Real-time holographic imaging with a bacteriorhodopsin film

Photochromic polymer films based on a 14-F bacteriorhodopsin derivative

Spectral and kinetic characteristics were measured for polymer (gelatin) films based on 14-F bacteriorhodopsin (BR), both wild-type (WT) and D96N mutant, to study the peculiarities of photo-induced transformation of the samples. It was demonstrated earlier that incorporation of 14-F retinal into the apomembrane of both 14-F WT and 14-F D96N produces pigments with drastically different photo-induced behavior, regarding the formation and decay of a red-shifted species at 660 nm. However, similar fundamental differences between 14-F WT and 14-F D96N, if embedded into gelatin matrix, were not observed. Results are discussed in the frame of the relationship between the kinetic rates of two photo-induced processes that occur in suspensions and gelatin films of corresponding pigments. These experimental results can possibly be explained by the difference in kinetics for gelatin films and water suspensions. The main factor in altering the kinetics is the relative humidity of gelatin samples. Therefore, the effect of relative humidity on performance of 14-F BR gelatin films, both WT and D96N, was studied. A range of humidity has been defined for each pigment, in which spectral and kinetic characteristics were changed in the desired direction. It was shown that 14-F WT gelatin films may offer a technological advantage relative to those based on 14-F D96N.

Dynamic Holography in Bacteriorhodopsin/Gelatin Films: Effects of Light-Dark Adaptation at Different Humidity†

This work examines the kinetics of dynamic holography responses in light-adapted and dark-adapted bacteriorhodopsin (BR) films at different humidity. We have demonstrated that the kinetics of the diffraction efficiency in wild type BR films is quite different in dark-adapted and light-adapted samples. The holographic recording kinetics, which depends on the duration of incubation in the dark after light adaptation at different humidity values, was studied in depth. A specially designed miniature cell containing a BR film was mounted inside the holographic set up to allow controlled humidity changes over a broad range. The diffraction efficiency kinetics at humidity values of 96-99% were quite different from the kinetics at 60-93% humidity. We found that humidity values of 90-93% were most optimal for dynamic holography recording using a gelatin film containing BR. In agreement with a calculation of the wavelength-dependent changes of the refractive index for dark-adapted and light-adapted BR samples using the Kramers-Kronig relation, the maximum difference in the refractive index and thus in the diffraction efficiency for dark-adapted and light-adapted BR films takes place at 630 nm, close to the wavelength of the He-Ne laser used.

Dynamic properties of bacteriorhodopsin exposed to ultrashort light pulses

Bacteriorhodopsin (BR) in its metastable form was used for pulsed holographic recording at lambda~400nm . It is shown that the properties of BR are insensitive to changes in the writing light's pulse width. When holograms are recorded in the BR stable form (lambda~600 nm) , the sensitivity of the medium and the diffraction efficiency of those holograms are reduced proportionally to the decrease in the light's pulse width.

Study of nonlinear optical properties of multilayer Langmuir-Blodgett films containing bacteriorhodopsin

Multilayer oriented Langmuir-Blodgett films of bacteriorhodopsin were prepared and their nonlinear optical properties, including second harmonic generation and photoresponse at a two phase-modulated beams mixing, were investigated. The nonlinear component of refractive index of the films was measured.

Incoherent-to-coherent conversion and square-law transmission based on photoinduced birefringence in bacteriorhodopsin films

We review the main optical properties of bacteriorhodopsin that are relevant to its use as a spatial light modulator. A model is described for the transmittance of a film placed between crossed polarizers in which photoinduced birefringence occurs. We show when the transmittance is proportional to the write intensity. We use this property in a joint transform correlator for incoherent-to-coherent conversion and effective square-law modulation in the Fourier plane.

Optical and electrical characterization of bacteriorhodopsin films

The lifetime of the M-state of bacteriorhodopsin (BR) is increased by genetic and chemical modifications and by solubilizing purple membranes (PMs) with detergent. Chemically modified D96E films as well as D96N films, possess close to 100% bleaching efficiency which makes them attractive for use as image storage media. The mutant S35C has spectral and kinetic properties identical to the WT, both in aqueous suspensions and in films. This indicates that substitution of Ser-35 with Cys has an insignificant effect on the photocycling activity of BR. This substitution provides an attachment site that does not interfere with the function of BR. The magnitude of photocurrent transients generated by mutant BR proteins is used to measure the efficiency of the ground-to-M-state transitions.