Ultrathin Films of Oriented Bacteriorhodopsin: Nanostructured Films for Investigating the Primary Photoevent in Vision P
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Ultrathin Films of Oriented Bacteriorhodopsin: Nanostructured Films for Investigating the Primary Photoevent in Vision Processes Rigoberto C. Advincula* and Mi-kyoung Park Department of Chemistry, University of Alabama at Birmingham, Birmingham, Al 35294-1240, USA
ABSTRACT In this work, a protocol for investigating Bacteriorhodopsin (BR) biomimetic systems as ultrathin films is presented. BR is one of the most well studied proteins important for investigating the primary photo-event in vision processes. The use of macromolecular assembly approaches for deposition onto solid support substrates, e.g. SiOx, gold- or ITO-coated glass (electrode) provide advantages in that surface sensitive measurements can be used to correlate photocurrent generation, photoelectric response, pH change, chromophore behavior, etc. with protein orientation at interfaces. Membrane and protein morphology were correlated to measurements using surface sensitive techniques, such as atomic force microscopy (AFM), ellipsometry, quartz crystal microbalance (QCM), etc. on solidsubstrate systems. These studies can lead to applications in optobioelectronic devices (biosensors) including patterning in transducer array configurations, where the film structure is important. Hybrid films are possible with supramolecular assembly approaches, e.g. adsorption of membrane with lipidbilayers. We report our initial results on highly ordered and oriented BR protein arrays of controlled thickness, layer order, and orientation. This was done primarily using the alternate polyelectrolyte deposition (APD) or layer-by-layer (LbL) approach to functionalize substrate surfaces.
INTRODUCTION Macromolecular assemblies of functional ultrathin films have growing applications to a number of interfacial science and technological issues.[1] Nanotechnology in bioengineering requires protocols for bringing biosystems and materials into functional units at the nanoscale level. Bacteriorhodopsin (BR) is one of the most well studied proteins important for investigating the primary photo-event in vision processes.[2] Recently, it has also found applications for new types of optobioelectronic devices.[3] BR is a light-sensitive protein in the purple membrane (PM) of Halobacterium salinarium. It has long-term stability against thermal, chemical, and photochemical degradation, together with desirable photoelectric and photochromic properties. As a result, molecularly oriented BR is excellent “natural” materials compared to synthetic chromophores for optobioelectronic thin film devices and applications. For example, a molecular electronic device, which is based on the photoelectric effect in BR, has been designed for motion and direction detection.[4] The photochromic properties of BR on the other hand have been shown to provide the technological basis for recording media for optical and holographic information storage and processing.[5] Thus, it is important to immobilize and process PM fragments onto solid support substrates capable of signal transduction and suitable for device fa
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