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Biomedical subjects

Nicholas J Goddard

Publications and source records attributed to Nicholas J Goddard.

At least 19 recordsLinked to original sources
PubMed2007

Photochemistry of refractive index structures in poly(methyl methacrylate) by femtosecond laser irradiation.

Femtosecond, subablation threshold photomodification of poly(methyl methacrylate) (PMMA) at 387 nm is explored to enable fabrication of optical components. Volatile fragment analysis (thermal desorption gas chromatography-mass spectrometry) and molecular weight distribution monitoring (size exclusion chromatography) suggest photochemical modification, involving direct cleavage of the polymer backbone and propagation via chain unzipping under formation of monomers, similar to the pyrolytic degradation of PMMA. Waveguides were produced in undoped, clinical-grade PMMA, showing an increased refractive index in the laser focal region (Dnmax=4x10(-3)).

Journal Article↗
PubMed2006

Miniaturised isotachophoresis analysis.

The application of miniaturized total analysis systems (microTAS) has seen rapid development over the past few years. Isotachophoresis (ITP) has been transferred into microchip format for both electrophoretic separation and pretreatment purposes, due to its advantageous features including separation parameters controlled by electrolyte composition and high sample load capacity. The primary focus of this concise review is to summarize the basic features of microchip based ITP and its applications to the analysis and pretreatment of ionic compounds and biomolecules that have arisen since 1998.

DNA↗
PubMed2006

A micro-reactor for preparing uniform molecularly imprinted polymer beads.

In this study, uniform spherical molecularly imprinted polymer beads were prepared via controlled suspension polymerization in a spiral-shaped microchannel using mineral oil and perfluorocarbon liquid as continuous phases. Monodisperse droplets containing the monomers, template, initiator, and porogenic solvent were introduced into the microchannel, and particles of uniform size were produced by subsequent UV polymerization, quickly and without wasting polymer materials. The droplet/particle size was varied by changing the flow conditions in the microfluidic device. The diameter of the resulting products typically had a coefficient of variation (CV) below 2%. The specific binding sites that were created during the imprinting process were analysed via radioligand binding analysis. The molecularly imprinted microspheres produced in the liquid perfluorocarbon continuous phase had a higher binding capacity compared with the particles produced in the mineral oil continuous phase, though it should be noted that the aim of this study was not to optimize or maximize imprinting performance, but rather to demonstrate broad applicability and compatibility with known MIP production methods. The successful imprinting against a model compound using two very different continuous phases (one requiring a surfactant to stabilize the droplets the other not) demonstrates the generality of this current simple approach.

Equipment Design↗
PubMed2005

Rapid chloride analysis using miniaturised isotachophoresis.

A new design of miniaturised separation device for performing isotachophoresis (ITP) has been produced. The device contains a simple arrangement of channels comprising a single separation channel with a 'double T' injection geometry. The device was produced in poly(methyl methacrylate) and incorporates an on-column conductivity detector. A new electrolyte system was developed to enable the rapid determination of chloride to be made. This electrolyte system uses a leading ion of 3.5 mM nitrate at pH 3.0 with 0.5 mM indium(III) added as a complexing agent. Use of this electrolyte system with the new separation device allowed chloride samples to be analysed in under 100 s, with a limit of detection (LOD) calculated to be 2.2 mg l(-1).

Chlorides↗
PubMed2005

An integrated optical leaky waveguide sensor with electrically induced concentration system for the detection of bacteria.

An integrated, sensitive and rapid system was developed for the detection of bacteria. The system combined an optical metal-clad leaky waveguide (MCLW) sensor with an electric field. The electric field was used to concentrate Bacillus subtilis var. niger(BG) bacteria spores onto the immobilized anti-BG antibody on the MCLW sensor surface. This sensor combination has been characterised by detecting the scattering from bacterial spores, which are concentrated at the sensor surface, when they are illuminated at the coupling angle; and by detection of fluorescence from labelled antibodies added after the spores had been captured on the surface. The light scattering and fluorescence detection methods gave a detection limit of BG bacterial spores of 1 x 10(3) spores ml(-1) when the electric field was applied for 3 minutes.

Bacillus subtilis↗
PubMed2005

Optical leaky waveguide sensor for detection of bacteria with ultrasound attractor force.

An integrated, sensitive, and rapid system was developed for the detection of bacteria. The system combined an optical metal-clad leaky waveguide (MCLW) sensor with ultrasound standing waves (USW). The performance of a MCLW sensor for the detection of bacteria has been increased (>100 fold) by using USWs to drive bacteria onto the sensor surface. By forming the USW nodes at or within the surface of the MCLW, the diffusion-limited capture rate has been replaced by fast movement. Immobilized anti-BG antibody on the MCLW sensor surface was used to capture Bacillus subtilis var. niger (BG) bacterial spores driven to the surface. This combination of sensor and attractor force combination has been tested by detecting the evanescent scattering from bacterial spores at the sensor surface. Application of ultrasound for 3 min gave a detection limit for BG bacterial spores of 1 x 10(3) spores/mL.

Bacillus subtilis↗
PubMed2005

Analysis of chloride, bromide and iodide using miniaturised isotachophoresis on a planar polymer chip.

A new method has been developed to allow the determination of the halide anions chloride, bromide and iodide using isotachophoresis. This method employs a new electrolyte system which incorporates the novel application of indium(III) as a complexing agent. This electrolyte system was devised based on the findings of an investigation into the potential for using indium(III) as a complexing counter ion to selectively manipulate the effective mobilities of halide ions. A leading electrolyte incorporating 3.5 mmol dm(-3) of indium(III) allowed the simultaneous determination of chloride, bromide and iodide to be successfully achieved. The new procedure allows such separations to be made without interference from common inorganic anions such as sulfate and nitrate. Separations were performed using a miniaturised planar poly(methyl methacrylate) chip with integrated platinum wire conductivity detection electrodes. Using this instrumentation the limits of detection were calculated to be 0.7 mg dm(-3), 1.7 mg dm(-3) and 2.2 mg dm(-3) for chloride, bromide and iodide respectively.

Anions↗
PubMed2005

An integrated disposable dye clad leaky waveguide sensor for micro-TAS applications.

An integrated, disposable, dye clad leaky waveguide (DCLW) device has been fabricated and tested for both refractive index and fluorescence detection in mu-TAS applications. The chip comprises the required flow geometry and optical coupling elements in a robust device that is relatively simple and inexpensive to fabricate. Disposable DCLW chips were fabricated at room temperature by spin-coating both the dye and silica sol-gel waveguiding layers on a polymer substrate which contained injection moulded grating coupler. These devices have been designed to increase the interaction of the evanescent field light at the channel wall and with the sample in the channel. The DCLW device has been used to detect changes in the refractive index of different percentages of glycerol solutions and to detect low concentrations down to 10(-12) M fluorescein using a grating coupler.

Journal Article↗
PubMed2005

Metal clad leaky waveguides for chemical and biosensing applications.

Novel metal clad leaky waveguide (MCLW) sensor devices have been developed for sensing applications. These chips are designed to confine the light in a low refractive index waveguide that encompasses the chemically-selective layer, maximising the overlap between the optical mode and the chemistry, thus improving the sensitivity. In this work, a thin metal layer was inserted between the substrate and the thick waveguide layer, increasing the reflectivity of the waveguide/metal interface and decreasing the light lost at each of reflection in the leaky mode, which in turn increases the propagation distance. The device has been used for a range of biosensing applications, including the detection of organophosphoros pesticides. The limit of detection for paraoxon, based on absorbance detection, was calculated to be 6 nM. Refractive index detection was demonstrated by monitoring the change in the out-coupled angle resulting from the binding of protein A to anti-protein A immobilized on agarose. The sensor was also used for detecting the quenching of the fluorescence of an acid-base sensitive ruthenium complex immobilized within the sol-gel and with glucose oxidase enzyme. The limit of detection for glucose was 3 microM. The advantage of using the metal layer in the MCLW was that an electrical potential could be applied to accelerate the diffusion of the analyte to the immobilised antibody, which resulted in a shortened analysis time and a reduction in non-specific binding.

Biosensing Techniques↗
PubMed2005

An integrated metal clad leaky waveguide sensor for detection of bacteria.

An integrated optical metal clad leaky waveguide (MCLW) sensor device has been developed for the detection of bacteria. This is more sensitive than waveguide sensors currently in use. The MCLW device has been fabricated to extend the evanescent field to provide significant light intensity over the entire volume of the bacteria bound on the chip surface within this field. This in turn increases the interaction of the light with the entire volume of the bacteria. MCLW devices have been used for detecting refractive index changes, scattering, and fluorescence from bacterial spores captured on an immobilized antibody. The detection limit of Bacillus subtilis var. niger bacterial spores using refractive index detection was 8 x10(4) spores/mL. The scattering intensity of the BG spores was found to be three times greater than the scattering intensity generated using surface plasmon resonance. The extended light propagation along the direction of flow for a few millimeters provides an effective interrogation approach to increase the area of detection to detect low concentrations down to 1 x 10(4) spores/mL. The sensor was then optimized by studying the key factors affecting sensor performance including changing the pH of the medium, type of antibody immobilization matrix, sensor surface regeneration approaches, and longevity of the sensor.

Bacteria↗
PubMed2004

Bacteria detection using disposable optical leaky waveguide sensors.

Novel disposable absorbing material clad leaky waveguide sensor devices (LWD) have been developed for the detection of pathogenic particles such as bacteria. These chips are tailored to give the maximum extension of the evanescent field at the sensor surface in order to place the entire volume of the bacteria captured by immobilized antibodies on the chip surface within this field. This in turn increases the interaction of the light with the bacteria's bulk volume. Disposable LWD chips were fabricated at room temperature and without the use of expensive fabrication equipment. These LWDs have been characterised by detecting refractive index (RI) changes, scattering and fluorescence from bacterial spores at the sensor surface when illuminated at the coupling angle. The detection limit of Bacillus subtilis var. niger (BG) bacterial spores was 10(4) spores/ml and the illumination intensity of the spores was found to be three times greater than the illumination intensity generated using the surface plasmon resonance (SPR).

Bacillus↗
PubMed2004

Analysis of amino acids by miniaturised isotachophoresis.

A method allowing the miniaturised isotachophoretic analysis of amino acids has been developed. To overcome the problems of carbonate contamination which occur when performing separations at alkaline pH levels glycolate was used as the leading ion. Addition of magnesium to the leading electrolyte as a counter species was found to improve the separations. The method has been used on a poly(methyl methacrylate) microdevice with integrated on-column conductivity detectors. The behaviour of a range of common amino acids was investigated and successful separations of up to seven amino acids were made. Good linearity was observed with calibration curves for aspartic acid and phenylalanine over the range 0.063-1.0 mM. Limits of detection for these two species were calculated to be 0.060 and 0.018 mM, respectively.

Amino Acid Sequence↗
PubMed2004

Use of miniaturised isotachophoresis on a planar polymer chip to analyse transition metal ions in solutions from metal processing plants.

An electrolyte system, using malic acid as a complexing agent, has been developed to allow the determination of transition metal cations using miniaturised isotachophoresis. The method allowed the simultaneous determination of Mn2+, Cr3+, Fe2+, Co2+, Zn2+ and Ni2+ to be made without interference from other common ions. Limits of detection were calculated to be in the range 0.5-1.0mg l(-1) for Mn2+, Cr3+ Co2+ and Zn2+ and 2.0 mg l(-1) for Fe2+ and 4.7 mg l(-1) for Ni2+. The successful analysis of five industrial samples, containing a range of these metal ions, obtained from metal processing plants were achieved in under 13 min. The separations were performed on a poly(methyl methacrylate) chip with integrated platinum wire conductivity detection electrodes.

Electrophoresis↗
PubMed2003

A yeast-based cytotoxicity and genotoxicity assay for environmental monitoring using novel portable instrumentation.

An assay capable of simultaneously measuring both general toxicity and more subtle genotoxicity, in aqueous environmental samples, is described. The assay uses eukaryotic (yeast) cells, genetically modified to express a green fluorescent protein (GFP) whenever DNA damage, as a result of exposure to genotoxic agents, is repaired. A measure of the reduction in cell proliferation is used to characterise general toxicity producing familiar EC(50) and LOEC data. The assay protocol has been developed for proposed use in the field and hence employs dedicated, portable instrumentation, the development of which is described. A range of environmentally relevant substances has been evaluated using the assay, including solutions of metal ions, solvents and pesticides. Preliminary data comparing the yeast assay's response to that of a standard Daphnia test in the analysis of the toxicity of 34 varied industrial waste effluents are also presented. The sensitivity to a wide range of substances and effluents suggests the assay should be useful for environmental toxicity monitoring.

Animals↗
PubMed2003

Determination of inorganic selenium species by miniaturised isotachophoresis on a planar polymer chip.

The use of miniaturised isotachophoresis to allow the simultaneous determination of two inorganic selenium species has been investigated using a poly(methyl methacrylate) chip with a 44-mm-long, 200-microm-wide, 300-microm-deep separation channel. The miniaturised device included an integrated on-column, dual-electrode conductivity detector and was used in conjunction with a hydrodynamic fluid transport system. A simple electrolyte system has been developed which allowed the separation of selenium(IV) and selenium(VI) species to be made in under 210 s. The limits of detection were calculated to be 0.52 mg L(-1) for selenium(IV) and 0.65 mg L(-1 )for selenium(VI). The method allowed the separation of the selenium species from a range of common anions including fluoride, nitrate, nitrite, phosphate, sulfate and sulfite.

Journal Article↗
PubMed2003

Miniaturised isotachophoretic analysis of inorganic arsenic speciation using a planar polymer chip with integrated conductivity detection.

A new method allowing the analysis of inorganic arsenic species using isotachophoresis has been developed. This method has been shown to be suitable for use on both miniaturised planar polymer separation devices and capillary scale devices. A poly(methyl methacrylate) chip with integrated conductivity electrodes has been successfully used for the rapid analysis of inorganic arsenic species in under 600 s. Limits of detection of 1.8 mg l(-1) and 4.8 mg l(-1) for arsenic(V) and arsenic(II), respectively, have been achieved with the miniaturised device. The device has also been used to perform the simultaneous separation of arsenic(III), arsenic(V), antimony(III), molybdenum(VI) and tellurium(IV).

Electric Conductivity↗
PubMed2003

Determination of the ascorbate content of photographic developer solutions using miniaturised isotachophoresis on a planar chip.

The use of miniaturised isotachophoresis, performed on a planar poly(methyl methacrylate) device with integrated platinum conductivity electrodes, for the analysis of the ascorbate content of photographic developer solutions has been investigated. An electrolyte system has been developed which enabled the analysis to be made without interference from any of the other components in the developer solution, a number of which were present at significantly higher concentrations than that of the ascorbate ions. Using this system, the ascorbate content of the developer solutions could be analysed in under 6 min. The limit of detection for ascorbate using miniaturised isotachophoresis was calculated to be 0.011 mmol dm(-3).

Journal Article↗