Bacteriorhodopsin Films Research Articles

Protein-based integrated optical switching and modulation

The static and dynamic response of optical waveguides coated with a thin protein film of bacteriorhodopsin was investigated. The size and kinetics of the light-induced refractive index changes of the adlayer were determined under different conditions of illumination. The results demonstrate the applicability of this protein as an active, programmable nonlinear optical material in all-optical integrated circuits.

The intensity dependent refractive index change of bacteriorhodopsin measured by the Z-scan and phase-modulated beams techniques

Abstract A comparative analysis of intensity dependent refractive index change of a thin polymer bacteriorhodopsin (bR) film by the Z -scan and phase-modulated beams techniques is given. The analysis is conducted at two excitation wavelengths, λ =543 and 633 nm, corresponding to the opposite slopes of the bR ground-state absorption band resulting in opposite signs of the refractive index change. A three-level model of the bR photo-cycle is proposed to describe the experimental data.

Orientationally Enhanced Photocurrent and Electrooptic Modulation Effects in Bacteriorhodopsin/Polyvinyl Alcohol Thin Films

Polymeric films of bacteriorhodopsin, formed by embedding purple membrane fragments into a poly(vinyl alcohol) matrix without field poling, exhibit modulated photocurrent and electrooptic effects when an AC modulating rectangular voltage or a sinusoidal voltage is applied across the films. When the modulating frequencies are lower than 100 Hz, both effects are enhanced by the orientation of the purple membrane fragments and exhibit two different orientational time constants. The orientational enhancement at low frequencies (∼7.1 Hz) arises from the permanent dipole moments of membranes, and the enhancement at higher frequencies (∼74.8 Hz) is attributed to the induced dipole moments of the purple membrane molecules. For quantitative analyses of these processes, a theoretical model is proposed. From the combination of model calculations and fitted experimental results, we determine that the permanent dipole moment of the membrane material is ∼33 kD and the induced dipole moment is ∼10-13 cm3. We also demonstrate that when a poling field is applied across the films, the electrooptic coefficients are increased linearly with increasing field strength.

Mechanisms of pulse response and differential response of bacteriorhodopsin and their relations.

Bacteriorhodopsin (BR) films are oriented and deposited on indium tin oxide conductive glass by using electrophoretic sedimentation and Langmuir-Blodgett methods to construct sandwich-type photocells, respectively. The pulse response photoelectric signal of the BR photocell under pulsed laser and the differential response photoelectric signal under irradiation of interval light are measured. The origins of these two types of photoelectric responses and their correlations are analyzed. The pulse response signal initiates from the ultrafast charge separation of the retinal and the proton translocation followed by the deprotonation and reprotonation of the Schiff base and its surrounding amino acids. This is a quick response and is the preceding reaction of the differential response. The differential response signal is caused by the charging and discharging of the continuous proton current of the BR light-driven proton pump at light-on and light-off, which is a slow process. The differential response is related to not only the construction of the BR photocell but also the coupling mode of measurement. To observe the differential response signal, the BR photocell must have large enough B3 and B3' components in its pulse response as well as an alternative coupling mode to measure it.

Reflection-type polarization holograms in bacteriorhodopsin films for low-light recording

Reflection-type polarization holograms with phase-conjugated readout are very useful for low-light recording with bacteriorhodopsin (BR) films. The dependence of reflection-type holograms with parallel and orthogonal recording beams on their intensity ratio (1:1-1:20) was investigated. It was found that for orthogonally polarized beams the phase-conjugated signal depends significantly less on the beam intensity ratio than predicted by coupled-wave theory. This finding is of particular relevance for recording of very low object-beam intensities with BR films, e.g., in interferometry, where signals with a high signal-to-noise ratio, owing to the different polarizations of the scattered light and the signal, and with low dependence of the diffraction efficiency on the ratio between the reference and object-beam intensities are obtained. With this asymmetric recording process, holograms were recorded successfully in BR films with a good signal-to-noise ratio at exposures (from the object side) as low as 50muJ/cm(2) . These exposures are in the range of those typically used for silver halide films.

Real-time self-induced nonlinear optical Zernike- type filter in a bacteriorhodopsin film

We propose the use of a nonlinear bacterior- hodopsin film to self-induce a Zernike-type filter in robust optical phase-contrast systems. The device requires rela- tively low light intensity levels (as low as 200 nW/cm 2 )a t wavelengths around 633 nm and can contrast dynamical phase distributions. © 2001 Society of Photo-Optical Instrumentation

Grating Formation in 13-demethyl Bacteriorhodopsin Film

Holographic properties of a 13-demethyl retinal bacteriorhodopsin (13-demethyl BR) film in gelatin matrix were investigated and compared to those of a native bacteriorhodopsin (BRWT) film. A two-wave mixing experiment was performed to study the self-diffraction efficiency of the samples. The rise and the decay of the grating in the 13-demethyl BR film was measured. The film is relatively slow enabling the recording of simultaneous gratings. Phase conjugate reflectivity was measured by a four-wave mixing experiment. Diffraction efficiency and phase conjugate reflectivity of the 13-demethyl BR film were observed to be comparable to those of the BRWT film.

Study on the Long Lifetime of the M State in Chemically Modified Bacteriorhodopsin Film

The M-state lifetime of bacteriorhodopsin (BR) could be significantly prolonged by using diaza-15-crown-5 as a chemical additive in BR−PVA films. With increasing additive content, the decay of the ...

Secure optical memory system with polarization encryption

A novel secure holographic memory system with polarization encoding is proposed. Two-dimensional original data are encoded as a two-dimensional polarization distribution. The polarization state at each pixel is scrambled by a mask that changes the polarization state into a random state. The mask can rotate the direction of the principal axes of the elliptically polarized light and can change the phase retardation at each pixel. The light with the random polarization state is stored as a hologram that can produce the vector phase-conjugate beam. In the decryption the vector phase-conjugation readout can recover the original polarization state by use of the same mask used in the encryption. Experimental results of encryption and decryption with a bacteriorhodopsin film are presented.

Infrared emission from photoexcited bacteriorhodopsin: studies by Fourier transform infrared spectroscopy

In the present work, using Fourier transform-infrared (FT-IR) technique we were able to register the infrared emission from a wet film of bacteriorhodopsin (bR) under continuous illumination with visible light (from a 100-W Xenon lamp) at room temperature. Emitted radiation is not induced by temperature rise, it has a discrete spectrum in the infrared range from 400 up to 4000cm−1. There are the bands relating to a retinelidene chromophore as well as to a protein matrix. By comparing these results with the resonance Raman and IR-absorption data the majority of stretching vibrations can be identified. The agreement in the frequency of bands assigned to the chromophore of bR is very good, whereas the difference occurs in the intensity distribution among the characteristic bands. It was found that the IR-emission spectra displayed two CC stretching frequencies at 1528 and 1516cm−1 attributed to the parent, bR568, and K610-intermediate states, respectively, whose intensity strongly depended on a varying of a wavelength of the incident light. The data presented here give new spectral information on the molecular processes occurring in the bR molecule during optical excitation.

Photoelectric conversion of bacteriorhodopsin films fabricated by self-assembly technique

The photoelectric response characteristics of bacteriorhodopsin (bR) thin films fabricated by self-assembly (SA) technique were presented. Self-assembled monolayers (SAMs) of 11-mercaptoundecanoic acid (11-MUA) on gold substrate were used as a template for the adsorption of bR. Using poly- l-lysine (PL), as a bridging molecule for bR adsorption onto SAMs of 11-MUA, bR thin films were fabricated. The photoelectric conversion of the prepared bR thin films was investigated.

Processing of medical images using real-time optical Fourier processing.

Optical image processing techniques are inherently fast in view of parallel processing. A self-adaptive optical Fourier processing system using photoinduced dichroism in a bacteriorhodopsin film was experimentally demonstrated for medical image processing. Application of this powerful analog all-optical interactive technique for cancer diagnostics is illustrated with two mammograms and a Pap smear. Microcalcification clusters buried in surrounding tissue showed up clearly in the processed image. By playing with one knob, which rotates the analyzer in the optical system, either the microcalcification clusters or the surrounding dense tissue can be selectively displayed. Bacteriorhodopsin films are stable up to 140 degrees C and environmentally friendly. As no interference is involved in the experiments, vibration isolation and even a coherent light source are not required. It may be possible to develop a low-cost rugged battery operated portable signal-enhancing magnifier.

Multi-exponentially Photoelectric Response of Bacteriorhodopsin

A thin oriented bacteriorhodopsin (bR) film is deposited on a stainlesssteel slide by the use of the electrophoretic sedimentation method. Ajunction is made with electrolyte gels having a counterelectrode toconstruct a bR-based photoelectric detector. The photoelectric responsesignal to a 10 ns laser pulse is measured. A theory on the photoelectrickinetics of bR is developed based on the concept of the charge displacementcurrent and the bR photocycle rate equations. Comparison between thetheoretical and experimental results proves that the bR photoelectricresponse to a short laser pulse is a multi-exponential process. Thedecay time constants and amplitudes of each exponential component areobtained by data fitting. PACS: 85. 60. Bt, 87. 15. Aa, 85. 65. +h

Vectorially oriented purple membrane: characterization by photocurrent measurement and polarized-Fourier transform infrared spectroscopy

Vectorially oriented membrane films containing bacteriorhodopsin (BR) on indium-tin-oxide (ITO) conductive glass (achieved by the electrophoretic sedimentation method), and randomly oriented films on ITO glass or CaF 2 plate (achieved by natural drying) have been characterized by using polarized Fourier-transform infrared (FTIR) spectroscopy and laser-induced photocurrent measurements. Vectorially oriented and randomly oriented membranes gave a similar average α-helical orientation of ∼30° with respect to normal membranes, as obtained from polarized FTIR spectra. Under pulsed laser excitation, two oppositely oriented BR films, with membrane surface either extracellular (EC) side or cytoplasmic (CP) side facing ITO (ITO/EC-CP vs. ITO/CP-EC), gave a photocurrent component pair, B1/B2, in a similar amplitude but with opposite polarity, whereas randomly oriented film simply shows very small B1/B2 signals. Thus, photocurrent measurement seems to be an effective and reliable way for the recognition of BR membrane orientation.

Generation of Faradaic Photocurrents at the Bacteriorhodopsin Film Electrodeposited on a Platinum Electrode

Generation of Faradaic Photocurrents at the Bacteriorhodopsin Film Electrodeposited on a Platinum Electrode

Multiplexed holograms in thick bacteriorhodopsin films for optical memory/interconnections

Multiplexed holograms recorded in purple-membraned bacteriorhodopsin (BR) films are investigated. Calculations of the reconstruction selectivity and crosstalk noise of BR-based holographic memory, along with experimental results, are presented. We also show that the properties of BR films can be effectively used for constructing holographic free-space optical interconnections that are reconfigurable in real time.

Bioelectronic Device Consisting of Bacteriorhodopsin for Pattern Recognition

Signals of a photoreceptor consisting of various configurations of bacteriorhodopsin (bR) and lipid films were analyzed to achieve the data (signal) transfer between molecular basic units without wiring. The signal shapes of the photoreceptor varied with different film fabrication conditions and film configurations. The possibility of data processing without pattern for pixelization in bioelectronic devices was presented.

Interferometric system for non-destructive testing based on large diameter bacteriorhodopsin films

A system for holographic interferometry using bacteriorhodopsin films as an erasable optical recording medium is presented. Bacteriorhodopsin is a photochromic protein found in archaebacteria. Bacteriorhodopsin films with an aperture of 90×90 mm are used for high-resolution lensless recording (5000 lines/mm). The holograms are recorded in reflection-type geometry in order to achieve a compact design. A frequency-doubled Nd : YVO 4 laser, emitting at 532 nm, is used for recording and incoherent blue light is employed for photochemical erasure. The system is suitable for a variety of different interferometric techniques like double-exposure, time-averaging and real-time interferometry. As an example for the application of the BR-based non-destructive testing system the inspection of ceramic motor valves, made from silicone nitride (Si 3N 4), under mechanical load is reported.

Kinetic Optimization of Bacteriorhodopsin Films for Holographic Interferometry

The M-lifetime of bacteriorhodopsin films for optical recording is a key parameter in obtaining a high light sensitivity, a high contrast ratio, and a high contrast decay time. An increase of the M-lifetime causes a proportional reduction of the light intensity required for optical applications. In bacteriorhodopsin variants such as BR-D96N, the M-lifetime can be tuned over several orders of magnitude by simply changing the pH value with respect to the proton availability in the matrix of the films. At low humidities, the proton transport steps linked to the photocycle limit the overall kinetics. A proton-diffusion-limited, two-state model (PDL2 model) for bacteriorhodopsin is introduced which allows us to model mathematically the optical excitation and thermal relaxation processes for both high and low humidities in bacteriorhodopsin films. Films containing wildtype bacteriorhodopsin and the variant D96N are compared in dependence on the pH value and the relative humidity at 20 °C. Of the investigated materials, only BR films containing BR-D96N can be used for recording at low light levels of 100 μW/cm2. In a holographic interferometry experimenta typical application where a high light sensitivity is a key issueit is demonstrated to what high extent the water content in the films affects their suitability for recording at low light levels. Kinetically optimized bacteriorhodopsin films yield a more-than-30-fold improvement of sensitivity in holographic interferometry compared to dry bacteriorhodopsin films.

Phase-modulated beams technique for thin photorefractive films characterization

The phase-modulated beams technique is developed for nonlinear thin photorefractive films characterization. In the Raman–Nath diffraction approximation, the formulas are deduced, allowing us to measure the amplitude of phase grating recorded in a film and its nonlinear refractive index n2. The method is applied for studying Langmuir–Blodgett multilayer thin (∼0.6 μm) films of Bacteriorhodopsin at wavelength 633 nm.