Browsing by Author "Holmes, Joanne L."
Now showing 1 - 3 of 3
Results Per Page
Sort Options
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 A new application of scanning electrochemical microscopy for the label-free interrogation of antibody-antigen interactions.(Elsevier Science B.V., Amsterdam., 2011-03-18T00:00:00Z) Holmes, Joanne L.; Davis, Frank; Collyer, Stuart D.; Higson, Seamus P. J.Within this work we present a 'proof of principle' study for the use of scanning electrochemical microscopy (SECM) to detect and image biomolecular interactions in a label-free assay as a potential alternative to current fluorescence techniques. Screen-printed carbon electrodes were used as the substrate for the deposition of a dotted array, where the dots consist of biotinylated polyethyleneimine. These were then further derivatised, first with neutravidin and then with a biotinylated antibody to the protein neuron specific enolase (NSE). SECM using a ferrocene carboxylic acid mediator showed clear differences between the array and the surrounding unmodified carbon. Imaging of the arrays before and following exposure to various concentrations of the antigen showed clear evidence for specific binding of the NSE antigen to the antibody derivatised dots. Non-specific binding was quantified. Control experiments with other proteins showed only non-specific binding across the whole of the substrate, thereby confirming that specific binding does occur between the antibody and antigen at the surface of the dots. Binding of the antigen was accompanied by a measured increase in current response, which may be explained in terms of protein electrostatic interaction and hydrophobic interactions to the mediator, thereby increasing the localised mediator flux. A calibration curve was obtained between 500 fg mL(-1) to 200 pg mL(-1) NSE which demonstrated a logarithmic relationship between the current change upon binding and antigen concentration without the need for any labelling of the substrate.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.