Monolayers cross-linked

The cospreading of hexanethiol-capped gold particles with the cross-linking agent 4,4 -thiobisbenzenethiol (TBBT) has been reported as a means of producing cross-linked monolayers of hexanethiol-capped Au nanoparticles [125]. In the presence of TBBT, the... 

Another example of cross-linked monolayers is that of polymerized diacetylenic thiols. Well-packed monolayers of such thiols, HS(CH2)ioC=CC=C(CH2)ioCOOH, can be polymerized in situ by UV irradiation. The polymeric structures obtained are extremely robust and durable compared to similar monomeric layers. They can be repeatedly (more than 30 times) scanned between potentials —0.5 to —1.4 V in 0.5 M KOH without any appreciable signs of desorption. Heating of the films to 200 °C for 1 h showed only ca 15% decrease in the IR intensities of the CH2 peaks, and exposure to 1 M KOH at 100 °C did not affect the integrity of the monolayer306. 

The transfer of alkylsilane monolayers onto mica was explored by Knobler and coworkers [331]. Monolayers of octadecyltrichlorosilane (OTS) were spread at the water-air interface. The trichlorosilane head groups rapidly undergo hydrolysis and cross-linking reactions to produce two-dimensional polysiloxanes on acidic subphases. On less acidic subphases, the polymerization rate is slower and the monolayer can be spread and transferred before the polymerization is significant. The II-A isotherm for OTS spread on... 

This research rests upon oxidative electrochemical polymerization (ECP) of solutions of the functionalized metallotetraphenylporphyrln monomers shown in Fig. 1. These oxidations lead to formation of thin, cross-linked polymeric films of the metallotetraphenylporphyrins on the electrode surface. The films contain from ca. 4 to 500 monolayer-equivalents of porphyrin sites, which are In high concentration (ca. 1M) since the polymer backbone consists solely of the porphyrins themselves as the backbone units. The polymeric films adhere to the electrode and... 

We have observed that such proteins as CaM and bovine serum albumin (BSA) can be developed at the air-water interface to form monolayer protein films. In previous works, the developed BSA monolayer was stabilized by cross-linking with a bifunctional reagent immediately after the preparation of protein monolayer. The BSA thin film thus prepared can be employed as a passive material, e.g., an ultrathin protein film for a matrix of enzyme-linked immunosorvent assays. 

Recently, Genzer and coworkers [85] presented an interesting new approach for the preparation of stable silane-based SAM systems. As a substrate, cross-linked polydimethylsiloxane (PDMS) was oxidized by UV/ozone treatment to yield a thin sihcon dioxide surface. The surface was then treated with fluorinated alkyltrichlo-rosilanes from the gas phase while being mechanically stretched by a certain length Ax. After modification, the elastomer was allowed to relax resulting in a mecdianically assembled monolayer (MAM) at the surface (Fig. 9.8). 

Fig. 9.8 Schematic illustration of the preparation of mechanically assembled monolayers (MAMs). (A) A cross-linked PDMS film is (B) mechanically stretched by Ax (C), oxidized by UV/ozone treatment to yield a thin Si02 sur-...

Flowever, the focus of the major part of the chapters lies on the couphng chemistry used for DNA immobilization. Successful immobihzation techniques for DNA appear to either involve a multi-site attachment of DNA (preferentially by electrochemical and/or physical adsorption) or a single-point attachment of DNA (mainly by surface activation and covalent immobihzation or (strept)avidin-biotin linkage). Immobilization methods described here comprise physical or electrochemical adsorption, cross-linking or entrapment in polymeric films, (strept)avidin-biotin complexation, a surface activation via self-assembled monolayers using thiol linker chemistry or silanization procedures, and finally covalent coupling strategies. 

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