Unforeseen distance-dependent SERS spectroelectrochemistry from surface-tethered Nile Blue: the role of molecular orientation

Covalent immobilization of redox-active dyes is an important strategy to evaluate structure-activity relationships in nanoscale electrochemistry by using optical readouts such as surface-enhanced Raman scattering (SERS). Here we investigate the role of the tether length in the SERS spectroelectroche...

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Bibliographic Details
Published in:Analyst (London) 2016-08, Vol.141 (17), p.5144-5151
Main Authors: Wilson, Andrew J, Willets, Katherine A
Format: Article
Language:English
Subjects:
Carbon
Derivatives
Dyes
Electrodes
Nanostructure
Orientation
Raman scattering
Tethers
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Summary:Covalent immobilization of redox-active dyes is an important strategy to evaluate structure-activity relationships in nanoscale electrochemistry by using optical readouts such as surface-enhanced Raman scattering (SERS). Here we investigate the role of the tether length in the SERS spectroelectrochemistry of surface-attached Nile Blue. Differential pulse voltammetry and a potential-dependent SERS derivative analysis reveal that the Nile Blue molecules adopt a different orientation with respect to the electrode surface as the number of carbons in a carboxylic acid-terminated alkanethiol monolayer is varied, which leads to unique SERS spectroelectrochemical behaviors. We use the relative molecular orientations and spectral characteristics to propose a model in which tethers shorter than the length of the molecule limit molecular motion under electrochemical perturbation, but tethers longer than the length of the molecule allow dye intercalation into the hydrophobic self-assembled monolayer, producing an unexpected decrease in the SERS intensity when the molecule is in the oxidized form. The tether length of Nile Blue impacts molecular orientation leading to unique SERS spectroelectrochemistry.
ISSN:0003-2654
1364-5528
DOI:10.1039/c6an01266c