Measuring and controlling the local environment of surface bound DNA in self assembled monolayers on gold when prepared using potential-assisted deposition.
2020
DNA self-assembled
monolayers (SAMs) were prepared using potential-assisted
deposition on clean gold single-crystal bead electrodes under a number
of conditions (constant or square-wave potential perturbations in
TRIS or phosphate immobilization buffers with and without Cl–). The local environment around the fluorophore-labeled DNA tethered
to the electrode surface was characterized using in situ fluorescence
microscopy during electrochemical measurements as a function of the
underlying surface crystallography. Potential-assisted deposition
from a TRIS buffer containing Cl– created DNA SAMs
that were uniformly distributed on the surface with little preference
to the underlying crystallography. A constant (+0.4 V/SCE) or a square-wave
potential perturbation (+0.4 to −0.3 V/SCE, 50 Hz) resulted
in similar DNA-modified surfaces in TRIS immobilization buffer. Deposition
using a square-wave potential without Cl– resulted
in lower DNA surface coverage. Despite this, the local environment
around the DNA in the SAM appears to be densely packed. This implies
the formation of clusters of densely packed DNA in the SAM. This effect
was also demonstrated when depositing from a phosphate buffer. DNA
clusters were significantly reduced when Cl– was
present in the buffer. Clusters were most prevalent on the low-index
plane surfaces (e.g., {111} and {100}) and less on the higher-index
planes (e.g., {210} or {311}). A mechanism is proposed to rationalize
the formation of DNA-clustered regions for deposition using a square-wave
potential perturbation. The conditions for creating clusters of DNA
in a SAM or for preventing these clusters from forming provide an
approach for tailoring the surfaces used for biosensing.
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