Polyelectrolyte PAH

Near-field scanning optical microscopy was applied to study the effect of a 2D array of silver nanoparticles on the spatial distribution and the magnitude of the fluorescence signal enhancement for a monolayer of Rhodamine 6G (Rh6G) and fluorescently labeled polyelectrolyte PAH-F1TC. The results demonstrate inhomogeneous distribution of the fluorescence signal on the surface. 

In this work we employed near-field scanning optical microscopy (NSOM) to study spatially resolved optical properties of a monolayer of silver nanoparticles and their effect on the fluorescence signal of Rh6G dye and fluorescently labeled polyelectrolyte PAH-F1TC. Results of this work indicate that up to 30 times fluorescence enhancement can be achieved in small clusters with average lateral dimension between 100 and 150 nm depending on the excitation wavelength. 

Relatively high dichroic ratio up to 2.3 due to geometry of the molecule (high aspect ratio of Direct Red 80) has been achieved (Advincula et al., 2003). To manufacture these films with PD ADM AC of ca. 100-nm thickness, 100 layers were necessary. Less effective photoorientation of spin-coated and LbL films with other polyelectrolyte (PAH, PEI) was attributed to specific formation of J-aggregates in LbL films. In the LbL films produced from chitosan and Sunset Yellow (dos Santos et al., 2002), spontaneous birefringence of 0.04 for the film of 300-nm thickness was observed however, the value was not affected by the light. This fact underlines the importance of selection of dye and polyelectrolyte. 

Figure 2 Left schematic molecular representation of polyelectrolyte multilayers. Center layer-by-layer electrostatic self-assembly films are alternately dipped in a polycation and a polyanion solution. A rinsing step follows every adsorption step. Right chemical structure of standard polyelectrolytes PAH and PSS.

Serizawa and Akashi [95] analyzed the monolayer adsorption of polystyrene latex particles with cationic polyvinylamine grafted on their surface, while Serizawa et al. [96,97] used commercial anionic latex particles. Both types of particles were adsorbed on polyelectrolyte-coated substrates previously prepared by alternating adsorption of cationic and anionic polyelectrolytes such as polyallylamine hydrochloride (PAH) and polystyrene sulfonate sodium salt (PSS) according to the method described by Decher [164]. Using... 

FIG. 7 Confocal laser scanning microscopy image of a fonr-layer polyelectrolyte/CdTe(S) nanocrystal shell assembled on 1.5-p,m-diameter ME particles. The polyelectrolyte film consists of two bUayers of PAH and PSS. (From Ref. 76.)... 

FIG. 9 Confocal laser scanning micrograph of a hollow polymer capsule. The polymer capsule was obtained from polymer multilayer-templated FDA microcrystals after removal of the colloidal core. The FDA microcrystals were coated with SDS and 11 polyelectrolyte layers [(PAH/PSS)3/PAH/ (PSS/PAH-FITC)2]. (PAH-FITC = PAH labeled with fluorescein isothiocyanate.) The microcrystal core was removed by exposure of the coated microcrystals to ethanol, causing solubilization of FDA. 

The inner structure of polyelectrolyte multilayer films has been studied by neutron and X-ray reflectivity experiments by intercalating deuterated PSS into a nondeut-erated PSS/PAH assembly [94, 99]. An important lesson from these experiments is that polyelectrolytes in PEMs do not present well-defined layers but are rather interpenetrated or fussy systems. As a consequence, polyelectrolyte chains deposited in an adsorption step are intertwined with those deposited in the three or four previous adsorption cycles. When polyelectrolyte mobility is increased by immersion in NaCl 0.8 M, the interpenetration increases with time as the system evolves towards a fully mixed state in order to maximize its entropy ]100]. From the point of view of redox PEMs, polyelectrolyte interpenetration is advantageous in the sense that two layers of a redox polyelectrolyte can be in electrochemical contact even if they are separated by one or more layers of an electroinactive poly ion. For example, electrical connectivity between a layer of a redox polymer and the electrode is maintained even when separated by up to 2.5 insulating bUayers [67, 101-103]. 

While the structure of nonredox polymer and polyelectrolytes thin layers has received much attention in the past [116, 117], only recently has a molecular theory able to treat, from a molecular point of view, redox polyelectrolytes adsorbed on electrodes, been presented [118-120]. The formulation of the theory, its scope, advantages and limitations will be discussed in detail in Section 2.5.2, and therefore we will limit ourselves to show here some predictions that are relevant for the understanding of the structure of polyelectrolyte-modified electrodes. The theory was applied to study the particular system depicted in Figure 2.5, which consists of a single layer of PAH-Os adsorbed on a gold surface thiolated with negatively charged mercapto... 

Figure 2.5 Schematic representation of the Au/MPS/PAH-Os/solution interface modeled in Refs. [118-120] using the molecular theory for modified polyelectrolyte electrodes described in Section 2.5. The red arrows indicate the chemical equilibria considered by the theory. The redox polymer, PAH-Os (see Figure 2.4), is divided into the poly(allyl-amine) backbone (depicted as blue and light blue solid lines) and the pyridine-bipyridine osmium complexes. Each osmium complex is in redox equilibrium with the gold substrate and, dependingon its potential, can be in an oxidized Os(lll) (red spheres) or in a reduced Os(ll) (blue sphere) state. The allyl-amine units can be in a positively charged protonated state (plus signs on the polymer...

As was mentioned before, charge compensation during oxidation in redox polyelectrolyte systems can be achieved by anion uptake or cation release. For example, for a PAH-Os/PVS-modified eledrode, we can write ... 

Figure 2.25 Dependence of the catalytic current for the oxidation of p-D-glucose mediated by the redox polyelectrolyte film for different number of COx layers self-assembled with (PAH-Os) (COx) (n=m = 2, 4, 6). Taken from [182].

For the modification of the gold surface different chemical and biological substances (dodecanethiol, lectins, dextran sulfate DS, with the mass of 5 kDa and polyelectrolytes) were used. The mercaptane layer was formed in ethanol atlO" M concentration of thiol. Polyaniline hydrochloride (PAH), Aldrich , USA, was used to cover the transducer surface by a water insoluble polymer. Lectins from Phaseolus vulgaris (PLA), Solanum tuberosum (STA), Helix pomatia (HPA) and Tuberosum vulgaris (WGA) were immobilized on the surface pre-treated with dodecanethiol or PAH. These lectins were used for the immobilization of glycoproteins. Blocking of the free binding sites was carried out with 1% bovine serum albumin (BSA). 

Figure 12.5 (a) Layer-by-layer deposition of glucose oxidase and the polyallylamine Os3 +n + -polypyridine polyelectrolyte on the electrode, (b) Typical catalytic current responses for different glucose concentrations obtained by self-assembled nanostructured thin films based on different architectures (i) PAH/Os/GOx, (ii) cysteamine/GOx/PAH-Os, (iii) PAH/GOx/ -Os, and (iv) (PAH-Os)2/(GOx)i. All measurements were performed in 0.1 M tris buffer at pH 7.5. Part (b) Reproduced with permission from Ref. 34a. Copyright Wiley-VCH Verlag GmbH Co. KGaA. 

We used polyelectrolyte multilayer formed from polyallylamine hydrochloride (PAH) and PSS successfully for templating deposition of colloidal particles, as displayed in Fig. 12. The wavelength of the wrinkles was adjusted by the number of polyelectrolyte deposition cycles and, accordingly, single lines of particles or double lines, as well as other geometries, could be achieved [70],... 

Protein aggregates [107, 109, 121] or dye crystals [122-126] can serve as templates for LbL polyelectrolyte adsorption. Chymotrypsin aggregates encapsulated by PSS and PAH deposition contain a high protein amount and the enzyme keeps its bioactivity [107], The aggregates prepared in this manner have high incorporation efficiency and a protein content of 50-70% [109]. An encapsulated catalase has been shown to be stable against protease degradation [121],... 

Fig. 11 (a) Optical microscopy images of the release from ibuprofen crystals covered with a (CHI/dextran sulfate)is shell 1 before dissolution 2 during dissolution and 3 after removal of the crystal cores. The mean size of the encapsulated ibuprofen microcrystals is 15.3 am. Reproduced from [112]. (b) Fluorescence increases with time, obtained by dissolving fluorescein crystals covered with shells of different thicknesses (9, 13, 15, and 18 polyelectrolyte-deposited PSS/PAH layers). The release from the native (uncovered) fluorescein crystals is shown as 0. Reproduced from [122]... 

Fig. 10 Example of a contact-killing and microbe-releasing surface. The scheme shows the design of a two-level dual-functional antibacterial coating containing both quarternary ammonium salts and silver. The coating process begins with LbL deposition of a reservoir made of bilayers of PAH and PAA. (A) Cap region made of bilayers of PAH and SiC>2 nanoparticles (NP) is added to the top. (B) The SiC>2 nanoparticle cap is modified with a quarternary ammonium silane (QAS) PEM polyelectrolyte multilayer. (C) Ag+ is loaded into the coating using the available unreacted carboxylic acid groups in the LbL multilayers. Scheme was reproduced from [138]...

Figure 4.32 Structure of the stratified film of the polymer as obtained from neutron reflectivity experiments shown in terms of volume fractions distances are normal to the substrate surface [(PSS-h7-PAH)3-PSS-d7-PAH]. Above 900 A, the distribution of water associated with the different polyelectrolytes is indicated. Reprinted with permission from M. Losche, J. Smitt, G. Decher, W.G. Bouwman and K. Kjaer, Macromolecules, 31, 8893 (1998). Copyright (1998) American Chemical Society...

Fig. 27 Schematic illustration of the LbL self-assembly of a charged poly(phenylacetylene) with induced macromolecular helicity. a An excess of the one-handed helical sense is induced in 30 upon complexation with the optically active (S)-75 in water, b An induced helical 30 can be LbL assembled with an achiral polyelectrolyte having opposite charges (PAH), resulting in multilayer thin films with an induced macromolecular helicity on a substrate...

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