Oriented Bacteriorhodopsin/Polycation Multilayers by Electrostatic Layer-by-Layer Assembly

Abstract

The purple membrane (PM) containing bacteriorhodopsin (BR) is a promising biomaterial for many potential optical and optoelectronic device applications. Organized, heterogeneous assemblies using polycationic poly(dimethyldiallylammonium chloride) (PDAC) and PM fragments have been successfully constructed by the spontaneous alternating adsorption of PDAC and PM. The fabrication process of the multilayers was followed by UV−vis absorption spectroscopy and ellipsometry. The results indicate that the deposition process is linear and highly reproducible from layer to layer and that a monomolecular film of PM may be obtained in each PDAC/PM bilayer by controlling the adsorption time. Second harmonic generation measurements from the composite films gave a second-order susceptibility χ(2) of 8.1 × 10-9 esu and confirm that the PM fragments are arrayed with a high degree of orientation and acentric polar order in the films. Atomic force microscopy images provided the surface morphology of sequential layers of PDAC and PM fragments. Relative PDAC/PM bilayer thicknesses of 55 Å were observed, and the homogeneity of the layers was found to improve as the number of layers increased.

Integration of Optical Protein and Quantum Dot Films for Biosensing

“…As shown in Figure 2, AFM images confirm the absorption a single PM monolayer patches which corresponds to the published PM thickness of 5.5nm. Certain sections display membrane overlap with thicknesses around 11nm which has been observed in previous studies [11].…”

“…EXPERIME The bR used in these studies Salinarium strain S9P and prepa standard methods [10] which are de the supplementary section. For the suspended in Milli-Q distilled and d 9.4 to facilitate a strong negative [11]. The QDs used in this study ar capped with thioglycolic acid (TGA negative charge [12].…”

The directed cooperative assembly of proteorhodopsin into 2D and 3D polarized arrays

“…Moreover, instead of 2D reconstitution of proton pumps into bilayers of lipid vesicles with limited and isolated internal volumes, 3D unidirectional assembly offers the sequential addition of proton gradients from individual proteogradient membranes. Because bR in purple membranes is well oriented natively, numerous reports focused on 3D stacking of purple membrane patches using approaches such as electric sedimen-tation (22), Langmuir-Blodgett transfer (23), electric field directed loading (24), sequential deposition with polyelectrolytes (25), etc. Unfortunately, the interdigitation of different patches along the stacking direction and the presence of randomly oriented patches are intrinsic problems.…”

Enzyme-based Electrochemical Biosensors

“…Layer-by-layer selfassembly technique based on electrostatic interaction attracts extensive interest due to its simplicity of the procedure, wide choice of the composition and thickness of the layer on the molecular level . This technique was originally developed by Decher and coworkers (Decher et al, 1992;Lvov et al, 1993) for linear polyelectrolytes and later extended to proteins, enzymes, nanoparticles, and so on (Feldheim et al, 1996;Caruso et al, 1997;He et al, 1998). Using this technique, a glucose biosensor was constructed, in which PMMA dendrimers with modified gold nanoparticles were alternated with poly(vinylsulfonic acid) layers on ITO electrodes (Crespilho et al, 2006).…”