Preparation of Self-Assembled Monolayers

Many techniques are available for the preparation of self-assembled monolayers—detailed discussion of those methods is beyond the scope of this chapter. Finklea has presented a thorough review of the preparation and characterization of self-assembled monlayers [34], Recently Brevnov, Finklea, and Van Ryswyk described a unique method of chemically attaching [4-aminomethylpyridine)Ru(NH3)5] to a previously self-as-sembled mercaptocarboxylic acid monolayer (on gold) [37], and we discuss some results obtained with such systems. Our preparations of systems involving the ferrocene redox moiety [1-3] followed the conventional 

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Ichimura, K., Oh, S.-K., Fujimaki, M., Matsuzawa, Y., and Nakagawa, M. Convenient preparation of self-assembled monolayers derived from calix[4]resorcinarene derivatives exhibiting resistance to desorption. J. Inclusion Phenomena Macrocycl. Cdrem., 35, 173... 

The knowledge about the photocatalytic oxidation of amines is useful also because of the common use of compounds bearing this functionality for the preparation of self assembled monolayers on metal surface. These are subject to degradation that in fact appears to involve a light-induced oxidation of the amino group. This conclusion allows to devise more resistant materials. ... 

The Working Electrode Preparation and Thermal Diffusion Properties 148 Preparation of Self-Assembled Monolayers 150... 

C. Yan, M. Zhamikov, A. Golzhauser, and M. Grunze, Preparation and characterization of self-assembled monolayers on indium tin oxide, Langmuir, 16 6208-6215, 2000. 

Effenberger, F., Gotz, G., Bidlingmaier, B. and Wezstein, M. Photoactivated preparation and patterning of self-assembled monolayers with 1-alkenes and aldehydes on silicon hydride surfaces. Angewandte Chemie-International Edition 37, 2462 (1998). 

In this part we will describe recent achievements in the development of biosensors based on DNA/RNA aptamers. These biosensors are usually prepared by immobilization of aptamer onto a solid support by various methods using chemisorption (aptamer is modified by thiol group) or by avidin-biotin technology (aptamer is modified by biotin) or by covalent attachment of amino group-labeled aptamer to a surface of self-assembly monolayer of 11-mercaptoundecanoic acid (11-MUA). Apart from the method of aptamer immobilization, the biosensors differ in the signal generation. To date, most extensively studied were the biosensors based on optical methods (fluorescence, SPR) and acoustic sensors based mostly on thickness shear mode (TSM) method. However, recently several investigators reported electrochemical sensors based on enzyme-labeled aptamers, electrochemical indicators and impedance spectroscopy methods of detection. 

By their very nature, heterogeneous assemblies are difficult to characterize. Problems include the exact nature of the substrate surface and the structure of the modifying layer. In this chapter, typical examples are given of how surface assemblies can be prepared in a well-defined manner. This discussion includes the descriptions of various substrate treatment methods which lead to clean, reproducible surfaces. Typical methods for the preparation of thin films of self-assembled monolayers and of polymer films are considered. Methods available for the investigation of the three-dimensional structures of polymer films are also discussed. Finally, it will be shown that by a careful control of the synthetic procedures, polymer film structures can be obtained which have a significant amount of order. It will be illustrated that these structural parameters strongly influence the electrochemical and conducting behavior of such interfacial assemblies and that this behavior can be manipulated by control of the measurement conditions. 

Although the above discussion is centered on the synthesis of polymeric osmium and ruthenium complexes, the methods employed are also very successful in the preparation of mononuclear complexes. In this context, the preparation of ruthenium or osmium complexes which are suitable for the formation of self-assembled monolayers (see Section 4.3 above) can be prepared by using the same approach. Starting from the precursor [M(bpy)2Cl2], one chloride atom can be replaced to yield complexes of the type [M(bpy)2Cl L]+, where L is the surface active ligand. In the presence of water, species of the type [M(bpy)2(L)2]2+ are obtained. 

The formation of self-assembled monolayers is a powerful tool for surface modification, and it is useful when we need to control surface hydrophilic-ity or prepare fimctional electrodes, for example. Surface modification with belts composed of monolayers of various hydrophihcities can yield surfaces with hydrophilicity gradients. liquid droplets can move across such surfaces against gravity due to favorable interactions with the monolayer surface (Fig. 4.38). 

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