Thiol-Modified Surfaces

The present photoelectrochemical deposition/dissolution method is applicable to reversible control of the particle size. A typical application taking advantage of the method is the multicolor photochromism. Additional applications include surface patterning and photoelectrochemical actuator. The patterning is possible by using a thiol-modified silver... 

Kobayashi et al. [91] recently synthesized a phase that is comprised of thiol-modified gold-coated polystyrene particles. An increase in the selectivity of the anthracene-phenanthrene pair was observed on the Cis-Au particle when compared with a traditional monomeric Cis phase with a surface coverage of 3.0 p,mol/m. This isomer pair is not the ideal choice for the determination of shape selectivity however, this synthetic technique should in general lead to dense, ordered phases that are anticipated to yield relatively highly shape-selective chromatographic separations. 

Recent studies have indicated that the base composition of the OND can affect the efficiency of its ability to bind to a surface. This is most probably a consequence of the different affinity that each base shows for any particular surface [21-24], This has been clearly demonstrated in adsorption studies using homo-ONDs (unmodified and thiol modified) onto gold surfaces [23,24]. It was observed that unmodified homo-ONDs adsorb on gold with relative affinities A > C > G > T (Figs. 5 and 6). When performing competitive adsorption experiments with unmodified and thiol modified ONDs,... 

Fig. 6 Average coverage of unmodified hatched bars) and thiol-modified solid bars) homo-OND films after one hour adsorption onto gold surfaces in 1M KH2PO4. The ratio between both bars indicates the ability of nonspecific binding to interfere with specific thiol binding for each sequence, i.e. the relative strength of nonspecific adsorption for each OND [24]...

Therefore, surface modification strategies for the formation of direct silicon-carbon bonds require, first, a special pre-treatment of the silicon surface to prevent oxidation and, second, an activation of the silicon surface for subsequent reaction with organic moieties. This has been achieved by treatment of the silicon surface with hydrofluoric acid to generate a hydrogen-terminated Si(lll) surface, which can further react with unsaturated co-functionahzed alkenes in the presence of UV irradiation or by thermal activation [27,44,45]. Using this method, carboxylic acid modified silicon substrates have been successfully generated and coupled to thiol modified ONDs via a polylysine/sulfosuccinimidyl 4-(M-maleimidomethyl)-cyclohexane-l-carboxylate couphng (Fig. 12). 

SAMs of thiols (and thiol-modified ONDs) can be highly ordered and densely packed, improving the availability of active surface groups (and capture probes) for binding and hybridization. However, dense packing may not always be advantageous in DNA hybrid capture. Steric hindrance effects can occur if the immobilized capture probes are too close together. 

PDMS in its native form does not possess reactive groups that can be used for the covalent attachment of NAs [51]. However, the PDMS surface can be plasma induced oxidized and then fimctionaUzed with organosilanes carrying the desired head group. For example, a PDMS surface has been modified with 3-mercaptotrimethoxysilane to yield a thiol-terminated surface, to which a 5 -acrylamide modified DNA has been covalently attached [52]. See Fig. 13 for a representation of the PDMS surface-modification process. 

The abihty to modify the surface of the CdS nanoparticle within the cavity of the w/o microemulsions has been extended for their immobihzation. CdS nanoparticles (e.g., prepared in AOT/isooctane w/o microemulsions) were immobilized onto thiol-modified aluminosihcate particles [218] and thiol-modified alumina [219] by a simple addition of thiol-modified aluminosih-cates and alumina, respectively, in the micellar solution. The resulting CdS nanoparticles-aluminosihcate composites were used as photocatalysts for H2 generation from 2-propanol aqueous solution. 

Fig. 4.4.7 Models for the surface structures of thiol-modified Agl particles. The shadow represents the inner part of particles. The solid and dashed lines show the surface and adsorbed ions, respectively. Structure A stands for the half-filled model and B for highest coverage model. (From Ref. 10.)...

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