|Title||Tailoring the DNA SAM surface density on different surface crystallographic features using potential assisted thiol exchange|
|Publication Type||Journal Article|
|Year of Publication||2018|
|Authors||Leung, KK, Gaxiola, ADiaz, Yu, HZhong, Bizzotto, D|
Received 23 October 2017
Self-assembled monolayers Electrodeposition Thiol-exchange
Self-assembled monolayers(SAMs) of DNA on gold surfaces are used in the manufacturing of a variety of nucleic acid based bio- sensors (e.g., aptamer-based biosensors) [1e4]. They are conven- tionally made by exposing a clean gold surface to thiol-modified DNA molecules which chemisorb to the gold surface via a gold-thiol covalent interaction. In a consecutive step, non-specifically adsor- bed DNA, or DNA adsorbed to the gold surface via the nitrogenous bases, is displaced with exposure to a short chain alkylthiol [5,6]. Typically, this process takes place on a gold surface that is at the open circuit potential(OCP). However, the surface coverage and local environment around the DNA in a SAM are not easily
* Corresponding author. Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, BC V6T 1Z1, Canada.
E-mail address: (D. Bizzotto).
Bristol, Bristol, UK, BS8 1TL.
0013-4686/© 2017 Elsevier Ltd. All rights reserved.
The influence of surface crystallography and applied potential on the thiol-exchange procedure to create mixed alkylthiol DNA SAMs is detailed. A single crystal gold bead and fluorophore labeled thiol modified DNA were used to characterize the resulting surface modifications. The thiol-exchange occurs with different efficiencies on the low index planes (111,100,110) as compared to 311 and 210. Positive applied potentials (>0/SCE) result in 10 higher coverage than when compared to deposition at the open circuit potential (OCP) over the same 60 min time period. Negative potentials ( < 0/SCE) resulted in less uniform coverage with the 111 facet being significantly modified. The electrolyte used during the deposition was a 10 mM TRIS Buffer with 100 mM NaCl 500 mM MgCl2. The influence of [Cl] was studied showing it had a significant impact on the thiol-exchange at the positive potentials, where higher [Cl] resulted in higher DNA coverages and a more uniform coverage across the multi-crystalline surface. The local environment of the thiol-exchanged DNA SAMs were compared for different regions on the surface using potential driven DNA reorientation modulating the fluorescence intensity. These results showed a common behaviour from all surfaces suggesting that the DNA SAMs prepared by thiol-exchange were consistently prepared with a variable surface concentration controlled by potential and time.