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Electrodeposited DNA monolayers on gold : creation, evaluation and optimization Leung, Kaylyn Kyra


Deoxyribonucleic acid (DNA) self-assembled monolayers (SAMs) consist of bioelectronic interfaces that have been proposed for use as DNA biosensors. These are portable medical device used for diagnosing diseases through specific detection of biomolecules. These DNA SAMs are composed of chemically modified DNA molecules adsorbed onto gold surfaces and are made by immersing a gold surface in a solution of thiol-modified DNA. Previous literature has shown that an applied potential to the gold surface during the DNA immersion enhances DNA SAM formation by decreasing self-assembly time and forming DNA SAMs of higher quality. These electrodeposited DNA SAMs were observed using average measurement techniques on the entire surface. These averaged techniques are unable to characterize heterogeneous features in DNA SAMs. Instead, an imaging technique such as in-situ electrochemical fluorescence microscopy (iSEFMI) can be used to investigate these electrodeposited DNA SAMs. In this work, DNA SAMs were electrodeposited onto single crystal bead electrodes. These electrodes were key for examining DNA SAMs on different surface crystallographies (ie. surface atomic arrangements). Using iSEFMI, the electrodeposited DNA SAMs on the single crystal bead electrodes were characterized, with DNA coverage measurements on each surface crystallography possible. It was established that applying either negative or positive potentials resulted in DNA SAMs of high coverage with positive potentials resulting in more uniform DNA coverages across all surface crystallographies. Applying a modulating potential further created DNA SAMs of slightly higher DNA coverages. The effect of an applied potential on DNA SAMs adsorbing onto different surface crystallographies was also investigated. Both a constant potential and a modulating square wave potential will be applied and the resulting DNA SAMs studied. The presence of specifically adsorbing anions in solution was found to affect both the gold surface and the potential-assisted DNA deposition resulting in a DNA SAM of unusual character. Understanding the factors that affect potential-assisted DNA deposition will enable the formation of an optimal procedure for manufacturing DNA SAMs. With the appropriate variables controlled, DNA SAMs can be tailored for their application in DNA biosensors and eventual use in point-of-care devices.

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