or pre-concentration. The results presented demonstrate that this proof-of-concept sensor is capable of sensing ∼100ppm concentrations of toluene with semi-selectivity and low (<10ppm) variation.Item Open Access Modifying monolayer behaviour by incorporating subphase additives and improving Langmuir–Blodgett thin film deposition on optical fibres(Elsevier, 2014-01-17) Partridge, Matthew; Wong, Rebecca; Collins, Mike; James, Stephen W.; Davis, Frank; Tatam, Ralph P.; Higson, Seamus P. J.Experiments showing the possibility of modifying the behaviour of calix[4]resorcinarene monolayers at the air–water interface and optimising the deposition of multilayer coatings onto optical fibres are presented. The nature of the subphase is fundamental to the behaviour of monolayers and their utility in coating and sensing applications. Here we show initial studies exploring the modification of the calix[4]resorcinarene monolayer–water interaction through the introduction of dipole altering alcohol additives to the aqueous subphase. We explored the effect of this modification for three small alcohols. The resulting isotherms of the materials showed a reduction in the surface pressure and area per molecule required in order for the monolayer to reach its point of collapse. Incorporation of alcohols shifted the point of collapse, leading to the application of ethanol being successful in improving the transfer of material via Langmuir–Blodgett coating onto optical fibres at lower pressures. This method may prove useful in allowing greater control over future sensor surface coatings.Item Open Access Optical and AFM study of electrostatically assembled films of CdS and ZnS colloid nanoparticles.(Elsevier Science B.V., Amsterdam., 2008-05-30T00:00:00Z) Suryajaya, S.; Nabok, Alexei; Davis, Frank; Hassan, A.; Higson, Seamus P. J.; Evans-Freeman, J.CdS and ZnS semiconducting colloid nanoparticles coated with the organic shell, containing either SO3− or NH2+ groups, were prepared using the aqueous phase synthesis. The multilayer films of CdS (or ZnS) were deposited onto glass, quartz and silicon substrates using the technique of electrostatic self- assembly. The films produced were characterized with UV–vis spectroscopy, spectroscopic ellipsometry and atomic force microscopy. A substantial blue shift of the main absorption band with respect to the bulk materials was found for both CdS and ZnS films. The Efros equation in the effective mass approximation (EMA) theoretical model allowed the evaluation of the nanoparticle radius of 1.8 nm, which corresponds well to the ellipsometry results. AFM shows the formation of larger aggregates of nanoparticles on solid surfaItem Open Access Optical fibre long period grating based selective vapour sensing of volatile organic compounds(Elsevier Science B.V., Amsterdam., 2010-01-07T00:00:00Z) Topliss, Stephen M.; James, Stephen W.; Davis, Frank; Higson, Seamus P. J.; Tatam, Ralph P.The chemical sensing capabilities of an optical fibre long period grating (LPG) coated with a functional material are explored. The LPG period and coating thickness are chosen such that the mode transition region, characteristic of LPGs coated with nanostructured coatings, corresponds with the phase matching turning point, ensuring optimum sensitivity. The functional material is a calixarene, which is shown to exhibit sensitivity to the aromatic compounds toluene and benzene, while being relatively insensitive to the aliphatic hydrocarbon hexane. A nanoscale cavity in the calixarene molecule entraps the VOC molecule, thereby altering the refractive index of the coating and influencing the transmission spectrum of the LPG. A sensitivity to toluene of 231 ppmv has been achieved, based on a spectrometer resolution of 0.3 nm. This is a weak molecular interaction thereby ensuring the sensor gives a reversible response when the VOC is removed. The recovery time is of the order of 15 s.Item Open Access Scanning electrochemical microscopy for the interrogation of biologically modified surfaces(Cranfield University, 2007-01) Roberts, William St John; Higson, Seamus P. J.; Johnson, G.; Lonsdale, D.; Griffiths, J.; Smart, PalieThis thesis describes two novel applications of scanning electrochemical microscopy (SECM) to biological systems. The first involves the characterisation of a novel, impedance based genomic DNA biosensor - previously developed within the group. SECM in feedback mode was used to interrogate a DNA-polyelectrolyte film to determine whether the changes observed by impedance were detectable by SECM. Using the SECM micropositioning device to pattern a carbon ink substrate, a dotted array of polyethylenimine (PEI) and single stranded DNA (ssDNA) was fabricated. Using hexamine ruthenium chloride as the redox couple, the array was then interrogated by a SECM area scan before and following exposure to complementary and non-complementary DNA. Upon the exposure of the DNA/PEI array to complementary DNA, the feedback current over the functionalised region was observed to increase, whereas on exposure of the array to non-complementary DNA, an increase in feedback current was also observed - but to a lesser degree. The second SECM application described involves the use of SECM to detect protein expression in cells. Using an established immunochemical protocol, the transmembrane protein, CD44, expressed by cultured RT112 cells was labelled via a primary/secondary antibody complex to horseradish peroxidase. Using hydrogen peroxide and hydroquinone, the activity of the HRP label was subsequently detected by SECM in feedback mode. The microelectrode tip was biased at a potential of -0.4V, a potential sufficient for the reduction of benzoquinone - the redox active product of the HRP catalysed reaction. The work presented represents the first application of SECM to detecting protein expression in cells and effectively demonstrates the promise this technique holds for immunochemical applications. An analysis of Uniscan’s innovation network is also presented, which provides a valuable insight into the management of such resources and how they may be orchestrated to extract maximal innovative value for all parties involved in a collaborative relationship.Item Open Access Scanning electrochemical microscopy for the characterisation of surfaces modified with biological molecules(Cranfield University, 2011-02) Holmes, Joanne L.; Higson, Seamus P. J.This thesis describes a novel fabrication procedure for microelectrodes to be used with the scanning electrochemical microscope (SECM), the characterisation of a variety of novel impedance based immunosensors, and the characterisation of a novel oligonucleotide biosensor. The thesis firstly describes the development of a protocol for the fabrication of reproducible microelectrodes characterised to identify suitability in use with the SECM. The thesis then describes the use of SECM in feedback mode to interrogate a variety of antibody-polyelectrolyte films determining whether the changes observed by impedance were detectable by SECM. A screen printed carbon ink surface was patterned with an array of biotinylated polyethyleneimine (PEI) which was exposed to Neutravidin and then the biotinylated antibody of interest. Using ferrocenecarboxylic acid as the redox couple, the array was interrogated by SECM, scanning before and following exposure to a series of concentrations of the complementary antigen and a non-complementary antigen. Upon the exposure of the PEI/Neutravidin/biotinylated antibody array to the antigen, the feedback current over the functionalised region was observed to change. The change observed increased as the concentration of the antigen exposed to the array was increased showing linear correlation. On exposure of the array to a non-complementary antigen, only a small change in the feedback current was observed. NSE, PSA, Ciprofloxacin and NTx were all investigated with limits of detection of 0.5 pg ml-1, 1 pg ml-1, 0.1 ng ml-1 and 1 nM respectively. Finally using a similar method as employed above, SECM was utilised in the detection of binding events of short oligonucleotides. Once again scans were conducted before and after exposure to both complementary and non-complementary oligonucleotide sequences and by subtraction absolute changes in feedback current were determined. On exposure to the complementary oligonucleotide sequence a change in feedback was observed when the array was exposed to the non-complementary oligonucleotide sequence, as with the antibody/antigen array, only a small change in the feedback current was observed.Item Open Access Sonochemically fabricated microelectrode arrays for biosensors. Part II. Modification with a polysiloxane coating(Elsevier Science B.V., Amsterdam., 2004-09-15T00:00:00Z) Myler, Suzy; Davis, Frank; Collyer, Stuart D.; Higson, Seamus P. J.A polymer modified sonochemically fabricated glucose oxidase microelectrode array with microelectrode population densities of up to 2.5 x 105 microelectrodes cm-2 is reported. These microelectrode sensors were formed by first depositing an insulating film on commercial screen printed electrodes which was subsequently sonicated to form cavities of regular sizes in the film. Electropolymerisation of aniline at the microelectrode cavities formed polyaniline protrusions containing entrapped glucose oxidase. Chemical deposition of polysiloxane from dichlorodimethysilane was used to deposit a thin protective and diffusion mass transport controlling coating over the electrodes. The physical and electrochemical properties of these films were studied. The performance of the final glucose oxidase based microelectrode sensor array is reported.Item Open Access Species differentiation by DNA-modified carbon electrodes using an ac impedimetric approach.(Elsevier Science B.V., Amsterdam., 2005-02-15T00:00:00Z) Davis, Frank; Nabok, Alexei; Higson, Seamus P. J.A simple and novel electrochemical biosensor based approach is described for differentiating between differing species of fish on the basis of DNA hybridisation events. Screen-printed carbon electrodes modified with a variety of polymers were used to immobilise commercially available DNA in a single- stranded form. AC impedimetric measurements were firstly carried out on these systems and then upon exposure to single-stranded DNA solutions. When the electrode and solution DNA were complementary, a large drop in impedance was measured; this did not occur for non-matching DNA exposures. DNA hybridisation sensors for closely related species of fish were in the first instance developed as a demonstration for this approach. Species of fish such as herrings and salmon could be differentiated by this method. This sensor format offers great promise for many DNA hybridisation applications and lends itself to mass fabrication due to the simplicity and inexpensiveness of the materials and methods used. The hybridisation results were confirmed by use of ellipsometry to measure the characteristics of similar films deposited on silicon substrates.Item Open Access Studies towards the development of label-free AC impedimetric immunosensors for healthcare and food quality control(Cranfield University, 2008-03) Tsekenis, Georgios; Higson, Seamus P. J.This thesis describes work focused towards the fabrication and characterisation of immunosensor platforms for the label-free detection of analytes of importance in the health and food industries. Due to their low unit cost and ease of fabrication, the immunosensor market has significantly increased recently, resulting in a constant demand for new immunosensor applications. Within this thesis, therefore, a novel fabrication protocol is reported towards the production of immunosensor platforms for the detection of the antibiotic, ciprofloxacin, the stroke and multiple sclerosis marker, Myelin Basic Protein (MBP) and the ovarian cancer marker CA-125. Initial investigations were aimed towards the electrochemical characterization of the available electrode substrates at the onset of this research project namely, gold sputter coated, screen-printed gold and carbon electrodes. They showed that only carbon electrodes provide sufficiently reproducible results and thus these electrodes have been employed for immunosensor fabrication. Due to the advantages of microelectrodes over planar electrodes, attempts to fabricate microelectrode arrays were also made via the ultrasonic ablation of passivated electrode assemblies. For the site-specific immobilisation of antibodies on polymer modified surfaces biotin-neutravidin affinity technologies were used. The fabricated immunosensors were then interrogated upon exposure to antigen solutions utilising the technique of electrochemical impedance spectroscopy (EIS). Changes in the obtained impedance spectra were used to plot calibration profiles for the detection of ciprofloxacin in buffer and in milk. Similar profiles have been plotted for Myelin Basic Protein (MBP) and the ovarian cancer marker CA-125.Item Open Access Ultra-Sensitive determination of pesticides via cholinesterase-based sensors for environmental analysis.(Elsevier, 2007) Davis, Frank; Law, Karen A.; Chaniotakis, Nikos A.; Fournier, Didier; Gibson, Timothy D.; Millner, Paul A.; Marty, Jean-Louis; Sheehan, Michelle A.; Ogurtsov, Vladimir I.; Johnson, Graham; Griffiths, John; Turner, Anthony P. F.; Higson, Seamus P. J.This review is focussed towards the development of acetylcholinesterase enzymatic based biosensors for the quantification of trace concentrations of highly toxic pesticides via their inhibitory effect on the enzyme. Initial results were obtained using wild-type enzymes which have a broad spectrum of susceptibility to a variety of pesticides. The sensitivity and selectivity of the enzyme activity was improved by development and screening of a wide range of mutant enzymes. Optimal enzymes were then exploited within a range of sensor formats. A range of immobilisation techniques including adsorption based approaches, binding via proteins and entrapment within conducting polymers were all studied. The incorporation of stabilisers and co-factors were utilised to optimise electrode performance and stability - with both planar and microelectrode geometries being developed. Reproducible quantification of pesticides could be obtained at concentrations down to 10-17 M, representing a detection limit hitherto unavailable.