Deposition Langmuir-Blodgett technique

Rees and co-workers23 first studied the effect of the deposition of thin HRI overlays onto LPGs by analyzing the wavelength shift of the attenuation bands. The Langmuir-Blodgett deposition technique was exploited to deposit an incrementally thicker overlay (up to few hundreds of nanometers) of an organic material whose refractive index was 1.58. 

In the case of adsorption from solution, the surfactant layers are in equilibrium with the solution and will de-sorb on dilution. However, it would be very useful to produce adsorbed layers in both air and water, which will remain adsorbed. This can be achieved using the Langmuir-Blodgett deposition technique. The technique is based on the observation that if a surfactant, which is insoluble in water, is dissolved in a volatile, non-aqueous solvent and then spread on water, an insoluble monolayer of orientated surfactant molecules will remain at the air/solution interface. The effect of the spreading surfactant and its surface film pressure can be dramatically demonstrated by spreading hydrophobic talc powder on a clean water surface and then placing a... 

Detailed information about the components of the second-order susceptibility y2)(-2w to, w) can be obtained from second harmonic measurements on well-defined samples such as single crystals or oriented thin films, the latter obtained by procedures such as the asymmetric Langmuir-Blodgett deposition technique or electric-field poling of NLO chromophore-doped polymers.31 In the case of single-crystal samples, the second harmonic is... 

The Langmuir-Blodgett deposition technique shows excellent promise for the assembly of films with noncentrosymmetric ordering and Coo symmetry. A system that was reported recently (3i) is shown in Figure 6.11. In this system, monolayers of the hemicyanine dye and the nitrostilbene... 

Development of a sensor for neurological ly active compounds using the vesicle system characterized here necessitates stabi i Ization of a functional receptor system onto a sol id substrate. Possible methods for this stabi I Ization are direct covalent attachment via the protein or the Iipid componentSt fusion of vesicular structures with the substrate(26), or incorporation of the protein Into a monolayer at an alr/water interface and transfer of the monolayer onto the substrate by Langmuir-Blodgett deposition techniques(27). 

The Langmuir-Blodgett (LB) technique was successfully applied for the deposition of thin protein layers (Langmuir and Schaefer 1938, Tiede 1985, Lvov et al. 1991). LB organization of protein molecules in film not only preserved the structure and functionality of the molecules, but also resulted in the appearance of new, useful properties, such as enhanced thermal stability (Nicolini et al. 1993 Erokhin et al. 1995). 

It was indeed shown recently that it is possible to deposit DNA-aliphatic amine complexes onto solid substrate via the Langmuir-Blodgett (LB) technique (Erokhin et al. 

Figure 11.5. Langmuir-Blodgett (LB) technique-assisted NW assembly (a) Schematic of LB-guided assembly. NWs are floated on a water surface and compressed through computer guided pressure, (b) SEM image of silver NWs deposited on Si wafer. Reprinted with permission from Ref. 54. Copyright 2003 American Chemical Society.

Immobilization of DNA on silver surfaces of TSM through modification was reported by Yao and co-workers with thioglycollic acid [55] and didodecyl ditiono-oxamide and bovine serum albumin [56]. The Langmuir-Blodgett (LB) technique was used to deposit ssDNA-containing films on QCM crystals by Nicolini et al. [57] and the nanogravimetric hybridization assay was confirmed by fluorescent measurements. 

In Langmuir-Blodgett deposition (Fig. 10.24e), a film of molecules (with amphiphilic properties) is forced in a densely packed layer at a liquid-air interface or at a liquid-liquid (lipophilic/hydrophilic) interface. The substrate (submerged into the liquid beforehand) is pulled from the liquid to air to adsorb a monolayer. With this technique, the monolayer is forced into an organization by narrowing the organization area with movable sidewalls. The technique has been particular successful on molecules with liquid crystal properties [133, 87],... 

Alegria and Dutton used the Langmuir-Blodgett (LB) technique to deposit multiple (mono) layers of either the Rp. viridis reaction-center complex or of the corresponding chromatophores, in either case dispersed in a phospholipid matrix. The absorption spectmm of the LB-film was almost identical to that of the reaction center complex in solution, as shown in Fig. 10 (A), indicating that the in vitro properties of the photosynthetic apparatus are stable and essentially retained in the LB-films. The authors used a combination of redox potentiometry and absorption spectroscopy to identify the four Rp. viridis hemes and their redox potentials, and also determined their orientations by linear-dichroism measurements. 

High-resolution circuitry and active devices employing Langmuir-Blodgett film techniques or polymer-based transistors are being considered for the sophisticated electronics required in future vehicles. Temperature or energy balance in the vehicle could be controlled through conductive polymers or semiconductor deposits on electrochromic windows. Electroluminescent liquid crystals and fluorescent and electrochromic materials used for visual displays show promise for future development. 

An extension of artificial membranes for ion selective electrochemical work was the construction of biomimetic ion channel sensors [65]. These devices were based on Langmuir-Blodgett deposition of charged lipid membranes onto a glassy carbon electrode. This work indicated that a conductive zone can be opened reversibly by a stimulant-membrane interaction by surface charge alterations. This work has demonstrated how the concept of the conductivity measurement could be extended to the more common and useful technique of cyclic voltammetry. 

Most devices based on Pc are fabricated by vacuum deposition, i.e. thermal evaporation. However, recent solution-based Langmuir-Blodgett (LB) techniques have also been used. LB-films of 25h-251 gave poor (10 cm V s for 25j) to moderate (1.7 x 10 cm V s for 251) mobilities (Figure 3.1.9).[162-164] More recently, high mobilities of 0.24-0.60 cm V s have been observed for LB films of amphiphilic tris(phthalocyaninato) rare earth triple-decker complexes, 25m-25o.[165] OFET characteristics have also been reported for porphyrin derivatives, 25p-q with mobilities of 2.2 x 10 cm V s and 0.012 cm V s, respec-tively.[166-168] LB-prepared thin films of Cyclo[8]pyrrole (25r), an extended porphyrin-like molecule, also exhibited a high mobility of 0.68 cm V s, but with a low on/off ratio.[169]... 

The Langmuir-Blodgett (LB) technique has been employed to prepare membranes with well-defined molecular packing. Octadecylamine was selected as an amphiphile which forms chaiged mono-layers on the water surface and has good insulating properties when deposited onto electrically conductive substrates, indium-tin oxide (ITO) layer. 

It has been observed that the surface of the conducting polymer plays an important role in the effective immobilisation of the desired enzyme. The Langmuir-Blodgett (LB) technique can be successfully applied to deposit a desired monolayer with the desired orientation of the biomolecules/enzymes [142-145]. Ramanathan and co-workers [146] have utilised the polyemeraldine base LB films for the immobilisation of GOD. These films have been shown to function as amperometric glucose biosensors and have a linear range from 5 to 50 mM. LB films of PT immobilised with GOD and urease have also been prepared for application to respective biosensors [147, 148]. 

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