LBL assembly method

This chapter describes the non-LBL approaches of tandem assembly and interfacial stabilization for the formation of closed shell structures, with an emphasis on ensembles in which NPs constitute the shell. Tandem assembly is a versatile and environmentally friendly route to the formation of useful NP-shelled capsules. In contrast to sacrificial core templating and LBL assembly methods, tandem assembly has the important differentiating feature that it avoids the incineration or solvent dissolution step to generate the hollow interior of the capsule. Enhancements in optical, mechanical, catalytic, and release properties of such materials hold great promise for their application in photoresponsive delivery systems, catalysis, and encapsulation. Interfacial stabilization routes are found to yield NP-shelled structures in the form of emulsions and foams that have enhanced stability over those from conventional, surfactant-based approaches. Unusual interactions of the NP with fluid interfaces have made possible new structures, such as water-in-air foams, colloidosomes, and anisotropic particles. 

As a powerful methodology to assemble various components into soft supramolecular organizations, the LbL assembly method shows continuous progresses in the fields of drug delivery under the supramolecular concept (Fig. 2.2.5). The LbL method has excellent versatility for the assembly of various kinds of substances [13]. This method covers a wide range of available materials including proteins, nucleic acids, saccharides, virus particles micelles, vesicles, LB films, and other lipid membranes as well as conventional polyelectrolytes, conductive polymers, inorganic nanomaterials, nanocarbons, and dye... 

The layer-by-layer (LBL) assembly method is one technique to combine two electrochromic polymers into a single thin-film composite with fine control over morphology and composition. In the LBL process,... 

The traditional LbL assembly method uses solid substrates to prepare loaded polyelectrolyte microcontainers. In this case the substance encapsulation is a multistage process. It is necessary... 

Another interesting method, first reported by Mamedov " and later refined by others, is the LBL assembly method. This involves building up a layered composite film by alternate dipping of a substrate into dispersions of SWNTs and polyelectrolyte... 

Fig. 5.1 (a) Panoramic, (b) bottom, and (c) magnified cross-sectional SEM images of TNT substrate post-treated by calcination at 450 °C in air for 3 h with corresponding overall cross-sectional view in the inset of (c). Top-view SEM images of (d) Au/TNT, (e) Ag/TNT, and (f) Pt/TNT hybrid nanostructures prepared via LBL assembly method (Reprinted with the permission from Ref. [62]. Copyright 2012, American Chemical Society)... 

As briefly described previously in this chapter, layer-by-layer (LbL) assembly is a versatile method for construction of layered structures from various materials.48,49 Therefore, the LbL technique should be a very useful method for constructing layered mesoscopic structures. The LbL assembly concept was first suggested by Iler,50 but realized and established by Decher and coworkers.51 An outline of this technique is shown in Figure 2.12, where assembly between a cationic polyelectrolyte and anionic... 

The layer-by-layer (LbL) assembly technique based on alternated adsorption of oppositely charged polyelectrolytes, enzymes and nanoparticles is one of simple methods of thin film formation on various surfaces [1,2]. Despite of wide application of this technique, a lack of understanding of some process details still exists. In particular, adsorption kinetics need clarification to optimize the time period and reagent concentration range required for deposition of a saturated layer of adsorbate on various surfaces. 

The buildup of multilayers (HRP/PSS) on (PEI/PSS)2-modified surfaces using the common LbL assembly technique that includes washing and drying the whole film after adsorption of each layer [1-3] was also investigated by the QCM method (Fig. 2). The thickness of the adsorbed film, estimated by means of the Sauerbrey equation in dry state, is 0.77 0.7 nm for one HRP/PSS bilayer. 

Layer-by-layer (LbL) assembly is a unique technique for the fabrication of composite films with precise thickness control at the nanometer scale [111, 112], The method is based on the alternate adsorption of oppositely charged species from their solutions. The attractive feature of this approach is its ability to assemble complex structures from modular components, and integrate them into self-assembling constructions for a wide range of applications. The LbL method has been successfully exploited in the construction of dendrimer biosensors [113,114], The LbL films provide a favorable environment for the intimate contact between the dendrimer and biomolecule (enzymes or proteins), promoting a direct electron transfer between them and the underlying electrodes. 

Screening of interparticle interactions using LbL assembly has also been demonstrated by depositing inert monolayers between each two consecutive metal [11] or magnetic [15] nanoparticle layers. In such methods, only interlayer interactions are screened, so that spatially modulated coupling can be achieved and polarization effects on the reflection coefficient can be obtained. 

In the last decade hollow spheres are extensively studied in the context of application as containers of prolonged action for substances of the different chemical nature dmgs, cosmetics, dye. A number of methods for preparation of microspheres with the sizes ranging from nanometers to micrometers and consisting of various materials are developed. Polyelectrolye capsules have been produced by sequential adsorption of oppositely charged polyelectrolytes, also known as Layer-by-Layer (LbL) assembly onto the surface of colloidal particles followed by core dissolution [1-2]. Most of the capsules applications imply their chemical or physicochemical modification by influence of the ionic strength [3], pH [3], temperature... 

Layer-by-layer (LbL) assembly of proteins or enzymes with polyelectrolytes is a novel general method for protein film fabrication that emerged over the past decade... 

The LbL technique is undoubtedly one of the best methods to incorporate biological components into man-made devices. Therefore, sensor applications must be one of the most promising subjects for LbL assemblies of biomaterials. For example, Leblanc and coworkers used several bilayers of chitosan and poly(thiophene-3-acetic acid) as cushion layers for stable enzyme films [187]. The first five bilayers of the cushion layer allowed for better adsorption of organophosphorus hydrolase than the corresponding adsorption on a quartz slide. The immobilized enzyme becomes more stable and can be used under harsher conditions. The assembled LbL films can be used for spectroscopic detection of paraoxon, an organophosphorus compound. This cushion layer strategy provides a well-defined substrate-independent interface for enzyme immobilization, in which the bioactivity of the enzyme is not compromised. This leads to fast detection of paraoxon and quick recovery times. 

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