The future development of a novel, rapid, highly specific and stable electrochemical biosensor for DNA and small molecule drug detection has been addressed in this report. The surface modification strategy employed was initially tested on anthraquinone modified diamond and glassy carbon electrodes via diazonium reduction chemistry, removal of the Boc protection group and subsequent solid-phases synthesis. Following the successful immobilisation, the surface density of anthraquinone is shown to be controllable through use of an inert linker molecule. Anthraquinone surface coverages are found to be greatest on the glassy carbon electrode, yet diamond electrodes reduce anthraquinone more readily with an optimum surface density in the region of 1 x 1012 molecules cm-2, as required for efficient DNA detection. The superiority of the diamond electrode was demonstrated by immobilisation of probe ssDNA using the same modification strategy with addition of the reactive group, maleimide, which stems from earlier work using the redox probe, 6-(ferrocenyl)hexanethiol. Following successful immobilisation, an attempt to control the surface density of probe ssDNA was performed using an inert spacer molecule, 6-mercaptohexanol. Even though optimum probe densities were not achieved, detection of target ssDNA on diamond was evidenced via successful intercalation of methylene blue between the π-stacks of the DNA duplex. The effect of pH on both anthraquinone and probe ssDNA modified electrodes were studied and confirmed that these systems can efficiently operate under non-physiological pH conditions. The long-term operational stability of 6-(ferrocenyl)hexanethiol immobilised diamond electrodes were examined and it was proven that this system has high stability to reductive desorption, compared with 6-(ferrocenyl)hexanethiol immobilised gold electrodes.
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