The present invention is in the field of preparing self-assembled monolayers on a metal using electrolysis.
Molecular self-assembly of monolayers (SAMs) provides a simple method to form highly ordered two-dimensional organic assemblies. Among the various systems that display this behavior, SAMs formed by the chemisorption of alkanethiols on gold to produce strong gold-thiolate bonds is particularly convenient because of the ease of their preparation. [1-3] Well-ordered SAMs form spontaneously on gold surfaces within a short period upon immersion of the surface in either a dilute solution or the vapor of an alkanethiol of interest. These monolayers have been used as model systems for fundamental studies of wettability [4], adhesion [5], biocompatibility [6], fouling [7], as well as serving as the basis for building multilayers [8] and bio- and analytical sensors [9], for the immobilization of biomolecules [10], and for preparing patterned surfaces [11].
One of the most attractive characteristics of self-assembled monolayers (SAMs) is the facility of their preparationxe2x80x94simply exposing a substrate surface to an appropriate adsorbate-[1-3] though this facility prevents selective formation at particular surfaces in the presence of others of the same composition. While contact printing of SAMs has proven useful in preparing mesoscale patterns on various substrates [12], formation of monolayers on only particular features of a pre-existing patternxe2x80x94such as an electrode array, an integrated circuit, or a MEMS devicexe2x80x94has remained an elusive synthetic challenge. Hence, treating an array of identical gold electrodes with a solution of an alkanethiol or alkyl disulfide would result in formation of a monolayer on all of the electrodes. One approach to controlling self-assembly in these systems has focused on the inability of thiolate ions to covalently bind the gold surface directly, without concomitant oxidation. [13] Hence, gold electrodes immersed in a solution of thiolate ions will only adsorb a SAM if held at a sufficiently high potential. Electrochemistry, in this case reduction, can also be used to remove SAMs that had previously been adsorbed. [14] Hence, an alternative strategy for producing patterns involves allowing indiscriminate self-assembly to occur, followed by articulation of a pattern by the selective removal of the SAM from certain substrates.
Alkylthiosulfates, also known as Bunte salts, can be used to synthesize disulfides by oxidation [15], acidic hydrolysis [16-17], or alkaline degradation [18]. Disulfides also can be formed from Bunte salts electrochemically. [19-20] This method has been extended to form polydisulfides from xe2x80x9cdoublexe2x80x9d Bunte salts, molecules carrying two thiosulfate groups, using electrochemistry with gold electrodes. [21]
Disclosed is a method of preparing self-assembled monolayers on a metal comprising electrolyzing a thiosulfate compound in a solvent, where the electrolysis is performed at a voltage for a period of time.
Also disclosed is a method of preparing self-assembled organic monolayers on a metal comprising (a) contacting said metal with a solution comprising an organic thiosulfate compound, and (b) electrolyzing said organic thiosulfate compound by applying on said metal sufficiently high anodic potential for sufficient time to result in the oxidative self-assembly of said monolayers on said metal.
Further, a method is disclosed for the selective formation of self-assembled organic monolayers on a first metal electrode in the vicinity of a second metal electrode, comprising (a) contacting said metal electrodes with a solution comprising an organic thiosulfate compound under conditions such that chemisorption of said organic thiosulfate compound onto said first and second electrodes does not occur, and (b) electolyzing said organic thiosulfate compound by selectively applying on said first metal electrode sufficiently high anodic potential for sufficient time to result in the oxidative self-assembly of said organic monolayers on said first electrode.