Electronic Properties of DNA-Surfactant Complex and Its application to DNA-based Bio-organic field effect transistor memory

Lijuan Liang 1, Tomoyashi Yukimoto1, Sei Uemura2,

Toshihide Kamata2, Kazuki Nakamura1, Norihisa Kobayashi1* 1Department of image & Materials science, Graduate School of Advanced Integration Science,

Chiba University, 1-33 Yayoi-chi, Inage-ku, Chiba, 263-8522, Japan; 2Flexible Electronics Research Center, National Institute of Advanced Industrial Science and Technology, Central 5, 1-1-1 Higashi,

Tsukuba, Ibaraki, 305-8565, Japan.

ABSTRACT

The bio-organic thin film transistor (BiOTFT) with the DNA and DNA-surfactant complex as a dielectric layer shows memory function. In order to investigate the effect of surfactant structure on the OTFT memory device performance, different kinds of surfactant were introduced. Cetyltrimethylammonium chloride (CTMA), Lauroylcholine chloride (Lau) or Octadecyltrimethylammonium chloride (OTMA) as the cationic surfactant was mixed with DNA to prepare the DNA complex through the electrostatic interaction. In addition, the different molecular weight DNA also has been studied to analyze the effect of DNA chain length on the performance of the physical property. Many kinds of methods including UV-vis, Circular dichiroism (CD), I-V characteristic and atomic force microscope (AFM) have been applied to analyze the property of DNA complex. In conclusion, all of DNA complex with CTMA, OTMA and Lau were revealed to work as the bio-organic thin film transistor memory, and the device fabricated by Lau has the highest ON current and showed better device performance.

Keywords: Deoxyribonucleic acid, cationic surfactant, physical property, hysteresis, organic transistors

1. INTRODUCTION In recent years, the biopolymers have attracted attention for their possible application for photonic and electronic

materials because of the highly ordered structure and unique properties. Furthermore, natural biomaterials are a renewable resource and are inherently biodegradable, which would open up widely application in large area as the environmentally-friendly materials1-4. For instance, organic field effect transistors, optical amplifiers5, conductive, semiconductive nanowires6, and nonlinear optical electro-optic modulators have been fabricated from DNA-based biopolymers. Such devices have demonstrated high performance that exceeds that of state-of-the-art devices made with currently available organic based materials7-11. In our study, we have already reported the organic light-emitting diodes fabricated with DNA as a template of charge transport materials and light-emitting materials12, 13.

The natured and purified DNA was soluble only in water, the resulting film are too water sensitive and have insufficient mechanical strength. Further, DNA is cationic polyelectrolyte which normally contains sodium ions as counter cations. We already reported the BiOTFT memory device prepared by natural DNA as the gate dielectric shows poor device performance such as the high OFF current because the existence of the sodium ions probably contributed ion conduction. Okahata et al reported preparation of DNA-cetyltrimethylammonium, CTMA complex which was soluble in organic solvent and was effective to reduce the mobility of counter ions14. After this novel finding, in order to exclude the influence of the sodium ions of DNA and to prepare the high quality thin films, researchers utilized the DNA surfactant complex for the application of electronic devices including OTFT. We have also reported the improvement of BiOTFT memory properties by excluding movable ions such as sodium cations with Lau surfactants15.

In this study, in order to investigate the influence of surfactant structure on BiOTFT device performance, the physicochemical properties of various DNA surfactants complex in solution and film state have been studied. Further, BiOTFT device performance such as transfer property has also been examined and the possible explanation of the device performance has been discussed.

* koban@faculty.chiba-u.jp; phone +81-43-290-3458; fax +81-43-290-3490; http://photo-m.tp.chiba-u.jp/i-poly/

Invited Paper

Nanobiosystems: Processing, Characterization, and Applications V, edited by Norihisa Kobayashi, Fahima Ouchen, Ileana Rau, Proc. of SPIE Vol. 8464, 846406

2012 SPIE CCC code: 0277-786X/12/$18 doi: 10.1117/12.932267

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2. EXPERIMENT SECTION 2.1 Materials

The sodium salts of DNA (bp = ca. 100 and 10000) were provided by Prof. Ogata and Nippon Chemical Feed Co.,Ltd. Pentacene(98% purity) were bought from Naad Co., Ltd. Lauroylcholine chloride(Lau), OTMA(98% purity), butanol and CTMA(98% purity) were purchased from Tokyo Chemical Industry Co., Ltd.

2.2 Preparation of DNA surfactant complex

DNALau was prepared by adding 10 mmol/L of DNA (concentration of the phosphate group) aqueous solution into 10 mmol/L of the lauroylcholine chloride aqueous solution, and then the precipitate were filtered and thoroughly washed with ultrapure water and then dried in vacuo at 50 for at least 24 hours. A write powder was obtained as a yield of 98% and also DNA-OTMA, DNA-CTMA were prepared through the same preparation process with the same yield.

2.3 Preparation of DNA and DNA surfactant complex solution and film

The sodium salts of DNA were dissolved in ultrapure deionized water with the concentration equals to 100 mmol/L. The 100 mmol/L DNA-Lau, 100 mmol/L DNA-OTMA or 100 mmol/L DNA-CTMA complexes was dissolved in butanol. The solution thus obtained was spin-coated on ITO glass substrates, and the films were dried for at least 12 h in vacuo. The thicknesses of the DNA film was about 6 m and the DNA surfactant complex films were approximately 2 m respectively.

2.4 The preparation of OTFT memory

OTFT memory devices were fabricated by depositing a pentacene layer (film thickness =50 nm) as an active layer at a pressure of 210-3 Pa and an evaporation rate of 0.20.4s-1 on the ITO/DNA or ITO/DNA complex film. Au as the source and drain electrodes (W/L=5 mm /20 m) was deposited by vacuum evaporation on this pentacene film. The chemical structure of Lau and OTMA, CTMA serving as surfactant to prepare the DNA based gate dielectric are shown in Fig. 1 (a), (b), (c) respectively. BiOTFT structure using a top contact and gate bottom geometry is schematically depicted in Fig. 1(d).

Figure 1. Chemical structure of (a) Lau. (b) OTMA. (c) CTMA. (d) Schematic of the top contact and bottom gate BiOTFT memory

2m DNA complex

G

50 nmP-type semiconductor S D

(a)

(b)

(c)

(d)

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1.0

0.8

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200 300Wavelength / nm

high DNA -Lau

high DNA -CTMAhigh DNA -OTMA

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low DNAICTMAlow DNAJOTMAlow DNA/Lau

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Wavelength / nm

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3. RESULTS AND DISCUSSION 3.1 UV absorption spectra of the DNA complex.

The UV absorption of DNA is an important property for determining whether - stacking of nucleobases occurs. The DNA double helix in aqueous solution has a specific absorption band from 220 nm to 300 nm with a max at 260 nm16. In order to compare the effect of different molecular weight of DNA with different cationic surfactant on the structural regularity, the UV-visible spectra have been measured.

The Figure 2 and Figure 3 show the UV-visible spectra of DNA-Lau, DNA-OTMA and DNA-CTMA in butanol solutions. It was clear that both the high (10 kbps) and low (100 bps) molecular length with different DNA complex have the same maximum absorption wavelength at 260 nm, which was assigned as the characteristic absorption of the nucleobases in DNA. And the molecular length had no relationship with the UV spectral. The - stacking of nucleobases of the DNA did not change when the molecular weight altered, indicating that both the high and low molecule DNA retained the double helix structure after the ion exchange reaction in the butanol solution.

Figure 2. UV-vis spectra of DNA complex solution with high molecular weight.

Figure 3. UV-vis spectra of DNA complex solution with low molecular weight DNA

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high DNA -Lau '

high DNA -CTMA -high DNA -OTMA

-4200 300

Wavelength / nm

400

6

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-2

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low DNA/CTMAlow DNA/OTMAlow DNA/Lau

200 300 400

Wavelength / nm

3.2 CD spectra of the DNA complex

CD analysis is one of the most useful techniques for probing the conformation of DNA complex in many kinds of solutions, in gels, films as well as fibers17. In order to compare the different molecular weight of DNA with different surfactant and to analyze its effect on the double helix structure, both the solution and the film have been investigated.

Figure 5. CD spectra of DNA complex solution with low molecular weight DNA

Figure 4. CD spectra of DNA complex solution with high molecular weight DNA

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86

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6200 300

low DNA -Lau

low DNA -CTMAlow DNA -OTMA

Wavelength / nm

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o

low DNAhigh DNA

0 2 4 6 8 10Voltage / V

The Figure 4, Figure 5 and Figure 6 show the CD spectra of the solution and film state. All of the complexes either in butanol solution or in the film state showed positive and negative CD signals. In the case of the solution, a positive Cotton effect at about 280 nm and a negative Cotton effect at about 225 nm and 245 nm have been observed, which is similar in shape to natural DNA. Meanwhile, the A form of the DNA complexes in butanol solution appeared to be transformed to the B form in the film state. In addition, with the increase of the alkyl chains, the CD signal decreased, indicating that the decrease of structure regularity, it would be because the hydrophobic properties of the alkyl chain and steric hindrance between the long alkyl chains.

3.3 I-V properties of the DNA complex film

It is known that the resistivity of the DNA complex plays an important role in the property of the BiOTFT memory when using as the insulator layer. Therefore, it is necessary to evaluate the resistivity of the DNA complex. For comparison, the I-V characteristics of DNA alone with different chain length are also shown in Figure 7, 8 and Figure 9.

Figure 6. CD spectra of DNA complex film with low molecular weight DNA

Figure 7. I-V characteristics of ITO/high and low DNA /Au cells

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high DNA -Lauhigh DNA -CTMA

A high DNA -OTMA

400wIWW0 5

Voltage / V10

00

low DNA -Laulow DNA -CTMA

A low DNA -OTMA

!AAAA45 10

Voltage / V

From Figure 7, Figure 8 and Figure 9, they show that the resistivity of DNA complex increased significantly in comparison with DNA alone with either high or low chain length. It would be because the DNA which is one of the poly-anion could be interacted with cationic surfactant through the ion exchange reaction, leading to the decrease of the movable ions such as sodium ions and to the improvement of the resistivity. In addition, the Figure 8 and Figure 9 also show that with the increasing of the alkyl chains, the resistivity also increased, it was because the longer alkyl chains provided the higher proportion of the insulative alkyl chains in the DNA complex film, which would improve the insulating property. Besides, compared to the high molecular weight DNA, the low molecular weight DNA showed the better resistivity when the same surfactants were applied. This was due to the decrease of the carrier conductive pathway along the DNA chains when the length of DNA chain was short. In conclusion, the kinds of the surfactant and the chain length of the DNA have great effect on the resistivity of the film. The resistivity of the low molecular DNA-Lau, DNA-

Figure 8. I-V characteristics of ITO/high DNA /Au cells

Figure 9. I-V characteristics of ITO/ low DNA /Au cells

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