Gold-thiol monolayers applications

It will be going beyond the scope of the present review to give a detailed description of the techniques available, or to provide a comprehensive list of all methods used in surface analysis. Such information could be found in a number of monographs and review papers414,15. Analytical Chemistry publishes reviews every two years on the latest developments in surface characterization methods16. We will attempt to discuss briefly the most powerful and most readily available methods applicable to routine gold-thiol monolayer analysis with particular emphasis on the kind of information which can be obtained from these systems. 

Another important area where gold-thiol monolayers might find promising applications is gas- and biosensing. Simple sensors sensitive to certain types of compounds, based on such detection methods as surface plasmon resonance or surface acoustic wave, have been described454,455,531-533. This type of device is usually made of a gold plate coated with a functionalized monolayer. The terminal functional group of such a monolayer is responsible for selective interactions with the analyte, and adsorption of the latter is then detected by the appropriate method. 

Gold-thiol monolayers And a very broad range of applications in various fields of research deahng with interfacial phenomena. The potential outlook in some areas has been reviewed, and the references are given in the next sentence. Appheations include microelectronics , sensor devices , biochemical research , various uses of patterned films , adhesion and friction-related problems , anchoring of hq-uid crystals, corrosion inhibition and electrochemistry. General discussion of potential applications can be found in other references . Electrochemical appheations are discussed in Section Vll.C. In this section we briefly describe some of the most conunon areas of appheations. 

Oxidation of monolayers is greatly increased under UV irradiation. Irradiation of alka-nethiol monolayers with a mercury lamp at ca 0.16 W cm for 25 min results in 60% oxidation of the thiolate group to the sulphonate. Irradiation at 3 W cm for 1 h leads to the complete oxidation of the monolayers . The sulphonate monolayer obtained can be removed by rinsing with neat solvent or by exchange with solution of another thiol. This method, along with electrochemical desorption (vide infra), is conveniently used to remove thiolate monolayers from the gold surface . The application of these techniques to generate patterned monolayers is discussed in Section X. 

M. Buck reviews in great depth the literature on self-assembled monolayers (SAMs) of thiols on gold, a classic means of surface modification. The wide variety of functional groups that is provided by synthetic chemists makes thiol-SAMs an exciting playground for applications where the gap between two worlds, the inorganic and the organic, needs to be closed. Examples are molecular electronics and biochemistry. 

Patterns of ordered molecular islands surrounded by disordered molecules are common in Langmuir layers, where even in zero surface pressure molecules self-organize at the air—water interface. The difference between the two systems is that in SAMs of trichlorosilanes the island is comprised of polymerized surfactants, and therefore the mobility of individual molecules is restricted. This lack of mobility is probably the principal reason why SAMs of alkyltrichlorosilanes are less ordered than, for example, fatty acids on AgO, or thiols on gold. The coupling of polymerization and surface anchoring is a primary source of the reproducibility problems. Small differences in water content and in surface Si—OH group concentration may result in a significant difference in monolayer quality. Alkyl silanes remain, however, ideal materials for surface modification and functionalization applications, eg, as adhesion promoters (166—168) and boundary lubricants (169—171). 

Self-assembled monolayers (SAMs) on gold and other metal surfaces have been extensively studied in biosensors applications.28-30 The thiol-gold chemistry is well known and is much easier controlled than organosilane chemistry (Fig. 14.4).31 34 The... 

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