Electrochemical surface enhanced Raman spectroscopy of a beacon probe immobilized on Au electrodes

Abstract

The aim of this thesis is to investigate the factors, and possible mechanisms, involved in the electrochemical SER response of a reporter dye attached to an immobilized oligonucleotide on the negatively charged Au surface. This work used a 5’-thiol anchored beacon and a partial self-pairing oligonucleotide, instead of a linear strand probe, to study the sensing process. The observation of the SERS intensity of the 3’-labelled dye at the negatively charged Au surface is similar to that of the hybridized duplex of the linear probe at low surface coverage.

By competitive adsorption of mercaptohexanol together with the beacon probe in the immobilization solution, 3 times lower coverage than reported previously was achieved to ensure low intramolecular interactions between the beacon probe. A number of electrochemical methods were also utilized to observe the Raman intensity of the Texas Red-labelled beacon probe and the results interpreted in terms of the configuration changes of the beacon probe.

The potential dependent Raman enhancement of the reporter itself, Texas Red, was later found to have a similar response to the labelled beacon probe. A detailed discussion with respect to absorption of the Texas Red, orientation, potential tuning of the LSPR, the interference from hydrogen evolution, the electronic Stark effect and the charge-transfer enhancement is presented, to understand the possible contributions to the potential dependence Raman enhancement. As a result, a molecule-to-metal charge-transfer mechanism was found to explain the most relevant dependence of the enhancement on electrode potential.

The potential dependent Raman response of the corresponding beacon probe was compared as a function of the time scale of the modification, the alkyl chain length of mercaptoalkanol from C2, C4, C6 and C9 and the preparation method used (backfilling or co-adsorption). The possible surface states are proposed to explain the electrochemical SERS response of the system.

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Identifiers

ORCID for Philip N. Bartlett: orcid.org/0000-0002-7300-6900

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