Scanning electrochemical microscopy for the interrogation of biologically modified surfaces

This 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.