ABSTRACT
As mentioned in the introduction section electrochemically commanded SAM-based surfaces are a very interesting platform for performing a variety of reactions in a selective way and in confined regions of surfaces that can be patterned by soft lithography [10]. To design these systems one should first consider the nature of the substrate and the SAM to be used for each particular case. SAMbased systems (devices) under electrochemical control for biological applications require the use of conducting, biocompatible substrates able to work in aqueous solutions at physiological pH values. Metallic substrates are particularly useful for this purpose because they can be polarized in a wide range of potentials within the stability window of water. Among metals we are interested in
those exhibiting extremely good stability in the working conditions, thus avoiding metal dissolution, oxide formation, and other faradaic processes such as hydrogen or oxygen evolution reactions among others. Gold is the best option because it satisfies all these requirements. Gold is chemically inert in ambient conditions, is easy to clean, and exhibits an extended double-layer region only limited by the HER from the cathodic side and gold oxide monolayer formation from the anodic side. Anion adsorption could take place in the double-layer region, although chemisorbed SAMs completely displace these species from the Au surface. Concerning the SAMs, molecules such as thiol, alkyldisulfides, and alkylsulfides have been widely used to form dense, well-ordered monolayers on gold [11]. Also, carbamates [12] and thiocyanates can form thiol SAMs on gold surfaces [13].
