Self-assembled monolayer technique

The strong interaction with the solid surface sometimes compensates for a lack of self-assembling ability for some components (Fig. 4.36). Molecules whose structures are much different to those of typical amphiphiles can be used in this method. In addition, immobilizations of dyes, proteins and nucleic acid are possible using this self-assembled monolayer technique. These self-assembled monolayers have great potential for a wide range of applications. 

In 1995, Natan et al. reported that Au and Ag nanoparticles adsorbed onto an organosilane-polymer-modified Si substrate could be used as a SERS-active substrate [97]. Subsequently, in 2001 the same authors [98] proposed a novel approach based on the self-assembled monolayer technique which allows the preparation of regularly arranged monodispersed colloidal Au and Ag nanoparticles on functionalized metal or glass substrates. It is now possible to synthesize or fabricate metal nanostructures of various shapes and sizes with a narrow size distribution. Nanoparticles assembled on an electrically conductive substrate can significantly improve the surface uniformity of the EC-SERS substrate. Therefore, use of nanoparticle sols or assembled nanoparticles as SERS substrates has expanded very rapidly during recent years [92]. 

Johnson and coworkers [6], in their original paper on the JKR theory, reported the measurements of surface energies and interfacial adhesion of soft elastomeric materials. Israelachvili and coworkers [68,69], and Tirrell and coworkers [62, 63,70,88-90] used the SFA to measure the surface energies of self-assembled monolayers and polymer films, respectively. Chaudhury and coworkers [47-50] adapted the JKR technique to measure the surface energies and interfacial adhesion between self-assembled monolayers. More recently, Mangipudi and coworkers [55] modified the JKR technique to measure the surface energies of glassy polymers. All these measurements are reviewed in this section. 

As reviewed so far, the contact-mechanics-based techniques (JKR and SFA methods) have been effective in the understanding molecular level mechanisms related to the adhesion of elastomers and in measuring the surface and interfacial energies of polymers and self-assembled monolayers. The current work in this area is aimed at understanding contact induced interfacial rearrangements and the role of specific interactions. The recent progress of these studies is discussed in this section. 

The AFM tip plays also the dominant role in another technique where CH3 end groups of a self-assembled monolayer of alkyl chains are oxidized by a conductive tip... 

For transition and precious metals, thiols have been successfully employed as the stabilizing reagent (capping reagent) of metal nanoparticles [6]. In such cases, various functionalities can be added to the particles and the obtained nanoparticles may be very unique. It is well known that thiols provide good self-assembled monolayers (SAM) on various metal surfaces. When this SAM technique is applied to the nanoparticle preparation, nanoparticles can be covered constantly by functionalized moieties, which are connected to the terminal of thiol compounds. 

As the analytical, synthetic, and physical characterization techniques of the chemical sciences have advanced, the scale of material control moves to smaller sizes. Nanoscience is the examination of objects—particles, liquid droplets, crystals, fibers—with sizes that are larger than molecules but smaller than structures commonly prepared by photolithographic microfabrication. The definition of nanomaterials is neither sharp nor easy, nor need it be. Single molecules can be considered components of nanosystems (and are considered as such in fields such as molecular electronics and molecular motors). So can objects that have dimensions of >100 nm, even though such objects can be fabricated—albeit with substantial technical difficulty—by photolithography. We will define (somewhat arbitrarily) nanoscience as the study of the preparation, characterization, and use of substances having dimensions in the range of 1 to 100 nm. Many types of chemical systems, such as self-assembled monolayers (with only one dimension small) or carbon nanotubes (buckytubes) (with two dimensions small), are considered nanosystems. 

Polyamidoamine (PAMAM) dendrimers (G3.5-G10) were used by Tsukruk et al. [25,26] to fabricate self-assembled monolayers by an electrostatic deposition techniques [27],... 

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. 

Using this deposition technique, TiOi was deposited onto patterned self-assembled monolayers [49]. Thioacetate-terminated trichlorosilane monolayers... 

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