SAM Preparation

Gold substrates were dipped in a solution of 8.4 mmol/L hexadecanethiol in ethanol for 1 min, rinsed with ethanol, and cleaned by a hydrogen plasma. A 1 mM solution of each of 1-11 in absolute THF as well as absolute ethanol, was prepared under a stream of nitrogen. Substrates were stored in these solutions for 24 h in the absence of light, rinsed with ethanol, blown dry under a stream of nitrogen and stored in the dark until further use. 

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Figure 16.2 Three different approaches used by Crooks et at. to immobilize PAMAM dendrimers on Au surfaces (A) Direct attachment, using amine-Au interactions [39-41 ] (B) covalent attachment on a SAM prepared from alkylthiols using multiple interactions [42] (C) covalent attachment on a SAM prepared from alkylthiols using only one or a few connections [43]...

Wasserman [186] has described the use of both low-angle X-ray reflectivity and ellipsometry for the determination of thickness of Cio-Cig SAMs prepared on surface silanol groups of silicon plates. Ellipsometry is based on the reflection of polarized light from a sample and depends on the sample s thickness and refractive index. X-ray reflectivity measures the intensity of X-rays reflected from a surface (or interference pattern) that is characteristic of the distance between interfaces. The thickness of the SAMs was consistent with fully extended alkyl chains with all-trans conformations and excellent agreement was observed between the two methods. 

We denote the SAMs prepared from these compounds as ODS-, FAS3-, FAS 17- and AHAPS-SAMs hereafter. 

Self-assembly of one- or two-component alkylthiol SAMs provides a convenient tool for tailoring, at a molecular level, the chemical reactivity of a gold surface by choosing and modulating the nature and amount of surface-bound chemically reactive groups (e.g., -OH, -COOH, or -NH2) in the monolayer. Particularly, mixed alkylthiol SAMs prepared by coadsorption of alkylthiols... 

Scheme 11. Idealized sketch showing the electroen matic oxidation of L-lactate at gold modified electrode surfaces, (a) Lactate dehydrogenase bound to CB-terminated alkylthiol SAMs prepared by covalent attachment of CB to 3-mercaptopropionic acid SAM derivatized with 1,4-diaminobutane. The electroenzymatic oxidation of lactate is observed only in the presence of soluble coenzyme (NAD" ") and a redox mediator (phenazine methosulfate) [215]. (b) Lactate deh3tdrogenase bound to NAD-terminated alkylthiol SAMs prepared by covalent attachment of Af -(2-aminoethyl)-NAD to a cystamine SAM derivatized with pjrrroloquinoline quinone. The reconstituted enzyme is electrically wired to the electrode surface via two NAD" -binding pockets involved in the affinity-binding surface reaction [242].

On the basis of the SEIRAS experiments, the difference in the promotion activities of the SAMs prepared under different conditions was explained as follows the sulfide is strongly adsorbed on Au and prevents the adsorption of 4-PySH. However, since the sulfide concentration is very low, it takes some period of time for its adsorption. Accordingly, by employing the conditions under which 4-PySH can be adsorbed quickly, the electrode surface can be covered with 4-PySH with less interference from sulfide. 

A convenient strategy combines the use of prepatterned SAMs prepared by iCP and bilayer formation by vesicle fusion (Sect. 2.3.1) [164]. As shown schematically in Fig. 19, this approach comprises, in a first step, the patterning of a SAM (a cholesterol-terminated thiol is transferred to the gold substrate, the remaining areas are back-filled with the hydrophilic hydroxy-... 

Fig. 19 Schematic drawing of bilayer deposition by vesicle fusion on patterned SAMs prepared by microcontact printing. (Reprinted with permission from [164], copyright (1999), American Chemical Society)...

For achieving chemical selectivity, tiie cantilevers are modified with appropriate chemically selective coatings. The appropriate self-assembled monolayers were immobilized on tiie gold side of the cantilever as discussed below. In all applications, tire Si cantilevers (with Au on one side) were cleaned in piranha solution (7 3 H2SO4 (96%) H202 (30%)) for 1 min and rinsed with H2O (3 times) and EtOH (2 times) before measurement or SAM preparation. 

Monolayers as modifiers on electrode surfaces are prepared by sorption techniques. Self-assembled monolayer s (SAMs) form by spontaneous adsorption of precursors on the electrode substrate with an ordered orientation by interaction of certain molecule areas protruding from the sorption plane [109—112] most popular are SAMs prepared by thiol compounds on gold surfaces, but also SAM formation on CPEs is possible. Langmuir-Blodgett layers (LBLs) are monolayers made by surfactants by adsorption from the surface of a solution [113]. Highly ordered multistacked structures from polyelectrolytes can be obtained by layer-by-layer deposition, where the ensuing plane of the stack can be immobilized by sorption of a countercharged polyelectrolyte [114-116]. 

Fig. J (a) Agold (111) surface deposited on mica at 300 °C (mean roughness, 32.5 A), (b) A TSG surface (mean roughness, 2.6 k). (c) N-palmitoylcysteamine SAM prepared from disulfide...

Preparation from Liquid and Supercritical Carbon Dioxide A novel type of SAM preparation technique with liquid and supercritical carbon dioxide has been developed very recently by Weinstein et al. [225, 226). They have demonstrated that environment-friendly mixed solvents such as supercritical carbon dioxide-ethanol can be used to control the properties of SAMs, such as the defect density by simply altering the composition of the mixed solvents [226]. 

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