Electrophoretic assembly

R. C. Hayward D. A. Saville I. A. Aksay, Electrophoretic assembly of colloidal crystals with optically tunable micropatterns. Nature 2000, 404, 56-59. 

Different approaches have been used to carry out directed assembly of nanoelements in a desired pattern on a substrate, each approach having different advantages and disadvantages. In electrophoretic assembly, charged nanoelements are driven by an electric field onto a patterned conductor. This method is fast, with assembly typically taking less than a minute however, it is limited to assembly on a conductive substrate [63]. Directed assembly can also be carried out onto a chemically functionalized surface. However, such assembly is a slow process, requiring up to several hours, because it is diffusion limited. Thus, there remains a need for a method of nano element assembly that is both rapid and not reliant on having either a conductive surface or a chemically functionalized surface [64]. 

Phosphate solutions containing fluorides are used for processing steel, zinc and aluminium when assembled together, but chromate solutions are generally preferred when aluminium is treated alone. The increasing use of cathodic electrophoretic painting on steel, however, has led to a reassessment of the basic processes and formulations that might be most effective. 

Morikawa, H., Tsuihiji, N., Mitsui, T., and Kanamura, K. Preparation of membrane electrode assembly for fuel cells by using electrophoretic deposition process. Journal of the Electrochemical Society 2004 151 A1733-A1737. 

Many factors influence the quality of electrophoretic separations, including gel preparation, reagent quality, instrument assembly, electrophoresis conditions, and the nature and quantity of the sample. 

Figure B3.2.2 Electroblotting with a tank transfer unit. The polyacrylamide gel containing the protein(s) to be transferred is placed on the smooth side of the polyethylene sheet (or filter paper sheets) and covered with the PVDF membrane and then a single sheet of filter paper. This stack is sandwiched between two fiber pads and secured in the plastic gel holder cassette. The assembled cassette is then placed in a tank containing transfer buffer. For transfer of negatively charged protein, the membrane is positioned on the anode side of the gel. Charged proteins are transferred electrophoretically from the gel onto the membrane.

The physicochemical characterization of complexes formed between plasmid DNA and products 2 and 3 demonstrates a different behaviour of the new lipid/ DNA complexes, compared to previously described cationic lipids that classically compact DNA and retard DNA in gel electrophoresis. The different nature of the complexes, and especially the unperturbed electrophoretical mobility we have observed, propose them as potential self-assembling systems for gene delivery (Scherman et al., 2001). 

The strong and specific biotin-streptavidin binding was used to assemble biomolecule-functionalized nanoparticles in multilayered structures.67 Application of an electrical field allowed the assembly of multilayer structures by using extremely low concentrations of nanoparticles with minimal nonspecific binding. A microelectrode array was used to facilitate the rapid parallel electrophoretic transport and binding of biotin- and streptavidin-functionalized fluorescent nanoparticles to specific sites. By controlling the current, voltage, and activation time at each nanoparticle adsorption step, the directed assembly of more than 50 layers of nanoparticles was accomplished within an hour. 

Electrophoretic deposition (EPD) is a colloidal process in which the charged colloidal particles are driven by a dc electric field to deposit on a substrate, forming a condensed film. This process is a combination of electrophoresis and deposition (Sarkar and Nicholson 1996). It has a long history and the first application was in 1927 for Th02 and tungsten deposition on a platinum cathode. Recently, photocatalyst semiconductor nanoparticles/microparticles have also been assembled by this... 

The gel and the membrane are then sandwiched between sheets of Whatman 3MM paper and the entire assembly is placed in a Genie Electrophoretic Blotter (IDEA Scientific) according to the manufacturer s instructions. 

Other Useful Applications. It is well known that there are many other important applications of surfactants and organized surfactant assemblies in separation science. Many specific separation processes such as secondary and tertiary oil recovery (500-502), tar sand extraction (503). gas scrubbing and purification (504) and different electrophoretic techniques utilize surface active agents (505). However, space limitations and the existence of several recent review articles preclude further discussion of these applications in this particular overview. 

Figure 15 Schematic of the dual Peltier assembly for rapid thermal cycling followed by electrophoretic analysis on-chip. (Reprinted with permission from Ref. 105.)...

Figure 6-8. Schematic diagram depicting one means of assembling a buffer recycling system for electrophoretic experiments extending over long periods.

Species 21 represents a unique halfway point in oxygenation of Hb in that one of its dimers is fully ligated and the other is fully deoxygenated. The 21 hybrid is formed in vitro by mixing species 01 and 41, as in the example in Fig. 3. One of the two parent Hbs carries an electrophoretic tag to enhance separation based on charge, typically the HbS variant (fS6 Gin— Val). At equilibrinm, the assembly free energy of species 21 is related to the assembly free energies of each parent by... 

Figure 3 Hybridization of deoxy and oxy Hb to form the asymmetrically ligated Hb species 21. (a) Each parent tetramer is in equilibrium with two free dimers. The free dimers may reassemble to the original parent tetramer or may assemble with one another to form the hybrid. The oxy Hb tetramer carries the sickle Hb mutation, on the surface of each p-subunit (yellow), (b) The populations of the three-tetramer species are at equilibrium. Their electrophoretic separation is made possible by their charge difference. If the assembly free energy of the hybrid was the average of that of the two parents, the hybrid population would be 50% of the hybrid mixture, or additive, rather than the 3% observed experimentally.

If plates are difficult to separate cind/or the polymerized gel sticks to plates and tears, siliconize the top plate before assembling the gel mold. Platinum wire electrodes are expensive lnd carbon rods Ccin be substituted. These should be soaked for 10 min in the electrode solutions prior to use, then placed directly on the gel surface and held in position by a glass plate placed on top of them. Samples should be applied at least 1 cm from the anode or cathode rod. Electrophoretic grade acrylamide and iis icrylamide must be used. If poor results are obtained, use a new batch of acrylamide or deionize the stock solution using Amberlite MB-1 resin (BDH). Ampholytes are supplied as 40% (w/v) solutions and they should be used at 1-2% (w/v) final concentration in the gel. Try a 1% concentration first if poor results are obtained, increase the concentration to 2% w/v. 

The assembly of multilayers on SBH particles was observed by measurements of electrophoretic mobility (Fig. 1). Z-potential measurements were taken after each adsorption step. The reversal of charge showed the growth of nanofilms onto surface of SBH microparticles. 

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