SAMs crosslinked

Coupling of affinity molecules to surfaces also can be enhanced by the use of discrete PEG linkers. Nishimura et al. (2005) modified an amino surface with a NHS-PEG -maleimide crosslinker to create a hydrophilic self-assembled monolayer (SAM) surface that was thiol reactive for the conjugation of sulfhydryl-modified RNAs. This array then was used to investigate the binding specificity of synthetic kanamycins with selected RNA sequences to prove the specific interaction of ribosomal RNA with this molecule. The PEG linkers on surfaces provide lower nonspecific binding character than alkyl linkers, when preparing SAM surfaces for affinity interactions. 

An alternative to patterning methods that involve chemical reactions such as bond cleavage, crosslinking or oxidation processes, is the use of a binary SAM with one SAM being highly blocking and the other SAM allowing for metal deposition. 

SAMs have been covalently crosslinked by treatment with electron beams, and then removed from the substrates as free-standing films. In an interesting example... 

Figure 28.21 Chemical structures of monomers used for the crosslinking of SAMs by electron beams on gold (52) and silicon nitride (53) and Mo-catalyzed alkyne metathesis or Cu-catalyzed alkyne homo-coupling on silicon oxide- or silicon nitride-coated substrates (54-56).

Figure 2S.23 Scanning electron microscopy images of free-standing nanosheets obtained by etching off a 30nm-thick SiN layer below the crosslinked SAMs of 53 on a prestructured silicon substrate, (a) Arrangement of windows in the silicon wafer after removal of the continuous SiN layer on the opposite...

In this paper we report the application of the pCP technique to a functionalized alkanedisulphide - 11,11 -dithio-bis(succinimidyl-undecanoate) (DSU). We also describe a strategy for rendering etched silicon/gold structures accessible to this reactive crosslinker SAM. We subsequently present the site-specific immobilization of proteins onto such surfaces (Fig. 1) demonstrating the retained functionality of the immobilized protein. The atomic force microscope (AFM) was used to image the immobilized proteins and to determine their amount and spatial distribution on the patterned, template-stripped gold (TSG) surface. 

Figure 1 (A) Schematic section through a chemically microstructured TSG sample after pCP with reactive DSU, formation of a HUT SAM and immobilization of proteins. Primary amines of proteins react with the end groups of the DSU crosslinker (11, ll -dithio-bis(succinimi-dylundecanoate), Fig. 1C bound DSU (thiolate form) with the formation of an amide bond. (B) Schematic section through a microstructured silicon/gold structure after pCP, etching the gold, titanium and silicon, removal of the etch-resistant monolayer, formation of a reactive monolayer and finally reaction with protein.

The free hydroxyl groups exposed on standard AFM tip materials SiOx and sihcon nitride can be directly functionalized using chloro- or ethoxy-substituted alkanesilane chemistry (Fig. 12 left). When proper reaction conditions are used, SAMs can be deposited onto the tip. These procedures are comphcated by crosslinking reactions for the typically used trichloro- or tri-ethoxysilanes, by variations in the number of sUanol groups exposed on the tip surface, and details of the derivatization procedure. 

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