Standard Assembly Procedure

As a standard approach to film preparation, we employ the following steps:

1. Take aqueous solutions of polyion, nanoparticles, or protein at a concentration of 0.1-1 mg/mL and adjust the pH in such a way that the components are oppositely charged.

2. Take a substrate carrying a surface charge (e.g., plates or polymer films covered by a layer of cationic poly(ethylenimine) that may be readily attached to many surfaces).

3. Carry out alternate immersion of the substrate in the component's solutions for 10 min with 1 min intermediate water rinsing. To rinse a sample, use a solution with pH that keeps the polyions ionized.

4. Dry the sample using a stream of nitrogen (Note: drying may hinder the assembly process and it is not necessary for the procedure).

Linear polyions predominately used in the assembly are as follows: polycations—poly(ethylenimine) (PEI), poly(dimethyldiallylammonium chloride) (PDDA), poly(all-ylamine) (PAH), polylysine, chitosan, polyanions—poly(sty-renesulfonate) (PSS), poly(vinylsulfate), poly(acrylic acid), dextran sulfate, sodium alginate, heparin, and DNA. One can grow polymer nanocomposite films by means of the sequential adsorption of different material monolayers that employ hundreds of commercially available polyions. The only requirement is that there be a proper (positive/negative) alternation of the component charges.

Nanoparticle/polyion (or protein) bilayer, D = 5-50 nm

Figure 1. A scheme of the layer-by-layer assembly.

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