박테리오로돕신과 스피로피란으로 구성된 하드웨어 타입의 광신호 증폭기

민 준홍, 최 현구, 한 건국, 최 정우, 이 원홍

서강대학교 화학공학과

Hardware-type Photo Signal Enhancer Consisting of

Bacteriorhodopsin and Spiropyran

Junhong Min, Hyun-Goo Choi, Keon-Kook Han, Jeong-Woo Choi, Won Hong Lee

Department of Chemical Engineering, Sogang University

Introduction

In the biological molecules, membrane protein that acts as a light-driven proton pump has been reported[1,2]. Various artificial molecular devices have been fabricated by mimicking the electron transfer function of proteins[3,4] or photochromic function of biological membrane [3,4].

In this study, hardware-type photo signal enhancer consisting of bacteriorhodopsin and spiropyran films is constructed to enhance the ratio of output photo induced electrical response generated by transmitted light, which can be applied to the construction of hardware-type photo signal enhancer for the extraction for the desired image.

Spiropyran has been widely studied due to its photochromic properties that can be applied to optical memory[5,6]. The effects of film structures on the photochromic properties have been studied and multi-frequency optical memory using the spiropyran state and J-aggregated state, which show the different absorption spectrum, was proposed [7]. In this study, The spiropyran films are applied to enhance the intensity ratio of the transmitted light, in comparison with that of input light, by irradiating two input lights of the different light intensity onto the films.

Bacteriorhodopsin Langmuir-Blodgett films are used to generate the photo induced electrical response depending on the light transmitted through the spiropyran films. The proposed hardware-type photo signal enhancer consisting of spiropyran and bacteriorhodopsin is investigated with respect to enhancement efficiency.

Materials and Methods

Materials

Bacteriorhodopsin was purchased from Sigma Co.(St. Louis, USA) and the samples used in these experiments were prepared from an aqueous suspension of bacteriorhodopsin. ITO glass (surface resistance〈 30□) obtained from Samsung Display Device Co.(Korea) was etched by HCl solution with Zn as a catalyst. 6-nitro spiropyran is synthesized in our laboratory.

The measuring System of Photo induced electrical Response of Hardware-type Photo Signal Enhancer

The experimental system was composed of a low-noise current preamplifier (Stanford Research System, USA), an amplifier(B&H, DC10000H2O, USA) and an oscilloscope(Gould 200MHz, USA). The 150 Xenon arc lamp (Oriel Co., USA) with an optical filters (450, 500, 550, 600 and 650nm) was used as a light source.

Figure1.	Scheme of measuring system of photo induced electrical response of        hardware-type photo signal enhancer

1. Al electrode, 2. Bacteriorhodopsin Langmuir-Blodgett films, 3. ITO layers,

4. Glass, 5. 6-nitro spiropyran film, 6. Low-noise current amplifier,

7. Power amplifier, 8. Oscilloscope, 9. 150W Xenon lamp set

Construction of Photo Signal Enhancer Composed of ITO/Bacteriorhodopsin/Al

The spiropyran was deposited onto the one side of glass slide by the spin coating method , and then bacteriorhodopsin Langmuir-Blodgett films were deposited onto the other side of glass on which ITO were pre-deposited. Prior to deposition of the upper electrode (Al), 6 monolayers of viologen were deposited onto the surface of bacteriorhodopsin films to prevent the denaturation of bacteriorhodopsin molecules during the deposition process of Al. The light was irradiated onto the spiropyran side at first, and then the transmitted light through the spiropyran layers reached to bacteriorhodopsin Langmuir-Blodgett films via the glass plate. The photocurrent of bacteriorhodopsin was generated proportionally to the transmitted light intensity

Results and discussion

The absorbance of 6-nitro spiropyran film in the region of visible light was changed by the irradiation of UV light as described previously. The photomerocyance, the coloration state of spiropyran by UV light, has the absorbance peak in the region of visible light which can be changed by the irradiation of visible light irradiation.      This absorbance peak decreases proportionally to the irradiated visible light intensity and time. If the two input lights of different light intensity (I10 / I20) irradiate on the photomerocyanine films, the absorbance of two parts irradiated by different light intensity is obtained as different values. By Lambert-Beer's law, the ratio of the transmitted light becomes,

I1 / I2 = I10 / I20 e (A2 - A1)

where, I : the intensity of light,

A : absorbance,

subscript o : input light

If I10 / I20 is larger than unity, (A2 - A1) becomes larger than zero due to the photochromic property of photomerocyanine. Due to  e (A2 - A1), the intensity ratio of transmitted light (I1 / I2) is larger than that of input light (I10 / I20). Thus, the increment of intensity ratio of transmitted light in comparison with that of input light can be obtained through the photomerocyanine films with irradiation time when two input lights of the different light intensities are irradiated onto the films.     Enhancement efficiency is defined as (I1 / I2) = (I10 / I20)×100.

Hardware-type photo signal enhancer composed of bacteriorhodopsin and 6-nitro spiropyran was fabricated for the enhancement of the intensity ratio of two input lights. The photo induced electrical response generated by bacteriorhodopsin was proportional to the light intensity change.

In the constructed hardware-type photo signal enhancer, the increment of the intensity ratio of transmitted light in comparison with that of input light was obtained when two input lights of the different light intensity were irradiated onto the films.

As shown in Figure 2, the enhancement efficiency was maximized after about 40min with the 2:1 ratio of input light intensities. The efficiency of enhancement was found to be a function to be a function of absorbance difference and irradiation time.

The enhancement efficiency of the constructed hardware-type photo signal enhancer consisting of spiropyran-bacteriorhodopsin films was about 25% with 40min of the enhancing time of two input lights(I10/ I20=2/1).

To increase the enhancement efficiency and to reduce the its time, two 6-nitro spiropyran was applied. so the enhancement efficiency of hardware-type photo signal enhancer with two spiropyran films was about 40% with 40min of enhancement efficiency.

Figure 3 showed the enhancing ratio with respect to the various input the signal-to-noise. The enhancing efficiency(about 25%) was not changed with respect to various input lights ratio.

But, the time for the maximize of enhancement efficiency was reduced as the ratio of input lights was increased. So, the control of the enhancing capability of constructed photo signal enhancer make if possible to optimize enhancement efficiency of light intensity as the characteristics of the system.

Figure 2                               Figure 3

Figure 2. The enhancement efficiency by hardware-type photo signal enhancer with two noise filter

Figure 3. The enhancement of intensity ratio of input lights with various intensities by hardware-type photo signal enhancer

References

[1] T. Miyasaka & K. Koyama, Rectified photocurrents from purple membrane Langmuir-Blodgett films at the electrode-electrolyte interface, Thin Solid Films, 210/211, pp 146-149, (1992).

[2] E. Racker & W. Stoeckenius, Reconstitution of Purple Membrane Vesicles Catalyzing Light-driven Proton Uptake and Adenosine Triphosphate Formation. The Journal of Biological Chemistry, 25, pp 662-663 (1974).

[3] T. Miyasaka & K. Koyama & I. Itoh, quantum Conversion and Image Detection by a Bacteriorhodopsin-Based Artificial Photoreceptors. Science, 255, pp 342-344 (1922).

[4] T. Miyasaka & K. Koyama, Image sensing and processing by a bacteriorhodopsin-based artificial photoreceptor. Appl. Opt., 32, pp 6371-6378 (1993).

[5] M. Morin, R. M. Leblanc, & I. Gruda, Spectral and photochromic properties of two long-chain spiropyranindoline monolayers at the air-solid interface. Can. J. Chem, 58, pp 2038-2043 (1980).

[6] A. Miyata, Y. Unuma & Y. Higashigaki, Optical Properties and Molecular Orientation of Aggregates in Langmuir-Blodgett Films of a Long-Chain Spiropyran. The chemical society of Japan, 66, pp 993-998 (1993)

[7] E. Ando, M.-A. Suzuki, K. Moriyama and K. Morimoto, Molecular arrangement of photochromic spiropyran on a subphase. Thin Solid Films, 178, pp 103-108 (1988)