Bilayer electrochemical techniques

Recently, Brzozowska et al. used NR and ex situ electrochemical techniques to characterize an innovative type of monolayer system intended to serve as a support for a bUayer lipid membrane on a gold electrode surface [51]. Zr ions were used to noncovalendy couple a phosphate-terminated self-assembled monolayer (SAM) formed on a gold surface to the carboxylate groups of negatively charged phos-phatidylserrne (PS). This tethered surface was then used for the formation of a PS hpid bilayer structure formed by vesicle fusion and spreading. NR studies revealed the presence of an aqueous environment associated with the tether layer which arises from nonstoichiometric water associated with the zirconium phosphate moieties [52]. 

Murray and his group showed in 198 that bilayer polymeric films and films sandwiched between two electrodes may be used as diodes or triodes via redox conduction that is potential dependent (126,127). Since then, Wrighton s group has carried this concept into the microscopic realm. As discussed above, microelectronic technology was used to prepare arrays of ultramicroelectrodes. These were modified using electrochemical techniques such as electropolymerization or electrodeposition (120,128,129). 

The coupling of biomimetic dynamic interfaces with electrochemical impedance spectroscopy has shown value in the study of ion transport studies across tethered bilayers [56]. Electrochemical impedance spectroscopy may prove valuable used in conjunction with the previously described techniques [57, 58]. Again electrode construction with readily chemically adaptable surface materials such as gold, silver and glass/silica amongst others make this a promising approach for introducing functional interfaces. 

It has been demonstrated recently [4] that BLMs, after suitable modification, can function as electrodes and exhibit nonlinear electronic properties. These and other experimental findings relevant to sensor development and to biomolecular electronic devices will be described in more detail in the present chapter. Also, the potential use of the BLM system together with its modifications in the development of a new class of organic diodes, switches, biosensors, electrochemical photocells, and biofuel cells will be discussed. Additionally, this chapter reports also a novel technique for obtaining BLMs (or lipid bilayers) on solid supports. The presence of a solid support on one side of the BLM greatly... 

As discussed in Sections 2.4 and 2.5.4, the spectral contrast can be increased using MIR-OTEs. This approach has been used, for example, in the ATR studies of adsorption of lipid bilayers to Au [481], p-nitrobenzoic acid on Ag and Au [482] and electrochemical reactions on Au [434], Cu [483], steel [484], Pt [485], and iron [486] electrodes. The ATR technique with a Si MIRE covered by Ag and Au films was applied to the study of thiocyanate adsorption on silver and gold [487]. Enhanced SNR has been reported for the MIR in situ spectra of proteins adsorbed onto a Cu-coated cylindrical internal reflection element [488]. Since the optical path of the beam through a MIR OTE strongly depends on the wavelength, optical schemes with a fixed incident beam are not applicable in this case [362],... 

The technique described above results in bilayers containing trapped solvent which supposedly leads to poor reproducibility in electrochemical measurements. Accordingly, a number of designs have been generated in recent years to produce solvent-free bilayers. However, if measurement trends are all that is required the above will suffice. 

Various planar membrane models have been developed, either for fundamental studies or for translational applications monolayers at the air-water interface, freestanding films in solution, solid supported membranes, and membranes on a porous solid support. Planar biomimetic membranes based on amphiphilic block copolymers are important artificial systems often used to mimic natural membranes. Their advantages, compared to artificial lipid membranes, are their improved stability and the possibility of chemically tailoring their structures. The simplest model of such a planar membrane is a monolayer at the air-water interface, formed when amphiphilic molecules are spread on water. As cell membrane models, it is more common to use free-standing membranes in which both sides of the membrane are accessible to water or buffer, and thus a bilayer is formed. The disadvantage of these two membrane models is the lack of stability, which can be overcome by the development of a solid supported membrane model. Characterization of such planar membranes can be challenging and several techniques, such as AFM, quartz crystal microbalance (QCM), infrared (IR) spectroscopy, confocal laser scan microscopy (CLSM), electrophoretic mobility, surface plasmon resonance (SPR), contact angle, ellipsometry, electrochemical impedance spectroscopy (EIS), patch clamp, or X-ray electron spectroscopy (XPS) have been used to characterize their... 

Bilayer structures have been prepared and investigated with various spectroelectrochemical techniques [307, 486]. In the former report, surface resonance Raman spectroscopy showed typical vibrational features of the involved polymers [PANI and poly(o-phenylenediamine] as already discussed were observed. In the latter investigation, involving PANI/poly(5-chlorine,2-metho3 ani-line), it was concluded that the topmost layer of the polymerized substituted aniline blocks the electrochemical reduction of the inner layer of PANI. This was first deduced from the diminished height of reduction peaks in the CV. Moreover, this was supported by in situ UV-vis spectra that showed typictil bands of oxidized PANI even after formal reduction of the film. 

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