ARTICLE IN PRESS

Radiation Physics and Chemistry 78 (2009) 1071–1075

Contents lists available at ScienceDirect

Radiation Physics and Chemistry

0969-80

doi:10.1

� Corr

E-m

journal homepage: www.elsevier.com/locate/radphyschem

Sugar nanowires based on cyclodextrin prepared by single particlenanofabrication technique

Shogo Watanabe a, Atsushi Asano a, Shu Seki a,�, Masaki Sugimoto b, Masahito Yoshikawa b,Seiichi Tagawac, Satoshi Tsukuda d, Shun-Ichiro Tanaka d

a Division of Applied Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japanb Japan Atomic Energy Agency, Takasaki Advanced Radiation Research Institute, 1233 Watanuki-machi, Takasaki, Gunma 370-1292, Japanc The Institute of Scientific and Industrial Research, Osaka University, 8-1, Mihogaoka, Ibaraki, Osaka 567-0047, Japand Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai 980-8577, Japan

a r t i c l e i n f o

Keyword:

Ion beam

Cyclodextrin

Single particle

Nanowire

Cross-linking

6X/$ - see front matter & 2009 Elsevier Ltd. A

016/j.radphyschem.2009.06.019

esponding author. Tel.:+816 6879 4587; fax:

ail address: seki@chem.eng.osaka-u.ac.jp (S. S

a b s t r a c t

The direct formation of nanowires consisting of cyclodextrins by single particle nanofabrication

technique (SPNT) is investigated in the present paper. Substittuted cyclodextrin (CD) derivatives and

their composite with poly(4-bromostyrene) caused efficient cross-linking reaction upon irradiation, and

gave nanostructures by SPNT. Successful visualization of the nanostructures by atomic force microscopy

suggested drastic increase in the surface area of the materials based on CDs, leading to considerable

increase in the selective adsorption efficiency of the molecules fit to the size of the hydrophobic holes

of CDs.

& 2009 Elsevier Ltd. All rights reserved.

1. Introduction

The application of high-energy charged particles has extendedon many fields in recent years. The MeV order high-energycharged particle interaction with the matters have been used incancer radiotherapy (Wilson, 1946), breed improvement (Stadler,1928; Goodhead, 1992), etc., and their feasibility in materialsscience is also of considerable interests, where it has been knownas nuclear track fabrication (Fleisher et al., 1975; Spor, 1990; Priceand Walker, 1962). High-energy charged particle have often beencharacterized by their hard interaction with the organic materials,giving cylinder-like nanospace of ion tracks along the particletrajectories where reactive intermediates (ion radicals, neutralradicals, etc.) are produced non-homogeneously with extremelyhigh density (Price and Walker, 1962; Seki et al., 2001, 2004). Thechemical reactions within the limited nanospace are feasible toproduce one-dimensional (1-D) nanomaterials, and we havesuccessfully produced 1-D nanowires based on the cross-linkingreactions in the polymer thin films as target materials for high-energy charged particles (Seki et al., 2001, 2004, 2005; Seki andTagawa, 2007; Tsukuda et al., 2004, 2005, 2006). The presentnanoscaled negative tone imaging technique (single particlenanofabrication technique: SPNT) is applicable to a variety of

ll rights reserved.

+816 6879 4588.

eki).

polymeric materials with equally controlled sizes (length, thick-ness, number density, etc.).

Unlikely to the conventional e-beam or laser lithographictechnique (He and Cerrina, 1998; Mori et al., 1998), the SPNT isessentially free from the engineering factors originated from beamspot size, beam diffraction, depth of focus, optical alignment, etc.,because a 1-D nanowires is produced by corresponding high-energy single particle. Furthermore, the patterns of the nanowiresare realized as ‘‘negative’’ tone of cross-linked polymer molecules,thus the pattern size and shape are almost independent ofdevelopment procedures after the latent imaging by the presenttechnique.

Cyclodextrins (CDs) are one of cyclic oligosuccharidesthat several molecules of D-glucoses are combined each other byglucosidic linkage. Inside of circular configuration of CDs isa hydrophobic hole whose size is adapted for including othersmall molecules, so CDs indicates selective adsorbabilityfor hydrophobic molecules fitted the hole size and applied asabsorbents in the gas chromatograph, the high-performanceliquid chromatograph, etc. (Armstrong and Zukowski, 1994;Tavss et al., 1988). Nanostructures based on CDs are expectedto expand considerably the surface area of the materials, leadingto considerable increase in the adsorption efficiency of the targetmolecules.

In this paper, the nanostructures based on b-CDs and theirblends with polymers were formed by SPNT. The cross-linkingreactions in the ion tracks result in localized gelation, givingisolated b-CD nanowires on substrates. The radial sizes of

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S. Watanabe et al. / Radiation Physics and Chemistry 78 (2009) 1071–10751072

nanowires prepared by SPNT are also discussed quantitatively interms of cross-linking efficiency in detail.

2. Experimental

All reagents and chemicals were from Nacalai Tesque, Inc. orAldrich Chemical Co. and of the best commercial quality availableand used without further purification.

The substituted b-CD derivatives were synthesized along forScheme 1. Mono(6-tosyl)-b-CD was prepared as well-knownreaction of b-CD with p-toluenesulfonyl chloride in pyridine(Takahashi et al., 1984). Mono(6-folmyl)-b-CD was synthesizedfrom mono(6-tosyl)-b-CD with collidine in dimethyl sulfoxide(DMSO) (Yoon, 1995). Mono(6-epoxy)-b-CD was synthesized byCorey–Chaykovsky epoxidation (Corey and Chaykovsky, 1962).Mono(6-folmyl)-b-CD (86.3 mg) was dissolved in DMSO (20 mL)with trimethyl sulfonium iodide (46.7 mg) and sodium hydride(9.1 mg). After 4 h stirring, to quench sodium hydride, 2-propanol(40 mL) was added to the reaction mixture and stirred through3 h. 2-propanol was rejected under vacuum concentration. Theresulting solution was added drop wise to acetone (100 mL). Theflesh color precipitate (73.5 mg) filtrated under reduced pressure.Per(6-acetyl)-b-CD was synthesized as indicated below. b-CD(2.01 g) was dissolved in pyridine (8.0 mL) and acetic anhydride(8.0 mL). After 14 h, washed reaction mixture with sodiumhydrogen carbonate aqueous solution and brine, organiclayer was concentrated under reduced pressure to give whitepowder (3.42 g).

Mono(6-epoxy)-b-CD and b-CD were dissolved 1–5 wt% inwater, and spin-coated on Si substrate that had been treated withKOH aqueous solution over a period of 5 min. Per(6-acetyl)-b-CDand poly(4-bromostyrene) was dissolved 5 wt% in toluene, andspin-coated on Si substrate. The thickness of the films wasconfirmed by a Dektak 3st surface profiler. The films of the b-CDsand poly(4-bromostyrene) were irradiated by several kind of MeVorder charged particles from cyclotron accelerator at Japan AtomicEnergy Agency, Takasaki Advanced Radiation Research Institute.

p-TsCl

pyridine O

OH

OTs

O

OH

OTs

OH

OH

OH

O

7OH

OH

OH

O

7

OH

OH

CHO

OOH

OH

OH

O

6OH

OH

CHO

OOH

OH

OH

O

6

β-CD Mono

Mono(6-folmyl)-β-CD

S(Me3)NaH

DMS

β-CD

OO

OH

OH

OH

O

7OH

OH

OH

O

7

Per(ac

(CH3CO)2O

pyridine

Scheme 1. The synthesis of mono(6-epoxy)-b

The number of incident particles was controlled from 1�108 to1�1010 cm�2 to prevent overlapping of the particle trajectories.The irradiated films were developed directly in water or toluenefor 1–5 min. The sizes and shapes of the nanostructure formedalong particle trajectories were observed using a SPI-4000 atomicforce microscope (AFM) from Seiko Instruments Inc.

3. Results and discussion

Ion bombardment can release densely active intermediateswithin a cylindrical area along the passage of a single ion. Thecylindrical area, which deposited high-energy from the projectileion, is sometimes called an ‘‘ion track’’. These intermediates forman inhomogeneous spatial distribution in the ion track due to thevarious chemical reactions involved. Ion irradiation at low fluencewithout overlapping among ion tracks produces single ion eventsin target materials. The cross-linking reactions along the ion trackresult in the formation of a nanowire in thin films. A non-cross-linked area can be removed by development with organicsolvents, utilizing the change in solubility due to the gelation ofpolymers. The nanowires formed by ion bombardment can,therefore, be completely isolated on the substrate. However, theirradiation to the thin film of b-CD could not give isolatednanowires on the substrate, because the sufficient cross-links toform nanogel structures were not introduced within each iontrack along the projectile ions.

The radiation sensitivity of polymers, such as G values (numberof reactions per 100 eV of absorbed dose), have been studiedextensively for many polymers and types of radiation. The G

values are strongly depended on the molecular structures anddominate the cross-linking reaction caused by the radiations. Thespecific properties of ion beams have been characterized by thelinear energy transfer (LET), given by the energy deposition of anincident particle per unit length. The ion track radius is also animportant parameter in such reactions, reflecting the local spatialdistribution of energy deposited by an incident ion and influen-cing the character of subsequent chemical reactions. Thus,

HO

OH

OH

OH

O

6HO

OH

OH

OH

O

6

OH

OH OOH

OH

OH

O

6

O

OH

OH OOH

OH

OH

O

6

O

collidine

DMSO

(6-tosyl)-β-CD

+ I-

O

Mono(6-epoxy)-β-CD

OAc

Ac

OAc

O

7OAc

Ac

OAc

O

7

etyl)-β-CD

-CD and per(6-acetyl)-b-CD from b-CD.

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deposited energy density and cross-linking efficiency are veryimportant factors for formation of the nanogel structures in theion track.

In order to increase the efficiency of cross-linking reactions inb-CD, mono(6-epoxy)-b-CD was designed (Scheme 1), and320 MeV Ru ion beam was irradiated to the thin film of mono(6-epoxy)-b-CD . After the development procedure, isolated nano-dots were observed on the substrate by AEM measurement as

500nm

Fig. 1. AFM micrographs of nanodots based on mono(6-epoxy)-b-CD produced by SPNT.

thick after irradiation of 320 MeV Ru ion beam at fluence of 5.0�108 ions cm�2.

250nm

1μm

Fig. 2. AFM micrographs of nanowires based on the blended polymer of per(6-acetyl)-bthe blended polymer at 200 nm thick after irradiation of 450 MeV Xe ion beams at the

shown in Fig. 1. The thickness of the initial target film no longerreflects the length of the nanostructures, suggesting theconsiderable fragmentation of the nanowires occurs during thedevelopment procedure because of the slime nature and the lowmechanical strength of cross-linked mono(6-epoxy)-b-CDaggregates. In order to increase the tolerance for thefragmentation, per(6-acetyl)-b-CD and poly(4-bromostyrene)(PBrS) with high cross-linking efficiency were blended and spin-

1μm

Images (a)–(b) were observed in the thin films of mono(6-epoxy)-b-CD at �100 nm

500nm

2μm

-CD and PBrS produced by SPNT. Images (a)–(d) were observed in the thin films of

fluence of 3.0�109 ions cm�2.

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coated on the Si substrate. High-energy particles penetrating intothin film of the blend polymer (PBrS–b-CD) promote effectivelycross-linking reaction along the trajectories. The developmentprocedure isolated the nanowires on the substrate as shown inFig. 2. All nanowires are no longer standing, collapsed onto on thesubstrate observed as the 2-D images. As a control, the nanowiresof only PBrS is shown in Fig. 3. The size (especially radius of crosssection) of nanowires was depended on cross-linking efficiency ofsample materials with high quantitative correlation (Seki et al.,2004). The radial dose distribution (rE(r) eV nm�3) in an ion trackis given as a function of radial distance from a particle trajectory(r nm) by the following equation:

rEðrÞ ¼LET

22pr2 ln

e1=2rp

rc

� �� ��1

ð1Þ

where LET (eV nm�1) is the averaged energy deposition of theincident particle per unit length along the trajectory, and rc and rp

the radii of the core and penumbra areas, defined from theequation theorem of collisions of charged particles with matter(Magee and Chattarjee, 1987). The gelation of the polymermaterials (one cross-linking point per macromolecule) allowsthe derivation of energy density (rcr eV nm�3) at the boundary ofan ion track as a function of cross-linking efficiency (G(x)(100 eV)�1: number of cross-links induced by a radiation-deposited energy of 100 eV) (Seki et al., 2005)

rcr ¼100rA

GðxÞmNð2Þ

250nm

1μm

Fig. 3. AFM micrographs of nanowires based on PBrS produced by SPNT. Images (a)–(d)

Xe ion beams at the fluence of 3.0�109 ions cm�2.

where A is Avogadro’s number, m the mass of a monomer unit, r(g nm�3) the density of the polymer and N the degree ofpolymerization. Thus, the theoretical estimate of r is given bysubstitution of rE with rcr as follows: (Seki et al., 2004)

r2 ¼LETGðxÞmN

400prAln

e1=2rp

rc

� �� ��1

ð3Þ

The radii of the PBrS–b-CD and PBrS nanowires were determined4.4 and 5.9 nm by AFM measurement and calculation on theellipse model, respectively (Tsukuda et al., 2005). The values ofG(x) for PBrS–b-CD and PBrS were 0.22 and 0.39 by calculationusing Eq. (3), with the following empirical parameters:LET ¼ 9300 eV nm�1 (calculated for 450 MeV Xe ions in poly(4-bromostyrene) by the Monte Carlo simulation code ‘‘SRIM2003’’(Zieglar et al., 2003), r ¼ 1.28 g cm�3 andmN ¼ 6.5�104 g mol�1. The value of G(x) for PBrS were reportedas 0.30–1.6 (100 eV�1), which corresponded to calculated value(Burlant et al., 1962). The significant decrease on cross-linkingefficiency between PBrS–b-CD and PBrS indicates the blendedmaterials nanowires consisted essentially of well-blendedmaterial, and the included per(6-acetyl)-b-CD inhibits cross-linking reaction, resulting in reduced G value of PBrS–b-CD. Itwould be possible to control the radial size of nanowires bychanging the concentration of the mixtures. The lengths ofnanowires on each sample also corresponds to the initialthickness of the target polymer films, thus functional additionby blended b-CD into nanostructures and the precise size controlsby SPNT are effective for suger–polymer composite nanomaterials.

500nm

2μm

were observed in the thin films of PBrS at 200 nm thick after irradiation of 450 MeV

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4. Conclusions

On the basis of the strong dependence of the chemical yield ofcross-linking reaction on the molecular weight of the targetmaterials, nanowires were derived to represent the distribution ofcross-links in an ion track, and also clearly visualized by AFM. Thenanowires based on PBrS–b-CD were successfully formed andisolated on the substrate. The size (radius) of nanowires based onPBrS–b-CD were decreased compared with one of the originalPBrS because of decrease of the cross-linking efficiency (G values).The present results also indicate possibility to expand drasticallysurface area of materials, leading to efficiently adsorption forsensors by using CD nanowires.

Acknowledgements

This work was supported in part by a Grant-in-Aid forScientific Research from the Ministry of Education, Culture, Sports,Science and Technology in Japan.

Reference

Armstrong, D.W., Zukowski, J., 1994. Direct enantiomeric resolution of monoterpenehydrocarbons via reversed-phase high-performance liquid chromatography with ana-cyclodextrin bonded stationary phase. J. Chromatogr. A 666, 445–448.

Burlant, W., Neermann, J., Serment, V.J., 1962. g-radiation of p-substitutedpolystyrenes. J. Polym. Sci. 58, 491–500.

Corey, E.J., Chaykovsky, M., 1962. Dimetylsylfoxonium methylide. J. Am. Chem. Soc.84, 867–868.

Fleisher, R.L., Price, P.B., Walker, R.M., 1975. Nuclear Tracks in Solid. University ofCakifornia Press, Los Angeles.

Goodhead, D.T., 1992. Molecular and cell models of biological effects of heavy ionradiation. Radiat. Environ. Biophys. 34, 67–72.

He, D., Cerrina, F., 1998. Process dependence of roughness in a positive-tonechemically amplified resist. J. Vac. Sci. Technol. 16, 3748–3751.

Magee, J.L., Chattarjee, A., 1987. In: Freeman, G.R. (Ed.), Kinetics of Nonhomoge-neous Processes. Wiley, New York, pp. 171 (Chapter 4).

Mori, S., Morisawa, T., Matsuzawa, N., Kaimoto, Y., Endo, M., Matuo, T., Kuhara, K.,Sasago, M., 1998. Reduction of line edge roughness in the top surface imagingprocess. J. Vac. Sci. Technol. 16, 3739–3743.

Price, P.B., Walker, R.M., 1962. Observation of fossil particle tracks in natural micas.Nature 196, 732–733.

Seki, S., Maeda, K., Tagawa, S., Kudoh, H., Sugimoto, M., Morita, Y., Shibata, H., 2001.Formation of nanowires along ion trajectories in Si backbone polymers. Adv.Mater. 13, 1663–1665.

Seki, S., Tsukuda, S., Maeda, K., Matsui, Y., Saeki, A., Tagawa, S., 2004.Inhomogeneous distribution of crosslinks in ion tracks in polystyrene andpolysilanes. Phys. Rev. B 70, 144203–144218.

Seki, S., Tsukuda, S., Maeda, K., Tagawa, S., Shibata, H., Sugimoto, M., Jimbo, K.,Hashitomi, I., Koyama, A., 2005. Effects of backbone configuration ofpolysilanes on nanoscale structures formed by single-particle nanofabricationtechnique. Macromolecules 38, 10164–10170.

Seki, S., Tagawa, S., 2007. Optoelectronic properties and nanostructure formation ofs-conjugated polymers. Polym. J. 39, 277–293.

Spor, R., 1990. Ion Tracks and Microtechnology. Vieweg, Braun-schweig.Stadler, L.J., 1928. Mutations in barley induced by X-rays and radium. Science 68,

186–187.Takahashi, K., Hattori, K., Toda, F., 1984. Monotosylated a- and b-cyclodextrins

prepared in an alkaline aqueous solution. Tetrahedron Lett. 25, 3331.Tavss, E.A., Wiet, S.G., Robinson, R.S., Santalucia, J., Carroll, D.L., 1988. Flavor

characterization of dentifrices using kinetic headspace gas chromatography. J.Chromatogr. 438, 273–280.

Tsukuda, S., Seki, S., Tagawa, S., Sugimoto, M., Idesaki, A., Tanaka, S., Ohshima, A.,2004. Fabrication of nano-wires using high-energy ion beams. J. Phys. Chem.108, 3407–3409.

Tsukuda, S., Seki, S., Sugimoto, M., Tagawa, S., 2005. Nanowires with controlledsizes formed by single ion track reactions in polymers. Appl. Phys. Lett. 87,233119(1)–233119(3).

Tsukuda, S., Seki, S., Sugimoto, M., Tagawa, S., 2006. customized morphologies ofself-condensed multi-segment polymer nanowires. J. Phys. Chem. B 110,19319–19322.

Wilson, 1946. Radiological use of fast protons. Radiology 47, 487–491.Zieglar, J.F., Biersack, J.P., Littmark, U., 2003. The Stopping and Range of Ions in

Solids. Pergamon Press, New York.