AIMR Annual Review
Contents

2011 WPI-AIMR Main Events ………………………………………………………… 1
Award Information ………………………………………………………………….…. 2
List of Major Governmental Research Funds (As of August 1, 2011) ……………… 4
The Fourth Series of WPI-AIMR Joint Seminars FY 2011 …………………..….….. 6
Research Prospect
Winfried TEIZER …………….………………………………………………………. 15
Hongkai WU ……………………………….…………………………………………. 21
Kazue KURIHARA ………………………………………………………………….. 26
Tomokazu MATSUE ………………………………………………………………… 36
Naoki ASAO ………………………………………………………………………… 43
Shigemi MIZUKAMI ……………………………………………………................... 53
Global Intellectual Incubation and Integration Lab (GI3 lab) ………..…………… 63

2011 WPI-AIMR Main Events
Feb 21 WPI-AIMR is presented in Physics Today.
Mar 10 Dr. Khademhosseini was awarded "Sloan Research Fellowship"
Mar 10 Prof. M. Kawasaki (PI) will be awarded "8th Honda Frontier Award" for 2011.
April 14 Prof. Kurihara honored with "A. E. Alexander Lecture Award".
May 9 Prof. Takahashi (PI) was presented in Physics Today.
May 11The paper by Assistant Prof. Sugawara was presented in AIP Advances.
Assistant Prof. Sugawara’s paper

May 11 Prof. Motoko Kotani was assigned as Deputy Director of WPI-AIMR.
June 3WPI Program director, Dr. Kuroki's report on "WPI centers on March 11, 2011 andaftermath"June 13 The paper by Dr. Khademhosseini’s group is listed as the top downloaded paper.
July 8 The paper by Prof. Takahashi's group is selected for one of the most cited articles.
July 19

Prof. Itaya (PI) honored with "The Prix Jacques Tacussel Award of the International
Society of Electrochemistry".

Aug 22

Prof. (PI) Adschiri’s review "Green Materials With Supercritical Water" was selected
for the top ten accessed articles.

Aug 29 Recruitment Program of Global experts by Chinese Government
Sep 12

Research Asso. Kubota’s paper has been selected as Research Highlights in Journal ofApplied Physics

Oct 3

Dr. Khademhosseini, Junior PI, was awarded "Presidential Early Career Award for
Scientists and Engineers (PECASE)*" from the White House.

Oct 17

Dr. Khademhosseini, Junior PI, was awarded “Pioneers of Miniaturization Prize2011” by the Royal Society of Chemistry’s Lab on a Chip Journal.

The paper by Research Associate Xianmin Zhang (Miyazaki Group) has been selected
for the October 31, 2011 issue of Virtual Journal of Nanoscale Science &Nov 7 Vietnam’s Prime Minister Dung visited WPI-AIMR.
Nov 2

AIMR signed MOU on academic exchange with Fraunhofer Institute for Electronic
Nano Systems.
Research result from Takahashi group on a topological insulator was published in
Nov 14 Nature Physics, and the experimental data measured by his group were selected as thecover design.
Nov 18 Prof. Ikuhara (PI) was awarded “Fellow, The American Ceramic Society”.
Nov 10

Nov 21

Dr. Khademhosseini, Junior PI, selected as the 2012 Biotechnology andBioengineering Daniel I.C. Wang Award recipient.

Dec 13 Completion Ceremony of the WPI-AIMR Main Building
The paper by Dr. Hongwen Liu “Single molecule detection from a large-scale SERSDec 13
active Au79Ag21 substrate” was selected as highlight in Nature Asia.
See the followin URL for more details: http://www.wpi-aimr.tohoku.ac.jp/en/modules/newsinfo/

1

Award Information
Awarding
Organization

Date ofAward

The Materials Research Society of JapanJan

The Materials Research Society of JapanJan

A. E. Alexander Lecture

Royal Australian Chemical InstituteJan

Sloan Research fellowship

Alfred P. Sloan Foundation

Feb

Alexander von Humboldt FoundationMar

The Surface Science Society of Japan

February

NEC Tokin CorporationMarch

The Chemical Society of Japan

March

Best Paper Award

The Electrochemical Society of JapanMarch

Device/System

Young Investigator Award

Society for Biomaterials

April

BMG

The 2011 Distinguished AwardThe 8th International Workshop on Intermetallic andAdvanced Materials, China

May

Device/System

Outstanding Paper Award

Transducers

June

Name

Position

ThrustZhongchang Wang*

Assistant Prof.

Materials Physics

Daisuke Ishii*

Assistant Prof.

Device/System

Kazue Kurihara

PISoft Materials

Ali Khademhosseini

Junior PI

Device/System

Yuichi IkuharaPI

Daisuke Ishii*

Assistant Prof.

Device/System

Kazunori Ueno

Assistant Prof.

Materials Physics

Tomokazu Matsue

PI

Device/System

Tomokazu Matsue

PI

Device/System

Ali Khademhosseini

Junior PI

Mingwei ChenPI

Esashi Group

Name of Award
Award for Encouragement of Research ofMaterials ScienceAward for Encouragement of Research ofMaterials Science

Materials Physics Humboldt Research AwardSSSJ Young-Researcher Lecture Award
2010

Tokin Foundation for Advancement of
Science and Technology 22th Research
The Chemical Society of Japan Award
for Creative WorkAli Khademhosseini

Junior PI

Device/System

2011 Y.C. Fung Young Investigator
Award

American Society for Mechanical Engineers (ASME)

June

Alain Reza Yavari

PI

BMG

Award for Scientific Excellence

French National Center for Scientific Research (CNRS)JulyAli Khademhosseini

Junior PI

Device/System

Early Career Award in Nanotechnology

IEEE Advancing Technology for Humanity

August2

Award Information
Name

Position

ThrustShinya Nakano

Research
Assistant

Soft Materials

Ali Khademhosseini

Junior PI

Device/System

Ali Khademhosseini

Junior PI

Device/System

Yuichi IkuharaPI

Ali Khademhosseini

Junior PI

Device/System

Shinya Nakano

Research
Assistant

Soft Materials

Awarding
Organization

Date ofAward
Poster Award of The 63th Divisional Divisional Meeting on Colloid and Interface Chemistry Septembe
Meeting on Colloid and Interface(DMCIC)r
The Royal Society of Chemistry’s "Lab on a Chip
Pioneers of Miniaturization Prize 2011
October
Journal"Presidential Early Career Award for
The White House, the USA
October
Scientists and Engineers (PECASE)

Name of Award

Materials Physics Fellow, the American Ceramics Society

The American Ceramics Society

October

The 2012 Biotechnology andBioengineering Daniel I.C. Wang

Biotechnology & Bioengineering Journal

November

Poster Prize Runner-Up

12th Australia-Japan Colloid & Interface Science
Symposium

November

3

FY2011 List of Major Governmental Research Funds(As of August 1, 2011)
A. Grant-in-Aid for Scientific Research (KAKENHI)(Unit: thousand yen)
BudgetDistribution (*1)

Representative's Name

Categories

Scientific Research on Priority Areas

Scientific Research on Innovative Areas

Scientific Research (S)Scientific Research (A)Scientific Research (B)Scientific Research (C)Challenging Exploratory Research

Young Scientists (A)Young Scientists (B)

TANIGAKI, Katsumi (PI)TANIGAKI, Katsumi (PI)ASAO, Naoki
HITOSUGI, Taro
Subtotal
KURIHARA, Kazue (PI)ASAO, Naoki
HAMADA, Ikutaro
Subtotal
ESASHI, Masayoshi (PI)ADSCHIRI, Tadafumi (PI)
YAMAGUCHI, Masahiko (PI)
TAKAHASHI, Takashi (PI)Subtotal
KOTANI, Motoko (PI)TSUKADA, Masaru (PI)MIYAZAKI, Terunobu (PI)
YAMADA, Kazuyoshi (PI)
MATSUE, Tomokazu (PI)IKUHARA, Yuichi (PI)
YAMAMOTO, Yoshinori (PI)Subtotal
NISHI, Toshio (PI)Subtotal
ASAO, Naoki
TAKEUCHI, Akira
SHIMOMURA, Masatsugu (PI)NAKAJIMA, Ken
SAITO, Mitsuhiro
Subtotal
KOTANI, Motoko (PI)ISHII, Daisuke
NAKAYAMA, Koji
ADSCHIRI, Tadafumi (PI)Subtotal
ISHII, Daisuke
HITOSUGI, Taro
HOJO, Daisuke
Subtotal
LIU, Hongwen
YOSHIDA, Shinya
MCKENNA, Keith Patrick
XU, Limei
JIN, Tienan
FUJINAMI, So
OHSAWA, Takeo
HIRATA, Akihiko
WANG, Zhongchang
LIU, Yanhui
TANABE, Yoichi
JI, Sungdae
TSUKIMOTO, Susumu
Subtotal

Subtotal

4

13

15,10013,3002,100
800
31,30014,6903,510
1,950
20,1504,810
33,28036,40072,410146,900
9,620
9,880
6,240
11,57013,91014,82015,86081,900
650
650
1,170
1,430
910
2,210
2,990
8,710
1,300
2,080
2,730
2,080
8,190
3,510
17,94022,88044,330
650
1,560
1,040
1,170
2,340
650
650
1,300
1,560
1,560
3,510
1,430
2,470
19,89044362,020

4

3

4

7
1

5

4

3

B. Other Grant-in-Aid(Unit: thousand yen)

Representative's NameESASHI, Masayoshi (PI)

BudgetDistribution (*1)

Project Title

Distributing Organization
Japan Society for the Promotion of
Science (JSPS)

Funding Program for WorldLeading Innovative R&D on
Science and Technology

679,000

Subtotal

1

C. Research funds consigned from government directly
Representative's NameADSCHIRI, Tadafumi (PI)TSUKADA, Masaru (PI)KURIHARA, Kazue (PI)
SHIMOMURA, Masatsugu (PI)
KOTANI, Motoko (PI)
YAMADA, Kazuyoshi (PI)ESASHI, Masayoshi (PI)ADSCHIRI, Tadafumi (PI)HITOSUGI, Taro
NAKAYAMA, Koji
FUJITA, Takeshi
IWAYA, Katsuya
SATO, Toyoto

HITOSUGI, Taro

(Unit: thousand yen)
BudgetDistribution (*1)

Project Title

Distributing Organization

Japan Science and Technology Agency Core Research Evolutional Science(JST)
and Technology (CREST)
Japan Science and Technology Agency Core Research Evolutional Science(JST)
and Technology (CREST)
Japan Science and Technology Agency Core Research Evolutional Science(JST)
and Technology (CREST)
Japan Science and Technology Agency Core Research Evolutional Science(JST)
and Technology (CREST)
Japan Science and Technology Agency Core Research Evolutional Science(JST)
and Technology (CREST)
Ministry of Education, Culture, Sports,
Elementary Strategic Project
Science and Technology (MEXT)
Japan Science and Technology Agency Strategic International Cooperative(JST)
Program
Technical Development of Ultrahybrid Materials (Technological
New Energy and Industrial Technology
Development of Contradictory
Development Organization (NEDO)
Functional Materials by nano-scale
Structure Control)
Precusory Research for Embryonic
Japan Science and Technology Agency
Science and Technology(JST)(PRESTO)Japan Science and Technology Agency
Research Seeds Quest Program(JST)
Japan Science and Technology Agency
Research Seeds Quest Program(JST)
Japan Science and Technology Agency
Research Seeds Quest Program(JST)
Japan Science and Technology Agency
Research Seeds Quest Program(JST)
New Energy and Industrial Technology
Development Organization (NEDO)

679,000

7,800
71,76019,50037,713
9,555
4,620

197,157

22,880
5,200
5,850
5,200
2,950

Grant for Industrial Technology
Research (Financial support toyoung researchers)

Subtotal

14,9509,750

14414,885

D. Research funds reconsigned through the private enterprise/university (Unit: thousand yen)
Representative's NameNISHI, Toshio (PI)
SHIMOMURA, Masatsugu (PI)TSUKADA, Masaru (PI)TSUKADA, Masaru (PI)TANIGAKI, Katsumi (PI)HITOSUGI, Taro

BudgetDistribution (*1)

Redistributing Organization

Distributing Organization

New Energy and Industrial Technology
Bridgestone Corporation
Development Organization (NEDO)
New Energy and Industrial Technology Fujifilm Corporation, Japan Tissue
Development Organization (NEDO)
Engineering Co., Ltd. (J-TEC)
Japan Science and Technology Agency Advanced Algorithm and Systems(JST)Co., Ltd.
Ministry of Education, Culture, Sports,
University of Tokyo
Science and Technology (MEXT)
Misitry of Economy, Trade and Industry
Kuramoto Co., Ltd.
(METI)
Japan Society for the Promotion of
University of Tokyo
Science (JSPS)

13,908
9,300
3,120
7,000
2,394
30,193

Subtotal

6

65,915Total

65

1,521,820*1:Budget includes indirect expenses.

5The Fourth Series of WPI-AIMR Joint Seminars FY2011

The topics of the Fourth WPI-AIMR Seminar Series of Fiscal Year 2011 are“Cooperation between Materials Science and Mathematical Science” and composed of
two parts, i.e., (1) ”Mathematical (Math-Mate) lecture + discussions”, and (2)“Materials science presentation + discussion” meetings. The first half of the seminaris assigned to lecture/presentation, and the latter half to questions/ (panel) discussions.
Initial several Seminars should be introductory to form a common understanding among
WPI staffs on the aim/problems of the collaboration with mathematics.
As for the part (2), the speakers are chosen from younger/senior researchers mainly
from WPI-AIMR and they provide topics concerning on the following questions;[1] How does he/she expect the cooperation with mathematics or mathematical science?
[2] What does he/she expect from the concept of “Functon（see below）”
for creating a novel research strategy of materials science?
[3] How can his/her research topics be seen from the view point of Functon?
Proposals of a presentation at the Seminar providing any opinions and related topics
by research members at WPI-AIMR will be most welcome. But Committee membersof Seminars may ask research members to give a talk at one of the Seminars at any
occasion.
Please remind that the participation to this Seminar Series is mandatory.

＊＊＊ about Functon ＊＊＊Definition of the concept of “Functon” itself is the important theme which will be
discussed through this seminar series. Here is a starting point for you to think of it by
yourself.
What is Functon（“機能子” in Japanese and Chinese）?
Functon is a constituent element of materials showing a certain definite function orproperty, and every material is composed of one or many kinds of assembled functons.
The size of functons ranges over from the size of atom/molecule to macroscopic size.
Functons often take spatial or temporal nesting structures, i.e., the structures likematryoshka (Russian doll); higher rank functon is formed as an assembly of lower rankfunctons.

6

Why Functon?
Functon is a central concept introduced at WPI-AIMR to create a novel researchstrategy of materials science. Namely we consider materials science can be performed
without going back to atom/molecule, but by introducing the concept of minimum
function unit, i.e., functons. Working on functons, materials science can be effectively
executed with a help of mathematical science. So far existing materials science
remained the science of matter where properties of matter is solved in turn from thelower to higher rank, i.e., from atom/molecule level to macroscopic level, which
therefore treats ordinary (non-inverse) problems in terms of mathematics. However, atrue materials science should treat an inverse problem to finding out necessary functons
to create novel materials with desired function. Mathematical science should play
important role for that cooperating with materials science.
Functons as a target of mathematical sciences
Mathematical science, of which important tool is the concept of functon helping abridge with the materials science, is needed for solving the difficult inverse problem.
It should solve how to combine complicated multilayer functon systems for the inverse
problem. Furthermore the mathematical science is also expected to help developing
materials as sensitive but robust, and those with multi-functions responding
environment change. Mathematics is also necessary for the control of rare events, andfor device processes utilizing pattern formation and so on. These can be also achieved
with the help of the concept of functons.
Establishing the concept of Functon
Elucidation of easy processes forming higher rank functons from the lower rankfunctons, even from those of atoms/molecules level, and forming functons in artificial
materials, which are related with non-equilibrium open systems, phase transition andnucleation core, interface processes, and self-organization, have been major topics ofindividual materials science so far. However, to create a guiding principle ofinnovative materials science, it is essentially important to explore and establish ageneral concept of “Functon”, and with its bolster, establishing a strategy of a novel
materials design by solving the inverse problem.

7

Report on the 1st Seminar
Nobuaki Aoki
June 24, 2011
“A Role of Mathematics in a New Context– Seek for Possible Collaborations with Materials Science”
Prof. Motoko Kotani“Algorithms for Segment Packing and Generalized Kakeya's Problem”
Prof. Takeshi Tokuyama (GSIS, Tohoku University)
Panel Discussion
The main topic of the 4th WPI-AIMR Joint Seminar Series is “Cooperation between
Materials Science and Mathematical Science”, and having the knowledge on therelationship between mathematics and materials science is the first step for establishing
the cooperation. In the 1st seminar, we had two mathematical lectures and held panel
discussion as a starting point of our scientific exploration.
For the first math lecture, Prof. Kotani presented change in the historical role ofmathematics. She pointed out problems the human society encounter have become
more and more complicated and larger in data-size in the late 1980s, and complexity
beyond the efficiency zone of the existing tools encourages mathematics toacknowledge a new position to handle them. Earlier applications by European Science
Foundation were also introduced and examples of successful collaboration withmaterials science were reported.
In the second lecture, Prof. Tokuyama illustrated a suggestive instance of solving aproblem with the help of accumulation of mathematics over the past hundred years.
The problem was to determine the smallest area from given line segments. It was
solved in the context of computer science, but finding optimal geometric structures
should be an important theme also in material science. He mentioned that such asolving methodology may bridge mathematics and computational material science.
The panel discussion was also held. In order to promote the cooperation withmathematics, we started comprehensive consideration on the materials science as the
combination of element of functions. Following the introductory talk by Dr. Akagi,
several examples of “functional unit (electric circuit, structure of document,
concentration blob in polymer, etc.)” were given by the organizing committee, which
include a suggestive clue to find a non-material functional unit in materials science.

8

Report on the 2nd Seminar
Ryo Nouchi
July 8, 2011““Functon” in Adschiri Group’s Research, Fusion of Ideas in WPI, Analogy & Math”
Prof. Tadafumi Adschiri“What Is Functon, Why Functon and What Can Be Functon”
Prof. Katsumi Tanigaki
Panel Discussion
In this seminar, two Math-Mate talks were given by Prof. Adschiri and Prof. Tanigaki,
which were followed by open discussions entitled “What can be Functon (2)” and“Functon as a Bridge between Materials Science and Mathematics”. In succession to
the 1st seminar, the efforts were made to help materials scientists think of the possible
collaboration with mathematics.
In the first lecture, Prof. Adschiri emphasized needs for high heat conductive
materials to make an efficient recovery system of exhaust heat from automobiles. To
obtain materials possessing this function, Adschiri group has developed super hybridmaterials such as surface-modified nanoparticles, which can be a basic functional
element of this function. He also introduced the research results in WPI-AIMR, which
unveiled similarities between different materials. This kind of analogy between different
materials can be found further in other materials with the help of mathematics.
In the second lecture, Prof. Tanigaki mentioned three inventions that have mostcontributed to science and technology: namely, lasers, transistors, and integrated circuits.
Next, he introduced main research subjects in Tanigaki group, i.e., light-emittingorganic transistors, Dirac-cone states in Fe-based superconductors, and cage-likethermoelectric materials. He also discussed possible basic functional elements forthese three subjects. Finally, he encouraged us to make researches for energy
harvesting without using pseudoscience like Feynman's ratchet.
Following the two Math-Mate talks, we had open discussions, which were led by Dr.
Akagi. At first, Dr. Ikeda made an introductory talk about the role/importance ofmathematics to establish a new scientific principle in materials science. After that, in
succession to the previous seminar, we discussed about re-examination of functional
materials as a combination of basic functional elements in order to make effective
collaborations with mathematics.

9

Report on the 3rd Seminar
Taro Hitosugi and Kazuto Akagi
July 29, 2011
Topological Crystallography－ Commemorating the fourth centennial anniversary of the publication of Kepler's
pamphlet “New-Year's gift concerning six-cornered snow” (1611) –Prof. Toshikazu Sunada (Meiji University)
One-dimensional exotic-nanocarbon: Electrons in a Riemannian space
Prof. Jun Onoe (Tokyo Institute of Technology)
In this seminar, two talks were given by Profs. Sunada and Onoe, both encouraging
our efforts to help materials scientists think of the possible collaboration withmathematics.
In the first lecture, mathematician Prof. Sunada gave a brief history of crystallography,
a practical science that originated in the classification of the observed shapes of crystals,
to provide the audience with a mathematical insight into modern crystallography. Thenthe talk went in to the formulation of a minimum principle for crystals in the frameworkof discrete geometric analysis, and predicted a new crystal based on K4 structure.
He expects the synthesis of the predicted material, and emphasized that topologicalcrystallography vigorously interacts with other fields in pure mathematics and also withmaterials science.
The next speaker, a materials scientist Prof. Onoe, talked about their observation of
Riemannian geometrical effects on the electronic properties of materials such as
Tomononaga-Luttinger liquids, which were previously theoretically predicted by theirgroup. They have examined a one-dimensional metallic C 60 polymer with an uneven
periodic peanut-shaped structure using in situ high-resolution ultraviolet photoemission
spectroscopy.
Their successful combination of materials science and mathematics was quite
impressive, and suggests one of the ways of research in WPI-AIMR.

10

Report on the 4th Seminar
Kazuto Akagi
August 26, 2011
“A map of mathematics for materials scientists”
Kazuto Akagi“Why mathematics?”
Prof. Masatsugu Shimomura
In the past three seminars, we had several Math-Mate talks and open discussions onwhat we are aiming for through the fusion with mathematics. This attempt looks
basically going well so far, but it is also true that we cannot well imagine “what really
becomes possible by collaboration with mathematicians”, still now. Therefore, two talks
introducing how to interact with mathematics were given at this timing.
In the former part of the talk by Akagi, the world of mathematics was overviewed
with simplified explanations on each field. Next, an example was introduced how chaostheory helped to analyze and stabilize the behavior of a furnace based on very limited
numbers of monitoring data and a simplified physical model. Materials scientists are
more or less familiar with the basic scientific framework (e.g. classical mechanics,
thermodynamics, electromagnetics, statistical mechanics, quantum mechanics) and use
it in their thinking. In the same way, we need to know minimum level of knowledge
about the framework of mathematics (= a map of mathematical world) though we neednot do mathematics itself, he said.
In the second talk, Prof. Shimomura gave a talk on “why mathematics” based on his
experiences of collaboration with mathematicians in the field of biomimetics. One of
the impressive examples was the biomimetics database aiming for contribution to otherwide scientific and engineering fields including materials science. It is based on thedigital image processing technology developed by Prof. Haseyama (Hokkaido Univ.),
which helps us recognize buried similarity or relevance in enormous data one after
another. As Prof. Nishiura says, mathematics is a ubiquitous tool.

11

Report on the 5th Seminar
Kazuto Akagi
October 6, 2011
“Protein Structure and Topology”
Prof. Hiroaki Hiraoka (Kyushu University)
In this seminar, applications of computational homology to analysis of proteins wereshown. In particular, compressibility of proteins was chosen as an example of structuralproperties, and it was successfully correlated with some topological properties such as
robust "hole" in the protein modeled by van der Waals balls.
The lecturer used Homology groups as algebraic tools to study such geometrical"holes". In this framework, “simplicial complex” is given as an input data, and various
geometrical properties such as connectivity (H 0 ), loop (H 1 ), cavity (H 2 ), n-dimensionalhole (H n) are obtained as outputs. Here, “simplicial complex” is a connection oftetrahedrons whose faces are shared by each other. They say pixel processing incomputer graphics is similar to this transform to “simplicial complex”.
He says that recent progress on computational homology allows us to easily treat
them by using computers, and emphasizes that this approach is widely applicable tovarious targets, not only realistic objects but also abstracted ones including
n-dimensional data structures. Some people seemed to be inspired to use it for analysisof the relation between structure and property in BMG systems. My approach toaqueous solution systems focusing on the structure of hydrogen-bond network can besophisticated using this method. Indeed, abstraction of the topological structure fromour research objects in materials science should be one of the helpful approaches toclarify the nature in them.

12

Report on the 6th Seminar
Susumu Tsukimoto
October 27, 2011
“Cantor sets meet the brain”
Prof. Ichiro Tsuda (Hokkaido University)
In this seminar, the talk were given by Prof. Tsuda who is an authority on chaos incomplex systems and is recently studying on chaotic dynamics of the brain, entitled“Cantor sets meet the brain” and were followed by open discussions in order to have aclue for bridging between materials science and mathematics in WPI-AIMR.
Prof. Tsuda first introduced Libchaber’s thesis which clearly described how amathematical theorem takes part in an actual proof in laboratories. Then, he talked
about the research example of this thesis, which is on a “mathematical model” forarchicortex proposed to explain the formation of episodic memories in the brain base on
the network structure of the hippocampus which provides fields for the creation ofinternal time connecting the past, present, and future. The theoretical model showingthat the hippocampus plays a role in formation of dynamic memory via multiple
time-scales interactions was presented in this seminar. He talked about the study with asimilarity between the structures of hippocampal CA3 and CA1 and of two variables
constructing a skinny baker’s map, which is a typical two-dimensional chaotic map. The
structure gave a hint to make a mathematical model of the hippocampus which is
responsible for the formation of episodic memory. By correlating between experimental
and mathematical studies of the network structures, chaotic behaviors were observed in
hippocampal CA3, and also a Cantor set in hippocampal CA1. This example could
suggest a promising relationship between mathematical and experiment studies ofdynamic behavior in the brain science.
Following his talk, we organized open discussions, which were led by Dr. Tsukimoto.
At first, Prof. Tanigaki asked a question on the experimental measurements of signals inneuron. In order to make effective collaborations between mathematics and materials
science, Dr. Nakajima asked the speaker about possibility of Cantor set and/or othermathematical models to apply to materials science field as well as brain science.

13

Report on the 7th Seminar
Ken Nakajima
November 25, 2011
“Simulation study of a local glass transition temperature in polymer thin film”
Dr. Hiroshi Morita (AIST)In this seminar, Dr. Morita introduced their study on a local glass transition and apolymer chain dynamics in polymeric materials using coarse-grained molecular
dynamics (MD) simulation. According to his talk, the dynamics of the polymer chain in
the confined geometry is different from that of the bulk, and these situations can beobserved in many materials. Recently, Prof. Tanaka and co-workers in Kyushu
University measured the glass transition temperature (T g ) near the substrate and it
became larger as the analytical depth from the substrate became smaller and smaller.
Furthermore, T g of filler-contained polymeric materials were also measured by themand the feature of T g was considered as a relation to T g near the substrate. To clarify
these problems, Dr. Morita conducted the coarse-grained MD simulation. He also
briefly explained the coarse-graining technique and the simulation system of OCTA,
which was developed by Prof. Masao Doi’s group in The University of Tokyo,
including Dr. Morita himself (http://octa.jp/).
After his talk, there were extensive questions and discussions. One arose from a
researcher from the polymer group was the effect of the change in T g to mechanicalproperties. This is actually important and we reached the conclusion that we need afurther collaboration with Dr. Morita. A researcher in the BMG group put a question
about the T g change at surfaces. This is because it would be very interesting if this effectis also seen in BMG materials. Dr. Morita pointed out the possible parameters for thisphenomenon. We will be able to study this point in the near future. Another question
was the inhomogeneity recently observed in BMG and polymer surfaces by researchers
in WPI-AIMR. He seemed to be interested in it. He will check his data in more detail interms of inhomogeneity and will give us a report on it soon.
This time, he tried to talk the glass-transition phenomena as a generalized problem
seen in many different types of materials and the audience agreed his point.

14

Nanomaterial Transport by Motor Proteins
Daniel Oliveira1 and Winfried Teizer1,2
1

WPI Advanced Institute for Materials Research, Tohoku University

2

Department of Physics and Astronomy, Texas A&M University, College
Station, TX, United States.

1. Introduction
Protein machines, also referred to as molecular motors, are the origin of nearly all
biological movements within the eukaryotic cell. Conversion of chemical energy intomechanical work, harnessed by the hydrolysis of ATP, propels proteins’ alongcytoplasmic systems of fibers,
such as microtubules.
The
kinesin protein (Figure 1) is awell known naturally occurring
molecular machine capable ofunidirectional cargo transport
Figure 1. Kinesin dimer structure showing the heavyupon microtubule interaction,
chain (head domain) and the light-chain (tail domain).
and consequently an attractive
candidate as a constituent of a synthetic molecular machine. As illustrated in Figure 2,
within the cytoskeletal network kinesin moves toward the (+)-terminus of microtubules(anterograde transport) having several functions including synapse activity [1,2].
Recent efforts to engineer tailor-made artificial nanotransport systems in order tocarry out directional transport of nanoobjects in a cell-free environment are thus hardly
surprising [3,4]. In a typical design, ATP-fueled kinesin motor proteins areimmobilized on a glass surface while microtubules loaded with cargo are propelled overthe motors. Alternatively, molecular shuttles can be assembled mimicking the naturalcell`s intracellular transport mechanism where the kinesin protein moves overmicrotubules tracks (Figure 2). From a device engineering perspective, the latterapproach for molecular shuttles is more appealing since multiple microtubules tracks
with varying directions can be designed in the same device; moreover, bidirectionalcargo transport can be achieved on the same track if different motor proteins are used
(e.g., kinesin and dynein). Therefore, it is conceivable to utilize this concept fornanoelectromechanical systems. Kinesin motors have, in fact, been successfully used15

for applications such as biomedical sensors [5], bio-molecular motion [6], andnanoparticle transport [7].
Relying on very strong and specific covalent
Microtubule
Kinesininteractions (e.g., biotin-avidin) kinesin can becoupled to functionalized nanocrystals, andaccordingly, the interaction of such a complex with Fluorescent Cargo
microtubules tracks can be visualized and investigated.
It is therefore anticipated that molecular shuttles canbe engineered by manipulating not only the cargo to
be transported by kinesin but also the microtubule
track network. This work is expected to develop
Figure 2. Kinesin-Microtubule
novel opportunities for nanosize transport, especiallyInteraction for Cargo Transport.
for drug delivery.

2. Kinesin expression and kinesin-microtubule interaction observation
The first step toward the implementation of functional kinesin molecular shuttles isthe construction, expression and purification of biotinylated kinesin dimers [8,9],
currently performed in collaboration with Prof. Mitsuo Umetsu (WPI-AIMR at Tohoku
University). Typically, the drosophila DNA fragment encoding the full-length kinesin
heavy-chain motor domain is designed and modified by incorporating sequences ofhexa-histidine and biotin tags. The recombinant kinesin protein is then expressed in
Escherichia coli cells and purified by Ni-NTA chromatography. Following protein
purification, the biotinylated recombinant kinesin protein is conjugated withstreptavidin (or avidin) coated nanoparticles. Commercially available streptavidincoated quantum dots (Invitrogen Corp.) are currently used for preliminary experiments
on kinesin motility on microtubules. Microtubules (rhodamine-labeled) and fluorescent
nanoparticles are then observed on an Olympus BX-51 fluorescence microscope, incollaboration with Prof. Tadafumi Adschiri (WPI-AIMR at Tohoku University).
3. Results and discussion
Two methods were used to quantify the relative amount of kinesin protein expressedin Escherichia coli, namely, sodium dodecyl sulfate polyacrylamide gel electrophoresis(SDS-PAGE), and Western Blot analysis of electrophoretic separated kinesin. Bothmethods rely on the electrophoretic separation of proteins based on their sizes, differingin how the sought protein is visualized. The later method estimates the molecular mass16

of a protein by comparison with a protein standard, whereas in the former, protein
visualization is achieved using fluorescent-labeled antibodies specific to the target
protein (here, a his-tag antibody). Figure 3-A shows the SDS-PAGE result for the
expressed kinesin heavy chain in Escherichia coli purified in a Ni Sepharose column
and separated by size exclusion chromatography using a Superdex 200 column.
Following electrophoresis, the polyacrylamide gel was stained with coomassie brilliant
blue dye to allow visualization of separated protein bands, as seen in the figure. The
first lane in the SDS-PAGE corresponds to the molecular weight marker (New England
Biolabs), whereas lanes 2-10 are different Superdex 200 elution fractions. Since thedesigned kinesin protein has a molecular weight of 48 kDa, observation of Figure 3-A
seems to indicate the presence of kinesin in fractions 2-10. Kinesin expression was
supported by the Western Blot technique, where eluted fractions shown in Figure 3-A
where detected with a fluorescent-labeled his-tag antibody (Santa Cruz Biotechnology).
As illustrated in Figure 3-B, the kinesin protein was confirmed to be present in fractions
2-10.
k Da
175

1

2

3

4

5

6

7

8

9

10

A

1

2

3

4

5

6

7

8

9 10

B

80
58
46

30

Figure 3. (A) SDS-PAGE: Lane 1, Molecular Marker; Lanes 2-10, Superdex 200 eluted
fractions. (B) Western Blot with fluorescent labeled his-tag antibody: Lane 1, MolecularMarker; Lanes 2-10, Superdex 200 eluted fractions.

Following successful kinesin heavy chain preparation, the formation of microtubules
was studied by controlling the polymerization of tubulin. A mixture of unlabelledtubulin and rhodamine-labelled tubulin was polymerized yielding stable fluorescent
microtubules. Flow-cells constructed by the juxtaposition of KOH-cleaned cover slip
and a microscope slide using double sided tape were used to observe microtubules withthe fluorescent microscope. GTP (Guanosine-5'-Triphosphate) analogs are known topromote the polymerization of microtubules and also to prevent their depolymerization[10]; therefore, two GTP analogs where tested to study the difference, if any, in
prepared fluorescent labeled microtubules, namely guanosine-5-[(,)-methyleno]17triphosphate, and guanosine-5'-monophosphate salts. It turns out that microtubules
prepared with the latter salt are considerably longer than the ones prepared with theformer salt. The reason for this is currently under investigation. Since the major
components of the constructed nanotransport system are fluorescent (rhodaminelabelled microtubules for tracks and fluorescent quantum dots to be transported bykinesin), fluorescence microscopy is an elegant choice to visualize such systems.
Microtubules shown in Figures 4-A and B were obtained after guanosine-5'monophosphate salts polymerization, and microtubules on Figures 4-C and D werevisualized after guanosine-5-[(,)-methyleno] triphosphate polymerization. A clear size
difference in microtubules polymerized with the two distinct promoters can be easily
observed by the corresponding fluorescence images.
A

C

B

D

Figure 4. Microtubule fluorescent images. (A) and (B)microtubules

polymerized in the presence of Guanosine-5'-monophosphate salts; (C) and (D)microtubules polymerized with Guanosine-5-[(,)-methyleno] triphosphate.
Scale bar is 20 µm.

Following microtubule fluorescence observation, the kinesin-semiconductor
nanocrystals complex, which consisted of biotinylated kinesin labeled withcommercially available streptavidin-coated quantum dots (Qdot 605 nm, InvitrogenCorp), was assembled using a mixing ratio of 7 kinesin monomers per quantum dot. To
visualize the kinesin-quantum dot conjugate interacting with the microtubule track, the18

same procedure described in Figure 4 was followedA
except that after injecting the microtubule solution, thekinesin/quantum dot complex was flushed into the flow
cell. Because of the linear motion observed, Figures 5
A-C are interpreted to show quantum dot motion along
20 µm
microtubules, where pictures A to C correspond tofluorescent time elapsed images collected every 500 ms,
Brespectively. Due to equipment limitation, we are notable at the present time to unambiguously rule out otherinterpretations since no microtubules were directly
20 µm
observed near the quantum dots. Efforts are currently
being made to overcome the problems in the fluorescentobservation of kinesin-quantum dot conjugates by (1)Cusing semiconductor nanocrystals with different
emission wavelengths, (2) altering the length of
microtubules, and (3) varying the ratio of kinesin to
20 µm
quantum dots. It should be noted that the fluorescence
images shown in Figures 4 and 5 were obtained with a
Figure 5. QD motion along
relatively low resolution system, coupled with a standard
microtubules. Images (A),CCD camera (DP71).
We are in fact currently(B) and (C) were collectedassembling a state-of-the-art microscope at WPI-AIMR
with 500 ms intervals.
capable of providing the high level of precision andaccuracy required for the direct observation of microtubules and more importantly,
kinesin/nanoparticle complex motion on microtubules networks. Such a system, whichis expected to be fully operational in September 2010, consists of an inverted
fluorescence microscope (IX71, Olympus) equipped with a Total Internal Reflection
condenser (IX2-RFAEVA, Olympus); evanescent illumination will be provided by the
488 nm line of an argon ion laser. Fluorescent images will be acquired with an electron
multiplier charge couple device (ImageEM C9100-13, Hamamatsu). With this new
instrument, we expect to be able to resolve and distinguish microtubules and quantum
dots simultaneously.
3. Summary
We have initiated an effort at WPI-AIMR in early 2010, which is aimed atunderstanding and constructing novel biomolecular systems for nanomaterials transport.
Recombinant kinesin heavy chains have been expressed in Escherichia coli cells and19confirmed based on their molecular weight by SDS-PAGE and Western blot. In
addition, microtubules networks were systematically polymerized and their length could
be manipulated by controlling the addition of specific polymerizing promoter reagents.
Furthermore, the artificially created kinesin proteins could be conjugated withfluorescent-labeled quantum dots and visualized by fluorescence microscopy. Deeper
insight into such nanoscale transport systems will be achieved once the Total Internal
Reflection Fluorescence (TIRF) microscope is fully operational, providing the highlevel of precision and accuracy required to the direct observation of such phenomena.
Acknowledgements
We acknowledge crucial support by our collaborators in the laboratories of Prof.
Adschiri and Prof. Umetsu.
References[1] A. Goel and V. Vogel Nat. Nanotech. 3, 465-475 (2008).
[2] R. Dixit, J. L. Ross, Y. E. Goldman and E. L. F. Holzbaur Science 319, 1086-1089(2008).
[3] J. Noel, W. Teizer and W. Hwang ACS Nano 3, 1938-1946 (2009).
[4] J. Noel, W. Teizer and W. Hwang Journal of Visualized Experiments 30, (2009).
http://www.jove.com/index/details.stp?id=1390[5] T. Fischer, A. Agarwal and H. Hess Nat. Nanotechnol. 4, 162-166 (2009).
[6] M. G. L. van den Heuvel and C. Dekker Science 317, 333-336 (2007).
[7] R. K. Doot, H. Hess and V. Vogel Soft Matter 3, 349-356 (2007).
[8] G. D. Bachand, S. B. Rivera, A. K. Boal, J. Gaudioso, J. Liu and B. C. Bunker Nano
Lett. 4, 817-821 (2004).
[9] D. L. Coy, M. Wagenbach and J. Howard J. Biol. Chem. 274, 3667-3671 (1999).
[10] T. Mitchison and M. Kirschner Nature 312, 237-242 (1984).

20

Engineering the Cellular Microenvironment
Hongkai Wu
WPI Advanced Institute for Materials Research, Tohoku University
Hong Kong University of Science and Technology, Hong Kong, P. R. China

Human physiology associates specific functions with each organ, for example,
the liver acts as a filter for harmful substances contained within blood, it stores vitamins
and minerals, and it produces cholesterol whereas the kidney filters blood and makes
urine. These functions are specific to tissues even though the cells that make up
tissues exhibit plasticity in their differentiated state. The earliest examples that exploit
the instability of cells in tissues induced corneal epithelium to produce hair andtransformed carcinoma cells into normal tissues (Figure 1) [1, 2]. These examples

Figure 1. The role of the cellular environment.

The embryonic recombination of mouse

ectoderm with chick mesoderm produces an identity determined by the ectoderm; in this case,l

ith lif thdindicated that the cellular microenvironment played an essential role in the function ofcells.
Materials and Methods for Engineering the Cellular Microenvironment.
Researchers can create tissue-like microenvironments using tissue extracts orsynthetic hydrogels. These materials include alginate, collagen [3], laminin-rich ECM[4], Matrigel (extracted from Engelbreth-Holm-Swarm mouse sarcoma), andphotosensitive hydrogels [5]. The purpose of synthesizing and using biocompatible
materials and fabricating ordered structures from these materials is to control thelocation of cells within the structured material. A suite of rapid prototyping tools
developed under the heading of ‘soft lithography’ makes the patterning and control ofliquids and polymers at the microscale possible [6]. Combining soft lithography with
the natural and synthetic materials for cell culture presents intriguing possibilities for21

controlling where cells grow in 3D, stimulating selective populations of cells, andengineering tissues from several types of cells.
Takeuchi et al. used an axisymmetric flow-focusing microfluidic device tofabricate hydrogel beads that contained cells [7]; the hydrogel beads self-assembled
from a solution of peptides when exposed to ions. The combination of microfluidics,
materials science, and cell biology exemplified in this work solved several problems forcell culture in 3D, namely, eliminating large chemical gradients that characterize
millimeter-sized gels formed using conventional well plates and it simplified the
preparation of beads that contain multiple types of cells. The same combination of
microtechnology and biomaterials can provide control over the assembly of individual
pieces of engineered tissue constructs. Sia et al. demonstrated the use of hydrogels
that contain fibers of collagen that attach to neighboring hydrogels that contain fibers ofcollagen [8]. The ability to control how different and multiple phases of hydrogels
interact at the molecular scale is likely to instruct the assembly of complex tissues using
natural materials.
Several methods are available that produce aggregates of cells without using any
material substitute for the ECM; these methods include suspending a drop of cells on an
inverted substrate [9] and confining cells to chemically and topographically defined
regions of a substrate (Figure 2) [10–12]. The design of micron sized tissues using
Figure 2.

Substrates that contain topography cause cells to aggregate into spheroids.

Apattern of adhesive (collagen) and non-adhesive (poly(ethylene glycol), PEG) regions arefabricated in a microwell using a stamp.

Cells adhere selectively to the collagen and theaggregates enables the size of the tissue to be controlled, which maximizes aggregate
size and prevents oxygen and nutrient deficiencies within the aggregate; multiple typesof cells can assemble in aggregates and organize among themselves; and, unlike
microfluidics, the forces that cells experience during aggregation are unlikely to affecttheir function.

Biological Phenomena Unique to Cell Culture in 3D.
What is probably most compelling in justifying the study of 3D cell culture is
the manifest differences in behavior between cells cultured on two-dimensional
substrata and those in three-dimensional matrices. The morphological differences
between cells cultured in 2D and 3D are distinct. In 3D, fibroblast cells exhibit

22

dendritic extensions or are bipolar and stellate (which morphology is observed is afunction of how restrained and stiff the matrix is), however, on 2D substrata fibroblast
cells are flat and are distinguished by stress fibers.
Bissell et al. developed a conceptual framework for thinking about therelationship between cells and their microenvironment using breast cancer as a model
system [13, 14]. One of several outcomes from this framework was evidence that 3D
cell culture models can be used to identify functional genes and proteins and validate
targets for therapy. For example, the ß1-integrin receptor mediates cell-extracellularmatrix interactions and increased expression of ß1-integrin correlated with poor survival
in patients, however, down-modulation of ß1-integrin results in reversion of themalignant phenotype by arresting growth and restoring tissue polarity when propagatedin a 3D microenvironment. Addition of ß1-integrin inhibitory antibody to tumor cells
cultured in laminin-rich ECM gels decreased the rate of proliferation and numbers ofcells and increased apoptosis.
The relationship between, for example, fibroblasts and collagen matrix isreciprocal: fibroblast cells remodel the matrix, which increases the tension within thematrix, which feeds back into the cells and alters the mechanisms that are used tofurther remodel the matrix. Primary hepatocytes, when cultured on collagen orbasement membrane proteins, assume their differentiated shape and they express highlevels of mRNA for liver-specific genes [15]; in contrast, the same cells cultured onplastic substrata exhibit a dedifferentiated, flattened shape, because the substratum isinelastic; liver-specific gene transcription also declines dramatically on flat substrata.
Aggregates of cells can be used to produce protein therapeutics in quantities
several times greater than the amounts produced by suspended cells in protein-free
media, however, it is unclear if this phenomenon can scale to compete withbioprocesses that are currently used for production of proteins [9].
Our Research Program.
Our lab focuses on problems that exist at the interface of microfabrication,materials science, microscopy, and cell biology and range from manipulating individual
cells to organizing thousands of cells.
We demonstrated the fabrication ofmonodispersed alginate gels that contained cells using biocompatible polymer
membranes (Figure 3) [16] and we developed methods that modify the most popularmaterial for microfluidics research (poly(dimethylsiloxane), PDMS) with fluorescent23

quantum dots for sensitive readout of temperature in microchannels [17] and withparaffin wax, which rendered PDMS airtight [18].

Our recent work uses topographically defined substrates to create spheroid
cultures of cells and organizes multiple types of cells cultured in collagen gels. These
projects are part of our continuing efforts to demonstrate the simplest methods that canculture cells in their natural environments and to characterize their behavior using
accessible microscopy tools. We expect the outcome of our efforts to define methods
that provide appropriate metabolites and nutrients for each type of cell in a multicellular
engineered tissue.
References.
[1] JL Coulombre and Coulombre A.J. Dev. Biol. 25, 464 (1971).
[2] C. Ferraris, C. Chaloin-Dufau, and Dhouailly D. Differentiation 57, 89 (1994).
[3] R.B. Vernon and Gooden M.D. In Vitro Cell. Dev. Biol. 38, 97 (2002).
[4] N. Boudreau, C. Myers, Bissell M.J. Trends Cell Biol. 5, 1 (1995).
[5] Hubbell J.A. Curr. Opin. Biotech. 14, 551 (2003) and references therein.
[6] Y. Xia and Whitesides G.M. Angew. Chem., Int. Ed. 37, 550 (1998).
[7] Y. Tsuda, Y. Morimoto and Takeuchi S. Langmuir. 26, 2645 (2009).
[8] B.M. Gillette, J.A. Jensen, B. Tang, G.J. Yang, A. Bazargan-Lari, M. Zhong and Sia
S.K. Nat. Materials. 7, 636 (2008).
[9] J.M. Kelm and Fussenegger M. Trends Biotech. 22, 195 (2004).
[10] J. Fukuda, Y. Sakai and Nakazawa K. Biomat. 27, 1061 (2006).
[11] D.M. Dean, A.P. Napolitano, J. Youssef and Morgan J.R. FASEB J. 21, 4005
(2007).
[12] A.P. Napolitano, P. Chai, D.M. Dean and Morgan J.R. Tissue Eng. 13, 2087 (2007).
Figure 3. Fabrication of individual pieces of hydrogel that contain bacterial cells using a
microfabricated membrane.

PDMS wells pattern the location and geometry of a solution ofalginate, which is converted to a gel when exposed to a solution of divalent ions, for example,[13] H. Liu, D.C. Radisky, F. Wang and Bissell M.J. J. Cell Biol. 164, 603 (2004).
[14] C.C. Park, H. Zhang, M. Pallavicini, J.W. Gray, F. Baehner, C.J. Park et al. Cancer
Res. 66, 1526 (2006).
[15] C.M. DiPersio, D. Jackson and Zaret K.S. Mol. Cell. Biol. 11, 4405 (1991).

24

[16] C. Qiu, M. Chen, H. Yan and Wu H.K. Adv. Mater. 19, 1603 (2007).
[17] J.H. Zhou, H. Yan, Y.Z. Zheng and Wu H.K. Adv. Func. Mater. 19, 324 (2009).
[18] K.N. Ren, Y.H. Zhao, J. Su, D. Ryan and Wu H.K. Anal. Chem. 82, 5965 (2010).

25

Development of Novel Methods of Surface Forces Measurement
for Nano-Materials Science
Kazue Kurihara
WPI Advanced Institute for Materials Research & IMRAM, Tohoku University,
Katahira, Aoba-ku, Sendai 980-8577, Japan
E-mail: kurihara@tagen.tohoku.ac.jp
1. Introduction
One of important challenges in advanced materials science is bridging a gap between
materials nano-science and real materials, that is, designing real materials in nano-scaleprecision like biological systems. In order to achieve this goal, it is essential toelucidate and regulate molecular and surface interactions. Self-assembly is essential at
all scales in biology, which demonstrates an ideal model for designing materials at theatomic and/or molecular level of precision.
Surface forces measurement and atomic force microscopy (AFM) have made it
possible to directly measure molecular and surface interactions in liquids as a functionof the surface separation with high sensitivity. Naturally, they have become powerfultools for studying the origins of forces operating between molecules and/or surfaces ofinterest [1, 2]. They also offer a unique, novel surface characterization method, which“monitors surface properties changing from the surface to the bulk (depth profiles)” andprovides new insights into surface phenomena [3]. This method is direct and simple. It
is difficult to obtain a similar depth profile by other methods; X-ray and neutron
scattering measurements can provide similar information but require extensive
instrumentation and appropriate analytical models.
Our research concerns “ elucidation of molecular and surface interactions as well as
surface properties of nano-materials” , and “ development of novel functionalized
molecular architectures” . For this purpose, we use the surface forces measurement asa major tool. Molecular architectures are self-organized polymolecular systems wheremolecular interactions play important roles. They exhibit specific and unique functions
that could not be afforded by single molecules. Molecular architecture chemistrybeyond molecules is not only gaining a central position in chemistry but becoming animportant interdisciplinary field of science [4]. Recently, the concept has extended toarchitectures of nano-scopic objects such as nano-particles and nano-rods [5].
Investigation of molecular architectures by surface forces measurement is importantfrom the following points of view.

126

(1) It is essential to elucidate intermolecular and surface interactions involved in selforganization, of which significance is not limited to material science but extends tothe ingenuity of biological systems.
(2) The importance of surface characterization in molecular architecture chemistry andengineering is obvious since solid surfaces are becoming essential building blocks
for constructing molecular architectures as demonstrated in self-assembled
monolayer formation and alternate layer-by-layer adsorption [6], and assembles ofnano-particls [5]. Surface-induced structuring of liquids is also well-known [7, 8],
which bears implications for micro- and nano-technologies (i.e., liquid crystal
displays and micromachines). Because surface forces are sensitive to change insurface force characteristics, force measurement could point out intriguing
phenomena. For example, we found novel molecular architecture (alcohol
macroclusters) at solid –liquid interfaces [9, 10].
(3) Two-dimensionally organized molecular architectures can be used to simplify thecomplexities of three-dimensional solutions and allow the surface forces
measurement. By employing this approach, we can study complex systems such as
polypeptides and polyelectrolytes in solutions [11], and specific interactions ofproteins [12].
Earlier studies of surface forces measurement were mainly concerned with surface
interactions determining the colloidal stability including surfactant assemblies [1, 2]. It
has been demonstrated, however, that a “force-distance” curve can provide much richer
information on surface molecules; thus it should be utilized for studying a wider rangeof phenomena [13]. Practically, the preparations of well-defined surfaces, mostly
modified by two-dimensional organized molecules, and the characterization of thesurfaces by complementary techniques are keys to this approach. A similar concept is“force spectroscopy” [14], coined to address force as a new parameter for monitoring
the properties of materials. A major interest in force spectroscopy is the single
molecular measurement generally employing an atomic force microscope [15]. On theother hand, the forces measurement of two-dimensionally organized molecules has
advantages complementary to those of single molecule force spectroscopy. It canmonitor many molecules at the same time and thus is better suited for studying longrange weaker forces. The measurement should bear a close relevance to real systems
that consist of many molecules, because interactions between multiple molecules and/or
macroscopic surfaces in solvents may exhibit characteristics different from thosebetween single molecules. The surface forces measurement possesses its own virtue.
In spite of its obvious importance, the surface forces measurement remained a27
2

relatively specific tool in the field of colloid
and interface science. A major drawback ofsurface forces measurement employing
surface forces apparatus (SFA) is restrictionof samples: it is applicable only fortransparent substrates and liquids because it
uses FECO fringes for the distancedetermination [1].
We have recently
developed a novel SFA, a twin-path SFA(Figure 1), which is a practically only SFA
Figure 1. Photograph of a major
for opaque samples [16].
part of the twin-path SFA.
Another instrumentation we have
involved is the shear force measurements. Taking an advantage from an ability of thesurface forces apparatus to regulate the surface separation with a high resolution,
various shear measurements have been developed to study confined liquids. This paper
describes the resonance shear measurements (RSM) which we have also recently
developed [17]. Using this measurement, it is possible to perform measurement fornano-rheology and nano-tribology.
2. Experimental Section
2.1 Twin-path Surface Forces Apparatus(Twin-path SFA)
A schematic diagram of the twin-path
SFA is shown in Figure 2. The top
surface is fixed to the stainless steel
chamber and the bottom surface ismounted on a double-cantilever spring
supported by a shaft connected to thesurface drive system.
The distance
between surfaces was mechanicallycontrolled by the drive system composedof a pulse motor (Oriental Motor Co.,
Ltd.) in combination with the differential
spring. The displacement of the bottom
surface was measured using the twin-path
distance measurement unit.

Figure 2. Schematic diagram of the twin
path SFA. Laser light (λ = 670 nm) goes
through the window at the bottom ofchamber and is reflected by the back of
the disk holder. The reflected light ismonitored by the twin path unit. The
surface distance is controlled by asurface drive system.

28
3

The mica surfaces glued on silica
lenses were mounted in the SFA chamber,and the distance between them wasmeasured by FECO (Fronges of Equal
Chromatic Order) using the common
procedure [1]. The lower surface wasdriven by a certain number of counts and Figure 3. Schematic figures of thethe change in the distance was twin path distance measurement unit
determined.
The displacement/pulse ((a) front view and (b) side view).
The +1st and –1st order beams arethus determined was 0.0050 ± 0.0002 nm
reflected by the bottom of the disk
in the working range of 4 μm.
holder and that by the fixed mirrors,
The detail description of the twin path respectively and are recombined on
Theunit is shown in Figure 3. The collimated the diffraction grating.
recombined beam is detected by thelight beam emitted from a laser diode (λ 4-sectored photo diode and analyzed= 670 nm) (Applied Techno Corp.), was by the PC.
split into several orders ofinterferometric
light
by
a
diffraction grating. The +1st orderdiffracted light was entered to the
SFA chamber from the bottom
window and reflected by the mirrorof the lower sample holder, while
the –1st order diffracted light isreflected by the fixed mirrors in the Figure 4. Schematic figure of the changes
twin path unit. These reflected in the intensities of laser light (CH1, solid
lights are recombined with each circles; CH2, open circles; CH3, solid
triangles; CH4, open triangles) and obtained
other on the four diffraction
phase differences shown as jagged curves
gratings attached to the four- ( φ , solid line; φ , broken line) on
1
2
sectored photo diode (Hamamatsu approach.
Photonics K. K.). The different
intensities of the interference pattern with the phase shift of 0, 90, 180, 270 degrees
were detected by the four-sectored photo diode (Figure 4). The phase difference
between the ± 1st order lights is calculated using the following équation[18],φ1 = arctan{(I 4 − I 2 )/ (I 1 − I 3 )}

4
29

(1)

where φ1 is the phase difference (degree) and I 1 , I 2 , I 3 , and I 4 are the intensities of thelight recorded by Channel 1 (CH1), 2 (CH2), 3 (CH3), and 4 (CH4) of the four-sectored
photo diode, respectively. This phase difference shows the jagged curve with thechange in the surface displacement as shown in Figure 3. The surface displacement, D(nm), can be obtained from the équation [18],
D=

1 φ1
×λ
2 360

(2)

where λ is the wavelength of laser light ( λ = 670 nm).
The resolution of the surface displacement would be low at the steep gradient parts of
φ1 as shown in Figure 3. To avoid this problem, we calculate simultaneously the phasedifference, φ 2 , by equation (3),φ 2 = arctan{(I 3 − I 1 )/ (I 4 − I 2 )}(3)

to replace φ1 in equation (2), when the φ1 is in steep gradient parts.
2.2 Resonance Shear Measurement (RSM)
A photograph and a schematic drawingof the device for resonance shear
measurement are shown in Figure 5. The
droplet of a liquid was confined between
upper and lower solid (typically mica orsilica) surfaces. The upper surface waslaterally oscillated with various frequencies
by applying the sinusoidal voltage (U in and–U in ) to the two opposite electrodes of the
four-sectored piezo tube. The movement of
the upper surface is monitored by thecapacitance probe, and the output voltage(U out ) was plotted as the amplitude ratio of
U out /U in as a function of frequency. This is
the shear resonance curve, which shows the
maximum amplitude at a characteristic(resonance) frequency. When the upper andlower surfaces are in a large separation, theheight of this resonance peak is sensitive to

530

Figure 5. The device for resonanceshear measurement : a photograph (top)and a schematic drawing (bottom).

the viscosity of confined liquid and decreases with decreasing the surface separation.
When the surfaces come closer, the resonance frequency usually shifts to a higher
frequency due to the coupling of the upper and lower surfaces mediated by confined
liquid (due to the contribution of the spring of the lower unit).
3. Results and discussion
3.1 Linearity and Resolution of Distance Determination by Twin-path SFA
We first examined the linearity in the displacement measurement by the twin pathunit for large displacement range. The movement of a mirror fixed at the end of thesurface drive unit was measured by both of a capacitance probe (ST-0535A, IWATSU
Electric Co., Ltd.) and the twin path unit. The surface drive unit was operated by apulsed motor with a differential spring (see Figure 2). The displacement measured by
the twin path unit and by the capacitance probe well agreed with the calculated value
using the data (0.008 nm/pulse by FECO for this drive system). The deviations between
the measured and the calculated values were ca. 2% for twin-path method and 4% forcapacitance probe over the 5 µm, respectively. The measurements by the twin path unit
showed higher accuracy and linearity than the capacitance probe used in this study.
In order to examine the resolution of displacement measurement by the twin pathmethod, the stepwise motion of
mirror was given by the pulse motor
was monitored. The mirror surface
was moved by 1 nm (pulse counts,
200; velocity, 400 counts/s) every 5
seconds interval and the total
displacement was measured every
second. Figure 6 plots the data at
every second together with thecalculated value based on the given Figure 6.
The displacements in air
pulses. The measured data agreed measured by the twin path method (solid
well with the estimated value, and line) compared with the calculated value
from the pulse number of motor (dotted
the resolution of a current set-up isline).
0.2 nm, which is close to theresolution by FECO (0.1 nm).
3.2 Double Layer Force between Mica Surfaces Measured by Twin-path SFA
In order to demonstrate the reliability of the apparatus, we performed typical

631

measurements. The surface forces
between mica surfaces in aqueous
KBr (MERCK, suprapur) (0.1 mM,
1.0 mM and 10.0 mM) were
measured by injecting the KBrsolution into the chamber. Thesesurface force profiles are plotted in
Figure 7. The decay lengths of 32 ±3 nm, 11 ± 1 nm, 4 ± 1 nm for 0.1
mM, 1.0 mM and 10.0 mM, Figure 7. Surface forces between mica
surfaces in aqueous KBr solution. The
respectively, were well agreement
solid triangles, open squares, and solidwith the theoretical Debye lengths squares are the profiles of 0.1 mM, 1.0 mM(30.4 nm, 9.6 nm, 3.0 nm) [1]. The and 10.0 mM KBr solutions. The broken
brokenlines
indicated
the lines denote the theoretical DLVO curves
at constant surface potential and constanttheoretical fits to DLVO forces of surface charge conditions.
the constant surface potential (0.1mM, 90 mV; 1.0 mM, 90 mV; 10.0
mM, 50 mV) and constant surface
charge (0.1 mM, 0.02 charge/nm2;
1.0 mM, 0.06 charge/nm2; 10.0
mM, 0.08 charge/nm2) conditions.
The pull-off force was detected
only in 0.1 mM KBr solution as
2.6 ± 1.6 mN/m. These results arewell agreement with previous
results
measuredbytheFigure 8. Resonance curves for NaCl
conventional SFA[1,2].
solution (7 mM) confined between mica
surfaces at seven distances: 345.9 nm,
3.3
Aqueous NaCl Solution 1.8 ± 0.3 nm (load = 0.14 mN), 1.1 ± 0.3
Conﬁned between Mica Surfaces nm (0.24 mN), 0.6 ± 0.3 nm (0.55 mN),
0.5 ± 0.2 nm (1.33 mN), 0.3 ± 0.2 nm (2.15
Measured by RSM.
mN), 0.0 ± 0.3 nm. The reference states of
The dynamics of conﬁned water the separation and mica-mica contact in air
thinner than a few nanometers are shown together. The arrows denote thewere in controversial in previous peak position of the resonance curve at thesurface distances. The solid lines denotestudies [19, 20].
Our study
the fitting curves to our mechanical model.
employing RSM provided a327

comprehensive picture for this complicated situation[21]. The viscoelasticity of the thinﬁlm of aqueous NaCl solution conﬁned between mica surfaces was measured by shear
resonance apparatus. The observed shear resonance curves (Figure 8) at separations
less than ca. 2 nm indicated that the solution exhibits the high lubrication effects undersome loads. The distances were measured using FECO. The effective viscosity (0:1–
10 Pa s) obtained for the separations less than 1 nm from a mechanical model was 2 – 4
orders of magnitude larger than the bulk value.
3.4 Ionic LIquids Conﬁned between Silica Surfaces Measured by RSM.
Recently, we applied RSM forionic liquids.
Two types ofimidazolium-based ionic liquid (IL),
1-butyl-3-methylimidazoliumbis(trifluoromethanesulfonyl)amide([C 4 mim][NTf2 ]) and 1-butyl-3methylimidazolium
tetrafluoro
borate ([C 4 mim][BF 4 ]), confined
between silica surfaces were
investigated by RSM together withsurface force measurement [22].
The surface force profiles in the ILs
showed oscillatory solvation forces
below the characteristic surface
separations:
10.0
nm
for
[C 4 mim][NTf2 ] and 6.9 nm for[C 4 mim][BF4 ].
The
morepronounced solvation force found in[C 4 mim][NTf2 ] suggests that the
crystalline property of the IL Figure 9.
Resonance curves for (a)contributes to the stronger layering [C4mim][NTf2] and (b) [C4mim][BF4]of the Ils adjacent to the surface. confined between silica surfaces at various
separation distances under applied load N.
The resonance shear measurement
Reference curves for separated in air (AS)
(Figure 9) and the physical model and connected by silica-silica contact (SC)analysis revealed that the viscosities are also shown. Solid lines denote the bestof the confined Ils were 1−3 orders fitting curves on the basis of a physicalmodel [23].
of magnitude higher than that of the338

bulk IL. This study also focused on the correlation between the resonance shear
behaviour and the lubrication property of the Ils, and the suspension rheology in the Ils.
An understanding of the solid-IL interface and of Ils confined in nanospace will
facilitate the further development of novel applications employing Ils.
4. Conclusion
This paper reviews a new surface forces apparatus (twin-path SFA) and resonanceshear measurement, both we have developed recently. With the twin-path SFA, it ispossible to use metals, ceramics and other opaque samples for substrates. They are not
only interesting materials but provide opportunities for broader applications of theforces measurement: for example, we have constructed electrochemical SFA using gold
as electrodes [24]. The twin-path SFA is compact compared with the conventional SFA
using FECO, and easily operated by a computer. Combining with a spectroscope,
spectroscopic SFA for fluorescence lifetime measurement was developed [25].
The properties of confined liquids are different from those of the bulk due to theconfinement effect and the interaction of liquid molecules with the surfaces. They
attract increasing attention because of recent progress in the preparation of many porous
materials including nanotubes and the nano-fabrication processes such as nanoprinting[25]. Shear measurement based on SFA can offer a useful tool for studying confined
liquids. Especially, the resonance method is relatively easy to operate, and applicablefor both nano-rheology and –tribpology. Resonance responses are sensitive to changes
in properties of confined liquids, so it is possible to monitor changes in viscosity,
traction and triblogical properties, and even stick-slip phenomena, which are often
correlated with structural and/or packing properties of liquids. We expect thesemeasurements will be more widely used in material science.

References[1] J. Israelachivili, Intermolecular and Surface forces 3rd ed., (2011).
[2] A. W. Adamson, A. P. Gast. Physical Chemistry of Surfaces 6th ed. New York: John
Willy& Sons (1997).
[3] K. Kurihara, Nano-Surface Chemistry M. Rosoff ed., Marcel Dekker Inc., 1 (2002).
[4] J.-M. Lehn, Supramolecular Chemistry, Weinheim: VCH (1995).
[5] D. V. Talapin, J.-S. Lee, M. V. Kovalenko, E. V. Shevchenko, Chem. Rev. 110, 389(2010).
[6] G. Decher, Science 277, 1232 (1997).

934

[7] J. Israelachvili, H. Wennerstrom, Nature 379, 219 (1996).
[8] G. Reiter, A. L. Demiral, S. Granick, Science 263, 1741 (1994).
[9] M. Mizukami, K. Kurihara, Chem. Lett. 28, 1005 (1999); ibid. 29, 256 (2000).
[10] M. Mizukami, M. Moteki, K, Kurihara, J. Am. Chem. Soc, 124, 12889 (2002).
[11] T. Abe, K. Kurihara, N. Higashi, M. Niwa, J. Phys. Chem. 99, 1820 (1995).
[12] T. Suzuki, Y.-W. Zhang, T. Koyama, D. Y. Sasaki, K. Kurihara, J. Am. Chem. Soc.
128, 15209 (2006).
[13] K. Kurihara, Adv. Colloid Sci. 71-72, 243 (1997).
[14] N. A. Burnham, R. J. Colton. In: D. A. Bonnel, ed. Scanning TunnelingMicroscopy and Spectroscopy. New York: VCH, 191 (1993).
[15] G. V. Lee, L. A. Chrisey, R. J. Colton, Science 266, 771 (1994).
[16] H. Kawai, H. Sakuma, M. Mizukami, T. Abe, Y. Fukao, H. Tajima, K. Kurihara,
Rev. Sci. Instrum. 79, 043701 (2008).
[17] C. Dushkin, K. Kurihara, Rev. Sci. Instrum. 69, 2095(1998).
[18] K. Creath, in Progress in Optics (Ed. by E. Wolf), Elsevier Science Publishers B.
V., 26, 349 (1988).
[19] Y. Zhu and S. Granick, Phys. Rev. Lett. 87, 96104 (2001).
[20] U. Raviv and J. Klein, Science 297, 1540 (2002).
[21] H. Sakuma, K. Otsuki, K. Kurihara, Phys. Rev. Lett. 96, 046104 (2006).
[22] K. Ueno, M. Kasuya, M. Watanabe, M. Mizukami and K. Kurihara, Phys. Chem.
Chem. Phys. 12, 4066 (2010).
[23] M. Mizukami and K. Kurihara, Rev. Sci. Instrum. 79, 113705(2008).
[24] T Kamijo, M. Kasuya, M. Mizukami and K. Kurihara, Chem. Lett., 40, 674 (2011) .
[25] D. Fukushi, M. Kasuya, H. Sakuma and K. Kurihara, Chem. Lett. 40, 776 (2011) .

35
10Bioelectrochemical Imaging with Micro/Nanoelectrode Systems
Tomokazu Matsue1,2, Kosuke Ino2, Yasufumi Takahashi2,3, Andrew I. Shevchuk3,
Pavel Novak3, Yuri E. Korchev3 and Hitoshi Shiku1,2
1
WPI Advanced Institute for Materials Research, Tohoku University,
Sendai 980-8579, Japan
2
Graduate School of Environmental Studies, Tohoku University,
Sendai 980-8579, Japan
3
Division of Medicine, Imperial College London, Hammersmith Hospital Campus,
London, W12 0NN, United Kingdom
1. Introduction
Recently, the development of multipoint measurements and imaging of biomaterials
has received a great deal of attention due to the strong demand for rapid, comprehensive,and high-throughput analyses. These techniques allow simultaneous detection andquantification of multiple analytes. A variety of array-based biosensing systems havebeen developed so far. Most of them are based on fluorescence detection or imaging
because fluorescence measurements typically have high sensitivity and a variety oftools for performing the measurements is commercially available.
However,
fluorescence detection has some disadvantages, such as undesired fluctuations due toquenching or emission from non-target materials, shielding by turbid solution, and theneed to label non-fluorescent species, which may cause toxic side effects during
analyses. As an alternative method, electrochemical detection or imaging has also been
applied for detailed analysis of biomaterials. Array-based electrochemical devices havealso been used for multipoint measurements. The electrochemical signal can beprocessed by conventional electronics in a very cheap and fast manner. Furthermore,miniaturized electrochemical transducers can easily be integrated in a microsystem by
employing conventional microfabrication technologies. In the past decade, various
types of amperometric microelectrode arrays for multipoint measurements andbioimaging have been designed and applied to chemical and biological analyses. Theseelectrochemical array devices have substantial advantages, including rapid responsetime and qualitative and quantitative detection. Scanning electrochemical microscopy(SECM) is also a popular electrochemical imaging system [2]. SECM uses a
micro/nanoelectrode as a scanning probe and provides sample surface electrochemical
property under physiological conditions without physical contact. Because of uniqueproperties SECM has been applied localized electrochemical measurements.

36

In this article, we will describe the recent progresses of electrochemicalmeasurements and bioimaging with integrated micro/nanoelectrde devices. Bioimaging
with scanning electrochemical microroscopy (SECM) with a micro/nanoelectrode probe
will also be reported.
2. Adderable measurement with micro/nanoelectrode devices
Among the various electrochemical arrays, the development of an individually
addressable device for multipoint measurements and bioimaging has been recognized asa key issue to cope with increasing demands for a versatile, reliable and easy-to-use
analytical system, especially for comprehensive screening purposes. However, it isdifficult to collect electrochemical responses at many individual measurement points
using a conventional electrochemical device, because sufficient space for the bond pads
is not available on the chip border. To solve this problem, we have proposed a novel
method to realize individually addressable electrochemical measurement using a device
consisting of two sets of microelectrode arrays.
In the device, column and row electrodes were orthogonally arranged on two
different glass substrates in order to assemble an addressable microelectrode device forthepurposeofcomprehensive
electrochemical detection [3].
Anamperometric signal was separately
detected at the individual crossing points ofthe column and row electrodes on the basisof redox cycling of localized electroactive
species occurring between the electrodes.
Fig. 1. Principle an addressable
The addressable microelectrode device was
microelectrode / microwell array forsimple and could be easily assembled;
comprehensive
electrochemical
however, it comprised as many as 10 × 10
analysis.
addressable detection points on a single
chip. The basic electrochemical performance of the device was investigated by using
the ferricyanide/ferrocyanide redox couple.
Electrochemical responses at 100
individual points could be collected within 22 s. The present device was successfully
used for imaging the spots of alkaline phosphatase on the array substrate. The results
indicate that the device can be applied to comprehensive and high-throughput detection
and imaging of biochemical species.
A microwell array was further incorporated into the addressable device to conduct
high-throughput screening of bioparticles and genetically engineered cells

37accommodated in the wells [4]. We demonstrate the rapid electrochemical detection of
the reporter protein—secreted alkaline phosphatase (SEAP)—from a single geneticallyengineered HeLa cell (HeLa-pSEAP) using the addressable microelectrode/microwellarray device. Figure 1 shows the operation principle of detection of the reporter proteinwith the addressable device. The HeLa-pSEAP cells that secrete ALP were randomly
seeded in the microwells and the amplified current was detected. The reduction current
for the microwell with a single HeLa-pSEAP cell increased with time, while nomeaningful response was detected for the empty wells. These results indicate that
SEAP secreted from the cell catalyzes the hydrolysis of PAPP to produce PAP, which isaccumulated in the well.
Figure 2 shows an image of the
reduction current of each microwellafter 20 min of incubation time. The
responses in the empty microwell is0.754 ± 0.996 pA while in cell
occupied microwell is 16.3 ± 5.49 pA.
Figure 2(c) shows histogram of thebcurrent responses distribution from thecells, unlike the case for ALP beads,
each single HeLa-pSEAP cell showed adifferent
current
response,
approximately 20 % of the cells show
Fig. 2. a) Scheme of cells in the
responses similar to those observed for c
microwells. The number represents thewild-type cells. These variations in thenumber of cells in each well. b) Imaging
response are due to the differentof the current responses at 10x10
expression levels of ALP frommicrowells. This image was taken 20
individual cells and the size variations
min after the injection of PAPP. c)of single cells. The average amount ofHistogram of the current response
PAP generated from the catalytic
distribution of the cells.
reaction of a single HeLa-pSEAP cell
was calculated from the current
responses and found to be 3.6 × 10–17 mol for an incubation time of 20 min. These
results demonstrate that the present device can be used for highly sensitive and highthroughput screening to detect the protein expression activity of genetically engineered
cells at the single-cell level. Since the ALP has been widely used as a labeling enzyme
and reporter protein, the present device can be used for the screening of a38

comprehensive analysis of DNA, proteins, and cells [5].
3. Bioimaging with micro/nanoelectrodedevices
Although the device described above is very
useful for high-throughput electrochemical
detection, careful assembly of the device isrequired to align two different glass substrates
with the row or column electrodes at exact
locations upon each measurement, which is timeconsuming and results in low reproducibility.
Furthermore, there is no open space on the device
Fig. 3. Images of the 32 × 32
for handling samples such as cells, because thecrossing points and the sensor
sensor areas are surrounded by glass substrates
point.
with electrodes.
In this study, we havedeveloped a new device to solve these problems.
The general architecture, outlined in Fig. 3, provides a means for creating a new
detection system that enables electrochemical detection based on local redox cycling
and 1024 addressable sensor points incorporated into a small area (40 mm2) for thecomprehensive imaging of electrochemical species [6]. Interdigitated array (IDA)
electrodes were incorporated onto glass substrates to arrange a single IDA at eachsensor point of the device. IDA electrodes have two interdigitated comb-type arrays,
each of which consists of planar and parallel metal fingers.9 When the potential of eachcomb-type electrode is appropriately controlled, a species oxidized at an electrodefinger can be reduced back at the neighboring fingers, resulting in redox cycling foramplification of the electrochemicalsignal. In this study, one comb-type
electrodes of the IDA connected to acolumn electrode and the other to arow electrode.
The device was applied forbioelectrochemical imaging of ALP
Fig. 4. Electrochemical imaging of ALP. The
aggregates. The image followed theelectrochemical response was acquired after
position of the ALP aggregate in theadding the ALP/BSA aggregate (approximately 1solution and the intensity was
mm diameter) (right image).
dependent on the ALP activity of theaggregate (Fig. 4).

39

Enzymes, such as ALP, were successfully detected using the device; therefore, thisdevice could be used as a comprehensive, high-throughput lab-on-a-chip tool for
applications such as enzyme-linked immunosorbent assay (ELISA), reporter gene assay
for monitoring gene expressions, DNA analysis, and cell culture array. Although anapplication of electrochemical potentials to electrodes may be a critical issue foradhesive cells and spheroids, it is unnecessary to bound cells on the electrodes of thedevice since the device has microwells that can trap cells or spheroids on the sensors forcell assays.
4. Bioimaging with SECM
SECM has been applied for evaluating the enzyme and cellular activity estimatingcell membrane permeability and detecting electroactive metabolic chemicals with shortlife spans. Membrane protein has also been detected with SECM. Miniaturization of
the probe electrode is important for improving the temporal and spatial resolution. In
addition, a fine distance regulation system is required to approach the probe electrodeagainst live cell surfaces.
Significant efforts have been made to bring the electrode proximate with sample
surface. Nevertheless, it was difficult to apply the system to the measurement of soft
samples because the force interaction was usually very unstable to serve as a feedback
signal. Shear force feedback regulation has also been used for control of the probe
electrode sample distance [7]. We reported the simultaneous imaging of the topography
and electrochemical signals of single living cells using shear force distance regulationof a ring type nanoelectrode probe. However, preventing probe-cell contact was still
difficult because the solution viscosity interfered with the shear force detection. We
adopted the feedback regulation used inscanning ion conductance microscopy(SICM) which uses a nanopipette as ascanning probe. SICM is based on thephenomenon that the ion flow through asharp fluid filled nanopipette is partiallyoccluded when the nanopipette approaches
the surface of a sample. Living cell surface
topography and dynamic measurements have
Fig. 5. SEM micrographs of the
been performed. Topographical information
SECM/SICM probe.
of the live cell surface can be used to improve
the resolution of other analytical tools [8].

40

We demonstrate a hybrid system of A
scanning electrochemical microscopy (SECM)
B
and SICM with ion current feedback nano-positioning control for simultaneous imaging
of non-contact topography and spatial distribution electrochemical species [9]. A
nanopipette/nanoring electrode probe provided submicron resolution of theelectrochemical measurement on surfaces with complex topology. The SECM/SICM
pipette had an aperture radius of 220 nm. The inner and outer radii of the SECM Au
ring electrode were 330 and 550 nm, respectively (Fig. 5). Characterization of theDCprobe was performed with scanning electron microscopy (SEM), cyclic voltammetry,
and approach curve measurements. SECM/SICM was applied to simultaneous imaging
of topography and electrochemical responses of enzymes (horse radish peroxidase(HRP) and glucose oxidase (GOD)) and single live cells (A6 cells, SCG cells, andcardiac myocytes). The measurements revealed the distribution of activity of the
enzyme spots on uneven surfaces with sub-micrometer resolution. SECM/SICM
Fig. 6.images
Topographic(A,C) together
and electrochemicalacquired high resolution topographicof cells
with theimages
map of(B,D) combinedof a GOD immobilized
and lower
electrochemical signals (Fig. 6). This
technique substrate.
was alsoUpper
appliedto theimages werespecies
capturedthroughwith 8 μm
× 8 μmmembranes.
and 2 μm × 2 μm,
evaluation of the permeability of electroactive
cellularrespectively. The probe-sample distances were held at 100
nm.
Summary
Bioelectrochemical sensing systems with micro/nanoelectrodes has been applied to
localized characterization of biomaterials. The results so far obtained clearly indicatethat electrochemical measurements afford indispensable information particularly onelectron and ion-transfer at various biomolecules-related interfaces. Also, incorporationof modern micro/nanofabrication technologies into electrochemical devices will leadunique bioelectronics devices which ensure the realization of safe and secure society.

References[1] S. Szunerits, and L. Thouin, “Microelectrode array” in “Handbook ofElectrochemistry”, Elsevier (2007).
[2] A. J. Bard and M. V. Mirkin, “Scanning Electrochemical Microscopy”, Marcel
Dekker (2000).
[3] Z. Y. Lin, Y. Takahashi, Y. Kitagawa, T. Umemura, H. Shiku, T. Matsue, Anal.
Chem., 80, 6830 (2008)[4] Z. Y. Lin,Y. Takahashi, T. Murata, M. Takeda, K. Ino, H. Shiku, T. Matsue,
Angew. Chem. Int. Ed., 48, 2044 (2009)

[5] Z. Y. Lin, K. Ino, H. Shiku, T. Matsue, Chem. Commun., 46, 559 (2010); Z. Y.
Lin, K. Ino, H. Shiku, T. Matsue, G. Chen, Chem. Commun., 46, 234 (2010).
[6] K. Ino, W. Saito, M. Koide, T. Umemura, H. Shiku, T. Matsue, Lab Chip, in press[7] Y. Takahashi, T. Miyamotoa, H. Shiku, R. Asano, T. Yasukawa, I. Kumagai, T.
Matsue, Anal. Chem., 81, 2785 (2009); Y. Takahashi, H. Shiku, T. Murata, T.
Yasukawa, T. Matsue, Anal. Chem., 81, 9674 (2009)[8] Y. Takahashi, Y. Murakami, K. Nagamine, H. Shiku, S. Aoyagi, T. Yasukawa, M.
Kanzaki, T. Matsue, Phys. Chem. Chem. Phys., 12, 1001 (2010)[9] Y. Takahashi, A. I. Shevchuk, P. Novak, Y. Murakami, H. Shiku, Y. E. Korchev, T.
Matsue, J. Am. Chem. Soc., 132, 10118 (2010)42

Nanoporous Metals as Green Catalysts for Molecular Transformations
Naoki Asao
WPI Advanced Institute for Materials Research, Tohoku University
1. Introduction
Molecular metal catalysts (A), such as AuCl(PPh 3 ) and Pd(PPh3 ) 4 , have been used
for many molecular transformations as homogeneous catalysts [1]. However, the use ofheterogeneous catalysts offers several advantages over homogeneous systems, such asease of recovery and recycling, atom utility, and enhanced stability. While bulk metals(D) are catalytically inert materials, supported nanoscale metal particles (B) on suitable
oxide show catalytic activities in a variety of molecular transformations [2]. On theother hand, the catalytic properties of unsupported metals, such as nanoporous metalmaterials (C), are still less explored. The nanoporous metal materials can be generally
prepared by leaching less noble metals from the corresponding alloys through a routesimilar to that for the preparation of Raney nickel. For example, nanoporous gold isfabricated from Au-Ag alloy by means of free corrosion in nitric acid [3]. It has an open
sponge-like morphology of interconnecting ligaments on the nanometer length scale.
Our research focused on these nanoporous metal materials as promising green catalysts.

Au molecular catalyst

Au nanoparticle

Nanoporous Au

Bulk Au metal

Pd molecular catalyst

Pd nanoparticle

Nanoporous Pd

Bulk Pd metal

A

B

C

D

Fig. 1 Four different types of morphology of gold and palladium.
2. Results and discussion
2.1 AuNPore-catalyzed benzannulation
We initially examined the catalytic activity of the nanoporous gold by use of the43[4+2] benzannulation reaction between ortho-alkynyl benzaldehyde 1 andphenylacetylene 2 as a model reaction, which has been previously reported by our groupwith homogeneous gold catalysts [4]. The reaction proceeded with 20 mol % of
AuNPore-1, having around 25 nm pore size, at 150 oC for 2.5 h, and the desired product3 was obtained in 62 % yield together with a small amount of decarbonylated
naphthalene derivative 4 (Scheme 1). On the other hand, any reactions did not takeplace in the absence of the catalyst or in the presence of the non-dealloyed Au 30 Ag 70
thin plates. These results clearly indicated that the nanoporous structure of the catalyst
is necessary for this transformation [5].
H

CHO

AuNPore (20 mol %)+Ph

o-C6H4Cl2, 150 oC, 2.5 h
1

Ph

Ph 2
Entry
1
2
3
4
5
6
7

3
Average pore size
AuNPore-1
reuse 1
reuse 2
AuNPore -2
AuNPore -3
AuNPore -4
AuNPore -5

25 nm
30 nm
40 nm
60 nm
100 nmO

Ph

Yield of 3 (%)
62
61
60
61
12
trace
0

Scheme 1 AuNPore-catalyzed benzannulation reaction between ortho-alkynyl
benzaldehyde 1 and phenylacetylene 2.
AuNPore can be recovered simply by picking up with tweezers because the catalyst
is a bulk metal. Therefore, unlike ordinary heterogeneous catalysts, any cumbersome
work-up procedures, such as filtration or centrifugation, are not required. The catalyst
can be reused several times and the chemical yields of 3 were constantly good in eachcase (entries 1-3). We found that the catalytic activity of the nanoporous gold washighly dependent on the pore size in this transformation. AuNPore-2, having around 30
nm pore size, exhibited the similar activity with AuNPore-1 (entry 4). However, thechemical yields were dramatically decreased with catalysts having more than 40 nm
pore sizes (entries 5-7).
2.2 AuNPore-catalyzed oxidation of organosilanes with water
These results mentioned above prompted us to further explore the feasibility of44

carrying out a wide range of molecular transformations with this material. Then, we
next examined the oxidation of organosilanes with water, leading to silanols, which areuseful building blocks for silicon-based polymeric materials as well as nucleophilic
coupling partners in organic synthesis. Although several metal particles have beenreported as catalysts for this transformation, there are some drawbacks in those cases,
such as poor long-term stability, narrow substrate generality, formation of by-products,
and complicated work-up procedure for separation of products from the catalyst [6]. We
found that the nanoporous gold exhibited a remarkable catalytic activity in the oxidationof PhMe 2 SiH 5 and the corresponding silanol 6 was produced quantitaively under mild
conditions together with the evolution of hydrogen gas (Scheme 2) [7]. The formationof by-products, such as disiloxane, was not detected at all by GCMS. The turnover
frequency (TOF) of 3.0 s–1 was achieved in this catalytic system. The catalyst can beused at least 5 times repeatedly and the product was obtained nearly quantitatively
every time (entries 1-5). The turnover number (TON) reached up to 10700. SEM
images of the AuNPore catalyst (Fig. 2) indicate that there is no difference on thesurface of the catalyst before and after 5 times use.

PhMe2Si H
5

+

H2O

AuNPore (1 mol %)acetone, rt, 1 h

PhMe2Si OH

+

H2

6

Entry

Catalyst

Yield of 6 (%)

1
2
3
4
5

f reshreuse 1
reuse 2
reuse 3
reuse 4

100
98
100
99
100

Scheme 2 AuNPore-catalyzed oxidation of PhMe 2 SiH with water.
(a)

(b)

Fig. 2 Scanning electron microscopy (SEM) images of AuNPore: a) before reaction, b)
after being used five times for oxidation of PhMe 2 SiH.

45

The catalytic oxidation reactions with a variety of organosilanes were conducted andrepresentative examples are shown in Fig. 3. Not only aromatic silanes but also
sterically hindered trialkylsilanes were oxidized effectively. The AuNPore catalyst wasalso applicable to the oxidations of tri-, di-, and mono-phenylsilanes, and thecorresponding oxygenated products were obtained in high yields, respectively. Alkenyland alkynyl-containing silanes were oxidized smoothly without reduction of theirmultiple bonds by H 2 gas.
Bu3SiOH

iPr3SiOH

Ph3SiOH

Ph2Si(OH)2

PhSi(OH)3

95 %

88 %

99 %

90 %

80 %

Me
Ph Si OH
98 %Ph

SiMe2OH
92 %Fig. 3 Representative examples for AuNPore-catalyzed oxidation of organosilanes.
Leaching test was conducted to clarify whether the disolved gold species in solventstake part in the current reaction system or not. After the catalytic oxidation of 5 was
carried out for 10 min under the standard condition, AuNPore catalyst was removed
from the reaction vessel. 1H NMR analysis of the mixture showed that 6 was produced
in 48% yield at this time. While stirring of the mixture was continued in the absence ofthe catalyst for 50 min, further consumption of 5 was not detected at all. Then, the
AuNPore was put back into the mixture. The oxidation reaction started again and finally
6 was obtained in 99% yield with 50 min. Furthermore, leaching of the gold in thereaction of 5 was not detected by inductively coupled plasma (ICP) analysis(<0.0005%). These results clearly indicated that the current transformation was
catalyzed by the AuNPore catalyst but not by the dissolved gold species in solvents.
2.3 PdNPore-catalyzed Suzuki coupling
In parallel with the study on AuNPore, the catalytic property of nanoporous
palladium (PdNPore) has been investigated. This material can be easily fabricated frommetallic glassy ribbons Pd 30 Ni50 P 20 [8] by electrochemical dealloying process [9]. The
resulting PdNPore was used as a catalyst in the Suzuki-coupling reaction, which is oneof the most important organic transformations in recent years [10]. The reaction ofiodobenzene 7 with p-tolylboronic acid 8 using KOH as a base in the presence of 2
mol% PdNPore gave the corresponding biphenyl product 9 in a nearly quantitative yield46

(Scheme 3, Entry 1). On the other hand, no coupling products were obtained in thepresence of un-dealloyed (non-porous) metallic glass Pd 30 Ni50 P 20 or in the absence of
PdNPore [11].
Me

Me

I

PdNPore (2 mol %)+7(HO)2B

KOH, MeOH
50 oC, 3 h

8

9

Entry

Catalyst

Yield of 9 (%)

1
2
3
4

f reshreuse 1
reuse 2
reuse 3

99
94
92
95

Scheme 3 PdNPore-catalyzed Suzuki-coupling reaction.
Recently, small palladium particles, consisting of gathering of palladium atoms, havebeen used as a solid state catalyst. However, a drawback of this catalyst is that it
undergoes quite easy agglomeration under the reaction conditions, leading todeactivation of the catalyst. Hence, appropriate stabilizer or supporter is necessary to
prevent deactivation by agglomeration. In contrast, PdNPore exhibited an excellent
catalytic activity under mild reaction conditions without any supporter, ligand, or
stabilizer. Although palladium black has been reported as an unsupported catalyst for
Suzuki coupling reaction, nearly one-half equivalent of catalyst is necessary probably
due to the poor catalytic activity. Recovery of ordinary heterogeneous catalysts often
requires complicated treatment. In contrast, the recovery process in the current catalytic
system is simple. Since the size of the catalyst is relatively large, the catalyst and the
product can be separated easily by just removal of the liquid moiety by a pipette. The
recovered catalyst was washed with MeOH several times and it was reused without
further purification. Indeed, the product 9 could be obtained in excellent yield every
time when the reactions were performed 4 times repeatedly. Furthermore, SEM imagesof the catalyst before and after 4 times run indicated the nanoporous structure wasmaintained well (Fig. 4).
(a)

(b)

Fig. 4 Scanning electron microscopy (SEM) images of PdNPore: a) before reaction, b)
after being used four times for Suzuki coupling between 7 and 8.

47Since leaching of toxic palladium causes contamination of the final products with thedissolved palladium, catalytic systems with low leaching are highly desirable.
Inductivity coupled plasma (ICP-AES) analysis did not detect the leaching of thepalladium (< 0.0005%) during or after reaction of 7 with 8. We next checked theleaching by conducting the reaction with the supernatant as follows: The reaction of 7with 8 was carried out for 30 min under the standard condition, then a half amount ofsolution was picked up. 1H NMR analysis of the supernatant indicated that 9 was
produced in 3% yield at this time. The supernatant was stirred in the absence of thecatalyst for 3 h; the chemical yield of 9 at this moment was 24%. On the other hand,stirring of the residual reaction mixture having the catalyst for 3 h gave 9 in 93% yield.
These results clearly indicated that dissolved Pd species existed and catalyzed thereaction but its activity was much lower than that of solid state of the catalyst due to the
low leaching amount.
The Suzuki-coupling reactions using various aryliodides and arylboronic acids were
examined and representative examples are shown in Fig. 5. The reaction proceededsmoothly even with sterically hindered 2-iodoanisole. The reactions of aryl iodidespossessing electron-withdrawing groups proceeded faster than those having electrondonating groups. In contrast, the reactions of arylboronic acids possessing electrondonating groups proceeded faster than those having electron-withdrawing groups. Not
only aryl iodides but also aryl bromides are suitable substrates.
I

I

I

I

Ar1 I
OMe

MeO

Me
Ar2 B(OH)2
Yield (%)MeOMe(HO)2B(HO)2B
6 h, 79 %Ac

F3C

1 h, 83 %(HO)2B
0.5 h, 99 %Me(HO)2B
2 h, 95 %Fig. 5 Representative examples for PdNPore-catalyzed Suzuki coupling.
2.4 PdNPore-catalyzed Heck reaction
The material was next applied to Heck reaction, which is widely utilized in organic
synthesis from small scale to the industrial process (Scheme 4) [12]. The reaction ofiodobenzene 7 with acrylic acid 10 using KOH as a base in the presence of 2 mol % of
PdNPore gave cinnamic acid 11 in 84 % yield (Entry 1). Addition of tetra-nbutylammonium iodide (TBAI) improved the chemical yield up to 94% (Entry 2). Since
TBAI is known as a stabilizer of Pd particles, it might stabilize the dissolved Pd species

48

even in the case of the current catalytic system. On the other hand, no coupling products
were obtained at all in the absence of PdNPore catalyst or in the presence of undealloyed metallic glass Pd 30 Ni50 P 20 ribbon [13].
I
CO2H

+
7

CO2H

PdNPore (2 mol %)KOH, MeOH
80 oC, 20 h

10

11

Entry

Additive

Yield of 11 (%)

1
2

TBAI

84
94

Scheme 4 PdNPore-catalyzed Heck reaction.
Not only aryliodides, but also less reactive arylbromides were suitable substrates byusing Köhler’s condition (Scheme 5) [14]. Treatment of 4-bromoacetophenone 12 withstyrene 13 in the presence of 2 mol % of PdNPore in N,N-dimethylacetamide (DMAc)
resulted in the formation of 14 in a nearly quantitative yield (Entry 1). Heck reaction iswell known to be catalyzed by Pd/C, which is one of the most accessible heterogeneous
Pd catalysts. However, it has a serious limitation on the recyclability [14]. In contrast,
our catalyst can be used at least 5 times. SEM analysis of the catalyst clearly indicatedthat nanoporous structures were maintained well even after 5 runs. Furthermore, any
significant changes of the composition of the catalysts were not observed before andafter reaction by energy-dispersive X-ray (EDX) analysis. These results clearly indicatethat PdNPore is a robust and recyclable catalyst for Heck reaction.
Br
+

Ph

PdNPore (2 mol %)13

NaOAc, DMAc
140 oC, 12 h

Ac
12

Ph
Ac
14

Entry

PdNPoreYield of 14 (%)

1
2
3
4
5

Fresh
Reuse 1
Reuse 2
Reuse 3
Reuse 4

99
99
99
99
99

Scheme 5 PdNPore-catalyzed Heck reaction of bromoarene.
The representative examples are shown in Fig. 6. While the reactions of aryliodides
were not influenced significantly by the electronic effect of the substituents on thearyliodides, the reaction speed of arylbromides was considerably dependent on the49substituents on bromoarenes.
CO2H
Ar

CO2H

CO2H

I + 10 :MeMeO

24 h, 99 %Cl
24 h, 95 %Ph

24 h, 95 %Ph

Ph

Ar Br + 13 :MeO

F3C
20 h, 92 %72 h, 80 %48 h, 93 %Fig. 6 Representative examples for PdNPore-catalyzed Heck reaction.
We compared the leaching amount of Pd from PdNPore, Pd/C, and Pd black catalysts
in the reaction of 12 and 13 by inductivity coupled plasma mass spectrometry (ICP-MS).
On the basis of the average of specific surface areas of these catalysts, the leachingamounts of Pd per unit surface area can be calculated and the results are summarized inTable 1. Obviously, the leaching amount from the PdNPore catalyst is significantly
smaller than those from the other two commercially available catalysts. This resultclearly indicated that PdNPore has higher resistant property against leaching than theother two catalysts. Köhler reported that the Pd concentration in solution in the Pd/Ccatalyzed reaction was highest at the beginning of the reaction and was a minimum atthe end of the reaction by the reprecipitation of Pd onto the support [14]. It is worth
mentioning that the leaching amount from the unsupported PdNPore is smaller than thatfrom the supported Pd/C even at the end of the reaction.
Table 1 Leaching amount of Pd at the end of the reaction with 12 and 13 by use of Pd
NPore, Pd black, and Pd/C catalysts.
Pd catPdNPorePd black
Pd/C (10 wt%)

Leaching amountin solution [µg]Average of specificsurf ace area [m2/g]

Leaching amount perunit surf ace area [µg/m2]

0.57
3.80
48.2

13
50
83

43.8
76.0
580.7

3. Summary
We have demonstrated that nanoporous gold and palladium are promisingnanostructured skeleton catalysts for molecular transformations. Any supports, ligands,
or stabilizers are not required in these catalytic systems. The catalysts can be easily

50

recovered by simple separation processes and the recovered catalysts were reusable
without significant loss of catalytic activities. The exploration of new catalytic
properties of a variety of nanoporous metals as well as designing and creation of novel
types of nano-structured skeleton catalysts are in progress.

Acknowledgements
The author is grateful to Y. Yamamoto, S. Tanaka, M. Chen, W. Zhang, and A. Inouefor their collaboration in this work.
References
1. (a) A. S. K. Hashmi. Chem. Rev. 107, 3180 (2007); (b) N. T. Patil, Y. Yamamoto.
Chem. Rev. 108, 3395 (2008); (c) Y. Yamamoto. J. Org. Chem. 72, 7818 (2007);(d) A. S. K. Hashmi. Angew. Chem. Int. Ed. 49, 5232 (2010); (e) L. Yin, J.
Liebscher. Chem. Rev. 107, 133 (2007); (f) Y. Tsuji, T. Fujihara. Inorg. Chem. 46,
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(a) C. Della Pina, E. Falletta, L. Prati, M. Rossi. Chem. Soc. Rev. 37, 2077 (2008);(b) A. Corma, H. Garcia. Chem. Soc. Rev. 37, 2096 (2008); (c) M. Seki. Synthesis
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3.

(a) A. J. Forty. Nature 282, 597 (1979); (b) J. Erlebacher, M. Aziz, A. Karma.
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4.

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6.

7.
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Soc. 125, 10921 (2003); (c) N. Asao. Synlett, 1645 (2006).
N. Asao, Menggenbateer, Y. Seya, Y. Yamamoto, M. Chen, W. Zhang, A. Inoue.
Synlett in press (DOI: 10.1055/s-0031-1289527).
(a) K. Mori, M. Tano, T. Mizugaki, K. Ebitani, K. Kaneda. New J. Chem. 26, 1536
(2002); (b) E. Choi, C. Lee, Y. Na, S. Chang. Org. Lett. 4, 2369 (2002); (c) T.
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Chem. Int. Ed. 47, 7938 (2008); (d) B. P. S. Chauhan, A. Sarkar, M. Chauhan, A.
Roka. Appl. Organomet. Chem. 23, 385 (2009); (e) T. Mitsudome, A. Noujima, T.
Mizugaki, K. Jitsukawa, K. Kaneda. Chem. Commun. 5302 (2009).
N. Asao, Y. Ishikawa, N. Hatakeyama, Menggenbateer, Y. Yamamoto, M. Chen,
W. Zhang, A. Inoue. Angew. Chem. Int. Ed. 49, 10093 (2010).
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(2008).

51

9.

Y. Zeng, N. Nishiyama, T. Wada, D. Louzguine-Luzgin, A. Inoue. Mater. Trans.

47, 175 (2006).
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Suzuki. J. Organomet. Chem. 576, 147 (1999); (c) S. Kotha, K. Lahiri, D.
Kashinath. Tetrahedron 58, 9633 (2002); (d) F. Bellina, A. Carpita, R. Rossi.
Synthesis 2419 (2004); (e) A. Suzuki. In Modern Arene Chemistry (D. Astruc, ed.),p. 53. Wiley-VCH, Weinheim (2002).
11. S. Tanaka, T. Kaneko, N. Asao, Y. Yamamoto, M. Chen, W. Zhang, A. Inoue. Chem.
Commun. 47, 5985 (2011).
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7449 (2001); (b) A. B. Dounay, L. E. Overman. Chem. Rev. 103, 2945 (2003); (c)F. Alonso, I. P. Beletskaya, M. Yus. Tetrahedron 61, 11771 (2005).
13. T. Kaneko, S. Tanaka, N. Asao, Y. Yamamoto, M. Chen, W. Zhang, A. Inoue. Adv.
Synth. Catal. 253, 2927 (2011).
14. (a) K. Köhler, R. G. Heidenreich, J. G. E. Krauter, J. Pietsch. Chem. Eur. J. 8, 622(2002); (b) R. G. Heidenreich, J. G. E. Krauter, J. Pietsch, K. Köhler. J. Mol. Catal.
A Chem. 182-183, 499 (2002).

52

Exploring new spintronics materials via investigation of fast
precessional spin dynamics using an ultrashort pulse laser
Shigemi Mizukami and Terunobu Miyazaki
WPI Advanced Institute for Materials Research, Tohoku University
1. Introduction
Since the discovery of giant magnetoresistance (GMR) by P. Grünberg and A. Fert
[1,2] who obtained the Nobel prize in 2007, spintronics research field increased year by
year. One big breakthrough is a finding of large tunnel magnetoresistance (TMR) at
room temperature in magnetic tunnel junctions (MTJs) in 1995 [3,4]. The MTJs consistof a few nano meter thick insulating barrier sandwiched by ferromagnetic layers andexhibit, basically, a larger (smaller) resistance in parallel (anti-parallel) configuration ofmagnetizations. This implies that a MTJ can be used for a non-volatile magnetic
random access memory (MRAM) element if a high or low resistance states is regarded
as “1” or “0” digital memory bit.
Another interesting proposal was brought in 1996 into spintoronics is the so-called
spin-transfer-torque (STT) effect [5]. Conducting electrons flowing through a fixedmagnetic layer in a magnetoresistive device are spin polarized along the magnetization.
When these spin-polarized electrons pass through another magnetic layer, thepolarization direction may have to change depending on relative orientation. In thisprocess, the magnetic layer experiences a torque associated with the transfer of spin
angular momentum from conducting electrons. For large current, the spin torqueamplifies the cone angle of spin precession and leads magnetization switching in thecase that the spin torque overcomes magnetic damping. Thus, the magnetization of
nano-scaled free layer is controllable by the flowing current direction.
Nowadays, the researchers in spintronics field are developing STT-MRAM utilizing
the above two fundamental technologies. The features of STT-MRAM is not only nonvolatility but also a large memory capacity and a high speed in reading and storing ofdigital memory, comparable to a dynamic random access memory (DRAM) and/or
static RAM (SRAM), made of CMOS technology [6]. STT-MRAM is considered to be
an important element of Normally-off computer as Green Technologies in near future.
However, there are many subjects to be overcome for realization of such an ultimate
memory. One of the important subjects is to develop the new magnetic materials withlow magnetic damping as well as high perpendicular magnetic anisotropy, and also toclarify their mechanism.

53

2. Perpendicular magnetic anisotropy and magnetic damping
When the magnetic materials are patterned into several tens nano meter scale, that iscomparable to the current CMOS technology node, magnetization direction fluctuates
randomly against time, like as the Brownian motion of very small particle. Reducing ofthese thermal fluctuations of magnetization is crucial to make nano scaled memory
because the thermal fluctuation of magnetization leads to lose a stored digital memoryin MRAM. To avoid it, a magnetic material with a large perpendicular magnetic
anisotropy is used in electrodes of MTJ. Thermal fluctuation of magnetization isstabilized significantly by high perpendicular magnetic anisotropy [7]. There have been
several magnetic materials with high perpendicular magnetic anisotropy, so far, becausesuch materials are also used in a storage media in hard disk drive or permanent magnet.
Most of such magnetic materials have crystal structures with symmetry lower than a
cubic, i.e., tetragonal or hexagonal. Artificial magnetic multilayer also shows
perpendicular magnetic anisotropy owing to two dimensional structures [7]. Most ofthem contain various rare earth or noble metals. History of research on magnetic
anisotropy is long [8] and the development of precise ab-initio calculation and progressof microscopic characterization based on X-ray reveals the mechanism of anisotropy inlast two decade, but physics of magnetic anisotropy was not so clear yet.
In the elementary mechanics, we learn that a friction forces to stop an object moving
in the air and this friction force is proportional to velocity of moving object. Suchfriction is a universal phenomenon that appears from microscopic to macroscopic scale.
Large friction needs large power to drive the motion of object, but a finite friction isnecessary to control it, thus friction control is very important technology to save theenergy, as seen in a hybrid car. Similarly, magnetization also feels a friction insidemagnets, so-called magnetic damping. In STT-MRAM, small magnetic friction isefficient to drive the magnetization motion with saving the power requiring
magnetization reversal [6]. Origin of magnetic friction can be attributed to one electron
spin relaxation phenomena related quantum-mechanical spin-orbit interaction [9], butthere are a few data of magnetic damping in the magnetic materials with perpendicularmagnetic anisotropy and the related physics is not yet understood fully.
Theories show magnetic friction and magnetic anisotropy originates from spin-orbit
interaction, namely materials with large magnetic anisotropy might tend to show large
magnetic friction. Therefore, it is a challenging task to explore new materials suitable to
STT-MRAM.

54

3. Spin dynamics and all-optical time-resolved magneto-optical Kerr effect
The objectives of our studies are to get insight into physics of magnetic damping inmagnetic materials with large perpendicular magnetic anisotropy and also to explore
magnetic materials with both high perpendicular magnetic anisotropy and small
magnetic damping. However, it is difficult to evaluate magnetic damping constant insuch magnetic materials. A basic motion of spin in magnets is precession, which issimilar to oscillation of a pendulum. Precession frequency is roughly proportional to theperpendicular magnetic anisotropy field. Precession frequency is several GHz for theusual ferromagnetic metals, e.g., iron, but it exceeds more than 100 GHz in themagnetic materials with high perpendicular magnetic anisotropy. “All optical pumpprobe detection” is the current state of art technique for the investigation of spin
dynamics [10]. All optical pump-probe detection is based on pump-probe techniquewith femto second laser. The motion of spins can be induced only by laser light pulse
and any coils or inductances, which are required to generate pulsed magnetic field in theother techniques, are not involved in the set-up, so that one can achieve the ultimate
time resolution better than hundred femto second. The equivalent frequency bandwidthof this measurement is more than 1 THz.
In 2008-2009, we have constructed the set-up of all-optical time-resolved magnetooptical Kerr effect (TRMOKE) using a standard optical pump-probe set-up with Ti:
Sapphire laser and regenerative amplifier (wavelength of 800 nm, pulse width less than
100 fs) [11,12]. S-polarized probe light is normally incident on a film surface. A verysmall amount of rotation of polarization vector of laser light reflected from sample is

(a)

(b)

electromagnet
sampleTi:sapphire+
Regenerative amp.

detector
BS

P
WP
λ/2

P
chopper

Figure 1. (a) Schematic illustration of optical set-up. P, WP, and BS correspond to apolarizer, beam splitter, and Wollaston prism as an analyzer. Thin and bold red lines areprobe and pump beam path, respectively. (b) the photograph of optical set-up
constructed in Integration laboratory in WPI-AIMR.

55

detected by a balanced detector after passing though analyzer (Wollaston prism) bypolar magneto-optical Kerr effect (PMOKE). Intense pump beam is also focused to thesample overlapped and delayed by probe beam and time variation of magnetization was
detected. Magnetic field can be applied up to 10 kOe and the field direction can bevaried from in-plane to out-of-plane. Hereafter, we discuss the result of investigation of
fast spin precession dynamics in various magnetic films with large perpendicularmagnetic anisotropy.
5. Precessional spin dynamics in ultrathin films and multilayers exhibiting a large
perpendicular magnetic anisotropy
As mentioned earlier, artificial layered materials have a large uniaxial magnetic
anisotropy induced by symmetry broken at an interface. We investigated Co-based
multilayered structure: Co/Pd [13] and Co/Ni [14], here we show representative resultsof very thin Co layer sandwiched by Pt layer [15].
Films were deposited on a naturally oxidized Si substrate using an ultra-high vacuum
magnetron sputtering system at room temperature. Thickness of buffer and capping
layer of Pt were 5 and 2 nm, respectively, and Co layer thickness was varied from 4 to(c)

MOKE signal (arb. unit)H⊥film(a)

Coercivity (Oe)

400

(b)
300
H⊥film

200
100
0
0

0.5

1.0

1.5

2.

0
-0.1
-0.2
-0.3

dCo (nm)
0.7

0
-0.1
-0.2
-0.3
0
-0.1
-0.2

0.8

0.9

0
-0.1
-0.2
-0.3

1.0

0
-0.1
-0.2
-0.3
0
-0.2
-0.4
-0.6
0
-0.2
-0.4
-0.6
0

1.5

2.0

4.0

100

200

Pump-probe delay time (ps)dCo (nm)

Figure 2 (a) Typical hysteresis curves for a Pt/Co/Pt trilayer film with Co layer
thickness dCo of 0.8 nm. (b) Co layer thickness dependence of Coercivity, and (c) timeresolved magneto-optical Kerr effect signal for the films with different dCo.

56

0.5 nm. A typical hysteresis loop for a film with Co layer thickness of 0.8 nm is shownin Fig. 2(a), in which a coercivity H C was ~ 300 Oe and an effective perpendicularmagnetic anisotropy field H k eff was 2.1 kOe. Figure 2(b) shows the coercivity as afunction of Co layer thickness evaluated from PMOKE measurements, confirming that
Pt/Co/Pt films was magnetized perpendicularly at Co layer thickness d Co < 1 nm. Timeresolved magneto-optical signals for these films are shown in Fig. 2(c). Signal shows arapid decrease in sub-ps time regime and then exhibits damped oscillation, thosecorrespond to ultrafast demagnetization due to pulse heating and magnetization
precession, respectively. Spin precession signals are observed clearly in all films,
especially in case of perpendicularly magnetized films where cobalt layer thickness iscomparable to a few atomic layers. Precession signal decays more rapidly in a filmwith thinner Co layer thickness, which implies magnetic friction acts more strongly on
spins in a few atomic layers of cobalt. To determine magnetic damping quantitatively,
the precession frequency f and decay time τ for Pt/Co/Pt films were evaluated from thetime-resolved data by fitting the damped harmonic function, and then the experimental
data of f and 1/τ were analyzed by using Landau-Lifshitz-Gilbert equation, a basic
equation of motion of magnetization:dmdm.
= − γm × H eff + αm ×
dt
dt

(1)

Here, m, γ, H eff , and α are the unit vector of magnetization direction, the gyromagnetic
ratio, the effective magnetic field, and the dimensionless damping constant. Extracted
damping constant α increases, up to 0.4, with decreasing Co layer thickness, thosevalues are by a factor of 10-100 larger than those in the ordinary magnetic materials,
such as iron. This means that huge electric power needs to control magnetization
direction of Co layer in these films.
6. Ultrafast precessional spin dynamics in Mn-Ga alloys
As mentioned earlier, some types of magnetic materials naturally forms atomicallylayered structure that leads to tetragonal distortion of crystal lattice, or some types ofmagnetic materials have hexagonal lattice. These crystal structures have an axial
symmetry, leading a uniaxial magnetic anisotropy along c-axis. In case that those films
are textured along c-axis, perpendicular magnetic anisotropy appears. A hexagonal
CoCrPt and tetragonal FePt alloys are, respectively, the materials used in the storage
media currently and possibly near future, so that we investigated magnetization57

Mn atom(b)

Magnetization(emu/cc)
M (emu/cc)

(a)

500

0

H⊥filmH // film-500

Ga atom

-20

-10

0

10

20

Magnetization(emu/cc)
M (emu/cc)

H (kOe)Magnetic
field (kOe)H⊥film500

H⊥film0

H // film

-500
-20

Mne atom

-10

0

10

20

H (kOe)Magnetic field (kOe)

Figure 4. (a) Schematic illustration of crystal structure of L10-MnGa and D022-Mn3Ga.
(b) Typical hysteresis curves for the films having L10 or D022 crystal structures.

dynamics in those materials [16-18]. Here, we show only the recent result of Mn-Ga
alloy films [19].
A Mn-Ga binary alloy has a tetragonal crystal structure and large uniaxial anisotropy[Fig. 1(a)], that is similar to that for a FePt alloy. This material contains no noble andrare-earth metals which are important constituents to gain high magnetic anisotropy,
such as FePt or Nd 2 Fe 14 B. Curie temperature for Mn-Ga alloys is much higher thanroom temperature, and the large spin polarization has also been predicted in Mn3 Ga[20], nevertheless those contain no magnetic elements, i.e., Fe, Co, and Ni. We
succeeded, for the first time, to grow Mn2.5 Ga epitaxial film using ultra-high vacuum
magnetron sputtering technique and reported a huge uniaxial perpendicular magnetic
anisotropy constant over 10 Merg/cc with low saturation magnetization ~ 250 emu/cm3[21]. High-TMR ratio has also been predicted by our group [22]. However, there aremany open questions, especially magnetic damping constant.
Figure 4(b) shows the typical hysteresis loops for the Mn-Ga films with different
composition with applying field of out-of-plane (in-plane) denoted by red (blue) curves.
Both films show good perpendicular uniaxial anisotropy and very large effective
anisotropy field H k eff, close to 10 T, was estimated from the hysteresis loops. Figure5(a) shows the typical time-resolved magneto-optical Kerr signals for the films.
Sinusoidal oscillations correspond to magnetization (spins) precessions about an58

f (GHz)

300

-10
-20
-30

250
exp.

200

(c)

0.12 (mJ/cm2)
-40

0.02

0.28
0.43

-50

0.83
-60
0

(b)

Laser intensity

αeffsignal (arb. unit) (arb. unit)
Kerr signalKerrintensity

0

20

40

0.01

(a)
60

0
30

80

Delay time (ps)

40

50

60

70

80

90

θH (°)

Delay time (ps)Figure 5 (a) Typical example of time-resolved magneto-optical Kerr effect of the MnGa film with L10 structure. Magnetic field direction θH dependence of (b) precession
frequency and (c) effective damping constant for L10 and D022 Mn-Ga films.

externally applied magnetic field. Spin precessions show ultrafast frequencies over 100
GHz with no remarkable decays, that have never been observed in metallic
ferromagnets, so far.
Precession frequency f are extracted from the data are shown in Fig. 5(b) as afunction of magnetic field direction. Experimental data of f are well fitted to the data
calculated from eq. (1) with adequate fitting parameters. The damping constants α are
also extracted from the data [Fig. 5(c)], average values of 0.015 and 0.0075,
respectively, for L1 0 and and D0 22 Mn-Ga alloys. First-principles calculations are alsoin qualitative agreement with these experimental results [19].
4. Discussion
The damping constants for various films with perpendicular magnwetic anisotropy
are plloted as a function of the perpendicular anisotropy constant in Fig. 6. The reported
materials with large perpendicular magnetic anisotropy show large damping constants
as shown in Fig. 6. However, damping constants for Mn-Ga alloys are by a factor of ten
smaller than known materials even though this materials have a large perpendicularmagnetic anisotropy. As we mentioned earlier, the origin of both perpendicularmagnetic anisotropy and magnetic damping relate to quantum mechanical spin-orbit
interaction from the theoretical points of view [8,9]. Thus, the compatibility of small
damping and large perpendicular magnetic anisotopry in Mn-Ga alloys is not only59Magnetic damoping
α coefficient α

Reported
Values invariousmaterials

10-1

10-2
Requiredvalues for
Gbit-STTMRAM

10-3
10-1

100

101

Perpendicular magnetic anisotropy
constant Kueff (Merg/cm3)
Figure 6 Magnetic damping constant α as a function of effective uniaxial perpendicularmagnetic anisotropy constant Kueff for various types of perpendicular magnetization
films.

technologically but also fundamentally interesting. One reason of small damping is that
this alloy has small density of states at Fermi level and no constituent of heavy elements[19,23]. Full understanding needs further investigations.
4. Summary and prospect
We have achieved the construction of set-up, the investigation of dynamics forvarious magnetic films with perpendicular magnetic anisotropy, and the discovery of
excellent properties in Mn-Ga alloys. This finding contributes not only to develop STTMRAM but also to form the new concept for designing Green Spintronics Materials
with no heavy elements. The Mn-Ga alloys has potentially high spin polarization andexhibit high-TMR ratio, so that it is important to investigate spin transport properties of
MTJ with Mn-Ga, such studies are in progress [24].
It is important to continue to explore materials with much better properties for STTMRAM. Such new materials could be created by controlling atomic layer structure
including light element as well as electronic structure around Fermi energy.
It is naturally considered that a high speed motion of spins, demonstrated in our
optical experiments in the Mn-Ga films, can be applied to a high speed spintronics
device. Such a new devices should be useful for nonvolatile logic application, that is60

one of the future directions of research.
Acknowledgements
We sincerely thank our colleagues; F. Wu, E. P. Sajitha, D. Watanabe, T. Kubota, X.
Zhang, Q. Ma, M. Araidai, and Prof. M. Tsukada (WPI-AIMR), H. Naganuma, M.
Oogane, and Prof. Y. Ando, and Prof. A. Sakuma (Department of Applied Physics), Y.
Miura and M. Shirai (RIEC), and J. Walowski (Goettingen University). These studies
were partially supported by NEDO Spintronics Nonvolatile Devices Project, Grant-inAid for Scientific Research from JSPS and MEXT, Grant for Industrial Technology
Research from NEDO, FIRST Program from JSPS, Strategic International Cooperative
Program “ASPIMATT” from JST, and Asahi glass foundation.
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GI3 VISITING PROFESSOR LIST
Term

Name

Affiliation

Position

Host PI

Daniel Miracle

AF Research Laboratory

Senior Scientist

Louzguine

2011/8/14-

2011/9/24

Richard Tilley

Victoria University of Wellington

Associate Professor

Ajiri

2012/3/16-

2012/4/16

Zhang Di

Shanghai Jiao Tong University

ProfessorChen

2012/2/3-

2012/3/2

GI3 VISITING SCIENTIST LIST
Term

Name

Affiliation

Home PI

Host PI

Jorg Fromel

Fraunhofer Institute ENAS

Gessner

Esashi2011/5/11-

2011/11/30

Weichin Lin

University of Cambridge

Gessner

Esashi2011/12/15-

2012/3/31

Yu Lang Chu

Chemnitz University of Technology

Gessner

Esashi2012/2/15-

2012/9/30

Jia Chenping

Fraunhofer Institute ENAS

Gessner

Esashi2012/3/8-

2012/6/29

Yaofeng Guo

Institut Polytechnique de Grenoble

YavariLouzguine

2012/2/15-

2012/4/15

Olga Ivanova

Institut Polytechnique de Grenoble

YavariLouzguine

2012/2/15-

2012/4/15

63