신경망기능을 모방한 생물전자소자에서의 신호처리기술

민 준홍, 최 현구*, 오병근*, 최정우*, 이원홍*, 백세환

고려대학교 생명공학원

서강대학교 화학공학과*

Data Processing in Bioelectronics Mimicking Neural Network

Junhong Min, Hyun-Goo Choi*, Byung-Keun Oh*, Jeong-Woo Choi*,

Won Hong Lee*, Se-Hwan Paek

Graduate School of Biotechnology, Korea University

Department of Chemical Engineering, Sogang University*

Introduction

Silicon integrating technology has been developed rapidly in the prospect of device integrity and memory capacity [1,2]. However, in order to open a new field of electronic devices, it is important to study the excellent information-processing functions, which living organisms inherently have, including learning, memorizing, and pattern recognition. The development of new information-processing devices by utilizing the information-processing functions of living organisms and by using the molecular organization have been emerged. Various artificial molecular devices have been fabricated by mimicking specific material recognition function in many enzymes or photoelectronic function of biological membrane. The most outstanding characteristics of bioelectronic device is the specific functionality of the biomolecules which can act as a basic unit of electronic devices. But, in order to achieve these characteristics, the molecular wiring is needed for the data or information transfer from molecule to molecule. The new concept, such as DNA molecular wiring, has been introduced to solve the interconnection problem. But, the molecular wiring contains sophisticated techniques and high process cost. So, the simple concept for the data transfer and processing in bioelectronic device are required.

In this paper, signals of photoreceptor consisting of bacteriorhodopsin were processed by mimicking the functions of neural network (threshold, weighted summation, plasticity) to achieve the data (signal) transfer between molecular basic units without wiring. The mimicking of neural network is achieved by comparing the signal shapes varied with different film fabrication conditions and different film configurations. The possibility of data processing without wiring for interconnection in bioelectronic devices is presented in this paper.

Principles

The total signal from a photoreceptor consisting of bacteriorhodopsin films is the result of the summation of signals from individual bacteriorhodopsin molecules. If molecules are deposited with different conditions, the signal from each molecule is different from one another, and the signal from a molecule in certain region can be extracted from the total signal of a photoreceptor because the signal shape of bacteriorhodopsin varies with deposition conditions and environmental conditions due to the diffusion effect of H+ ion. The separation of individual signals of specific regions in a photoreceptor from total signals is, therefore, possible if a photoreceptor is fabricated by various deposition conditions and has different film configurations.

Figure . The principles of data process by mimicking neural network

Figure . The three types of film configuration (a) bacteriorhodopsin, (b) bacteriorhodopsin/viologen, (c) viologen/bacteriorhodopsin, and schematic photoreceptor consisting of three types of film configuration.

Experimentals

Bacteriorhodopsin was deposited by Langmuir-Blodgett technique with various configurations. The three types of film configurations were selected as shown in Figure 2. The layer of viologen was used as a diffusion limitation layer for H+ ion. The experimental setup for signal detection is composed of a low-noise current amplifier(Stanford Research System, USA), a power amplifier (B&H, USA) and an oscilloscope (H.P., USA). The all experiments were performed in an electrolyte solution (1.1M KCl) with Pt electrode as counter electrode.

Results and Discussion

Viologen and the bacteriorhodopsin are deposited by Langmuir-Blodgett technique. The surface of each LB layer was investigated by AFM (Atomic Force Microscope) as shown in Figure 3. The viologen molecules are aggregated and the size of aggregates are increased as time course. (Figure 3(a)). The patches of purple membrane containing bacteriorhodopsin are deposited on ITO surface as shown in Figure 3(b). The orientation of patch of bacteriorhodopsin is somewhat uniform in small range but not uniform factually.

(a)

(b)

Figure 3. The AFM Topologies of (a) viologen monolayer

and (b) bacteriorhodopsin monolayer

Figure 4 represents the various signals of the photoreceptor fabricated with the various configurations. Signal in Figure 4(a) is the result of configuration  Figure 2(a) (Figure 4(b) and Figure 4(c) correspond to Figure 2(b) and Figure 2(c), respectively). As shown in Figure 4, the typical signal (differential response) of bacteriorhodopsin to continuous illumination is occurred in the photoreceptor containing the only bacteriorhodopsin layer. But, small peak and large inverse signal are shown in the signal of the photoreceptor consisting bacteriorhodopsin and viologen. So, the great difference of signal shape is shown as layer configuration of a photoreceptor varies. If one photoreceptor has three configurations mentioned above, the photoreceptor have several signal shapes, ranging from 7(proper subset, 2n-1, n=3) to infinite. Typical 7 signal types of one photoreceptor consisting of three different film configurations are shown in Figure 4(d). With the decreasing parts, A(0.5-1.5s), and end parts, B(8-9s), signals can be distinguished from one another. So, the output signal of a photoreceptor can express a portion of each pixel

(a)

(b)

(c)

(d)

Figure 4. The signal of a photoreceptor consisting of

(a) only bacteriorhodopsin, (b) bacteriorhodopsin/viologen,

(c) viologen/bacteriorhodopsin, (d) three configurations (a, b, c)

Acknowledgment

This work was supported by the grants from the Korean Research Foundation.

References

[1] Miyasaka, T., Koyama, K. and Itoh, I.: Science, 225, 342(1992) .

[2] Min, J., Choi, H.-G., Choi, J.-W., Lee, W.H., and Kim, U.R.: Thin Solid Films, 327-329, 698(1998)