Thiol-modified supports

Radical addition of thiol or thiol-modified support to the vinyl group gives the respective thioether linkage 34 and represents one of the most convenient ways to immobilize Cinchona alkaloids [163, 172]. There are also few examples of platinum-catalyzed hydrosilylation of Cinchona alkaloids toward 11-silyl-substituted derivatives 35 with the use of monomeric silanes or polysiloxane polymers [173-175]. De Vries reported rhodium-catalyzed hydroformylation of the four main members of Cinchona alkaloids carried out on a hundred gram scale. Under optimized condition, linear aldehydes 36 were selectively obtained with the yield over 80% [176]. 

Fig. 9 Covalent attachment of thiol-modified DNA oligomers to amino-silane derivatized supports...

As a class, the cross-linkers used to attach thiol-modified oligonucleotides to solid supports are hetero-bifunctional, meaning that they possess functional groups capable of reaction with two chemically distinct functional groups, e.g., amines and thiols. Hetero-bifunctional cross-linkers can covalently bind two distinct chemical entities that would otherwise remain unre-active towards each other [8]. 

A similar approach was used to prepare a thiol-modified HA (3,3 -dithiobis-propanoic dihydrazide) (HA-DTPH) that was subsequently reacted with an Arg-Gly-Asp (RGD) sequence and then cross-linked with PEGDA to create a biomaterial that supported cell attachment, spreading, and proliferation (73). 

On the basis of the previous DNA assay, the Mirkin group has developed a silver staining method to enhance the sensitivity. In the sandwich-type format, thiol-modified oligonucleotides were attached to the soUd support These oligonucleotides and the DNA targets hybridized with the DNA functionalized AuNPs. The reduction of the added silver ions was catalyzed by the AuNPs. The concentration of the DNA target was proportional to that of silver, which was visualized with a flatbed scanner. This method was... 

Type IV materials exhibit unique ion-exchange properties supplemented by RP characteristics, so that they may be considered as RP-modified ion-exchange materials. Lammerhofer et al. [59] have developed a number of RP/weak anion exchanger (WAX) materials consisting of a selector immobilized onto thiol-modified silica. In these phases, the WAX site is located at the top of the lipophilic layer and is linked to the silica support via a lipophihe spacer with polar-embedded amide or sulfide groups. These columns, however, are not commercially available. 

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. 

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