Journal
APPLIED SURFACE SCIENCE
Volume 257, Issue 9, Pages 4038-4043Publisher
ELSEVIER
DOI: 10.1016/j.apsusc.2010.11.171
Keywords
SAMs; Thiols; Exchange; Contact angle; ToF-SIMS; Gold
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A process of chemical differentiation of neighboring Au features on a substrate (for biosensing applications) involves a step, where after electrochemical removal of a self-assembled monolayer (SAM) from one feature, another SAM is deposited onto it by incubation with a different thiol. During this incubation step, other undesorbed features are also exposed to this thiol which may lead to a partial SAM-thiol exhange, the extent of which is a function of time. Here, such surface reactions were followed on polystalline Au in both directions using contact angle measurements and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The thiols involved were dodecanethiol (DDT) which forms SAM promoting adsorption of proteins and 11-mercaptoundecyl)tri(ethylene glycol) (TPEG) whose SAM prevents such adsorption. The surface reactions in both directions cannot be described by a simple pseudo-first-order kinetics. It was found that while the DDT SAM interaction with a TPEG solution leads eventually to a total replacement, the reverse process, TPEG SAM interaction with DDT, leads to no noticeable exchange over the first 3 h and then asymptotically approaches similar to 50% replacement. (C) 2010 Elsevier B. V. All rights reserved.
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