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 Bernie Yurke Bernie Yurke has a PhD in Physics from Cornell University, and a BS and an MA, both in Physics from the University of Texas at Austin. He started working at Bell Labs in 1982. He has performed research in the areas: force generation of microtubules, phase-ordering kinetics in liquid crystals, and squeezed state generation at optical and microwave frequencies. His current research focuses on self-assembly using DNA. Bernie was awarded the 2001 Max Born Award and is a Fellow of the American Physical Society, the Optical Society of America, and the American Association for the Advancement of Science. He is a member of the Biophysical Society. One of his hobbies is paleontology. Yurke and his colleagues have created DNA �motors� - chemically operated devices 100,000 times smaller than the head of a pin. And in the growing field of nanotechnology, the manipulation of atoms and molecules, the idea of using DNA is viewed quite favorably. DNA stores huge amounts of information. Nanotechnologists like Yurke and his team say that DNA is nature's way of storing huge amounts of information in a tiny space. The space between each symbol in the genetic code is 0.34 nanometer (one billionth of a meter). Existing electronics technology makes features about 100 nanometers in size - more than 100 times bulkier than what DNA would provide. Making a DNA-based computer would be another story. The DNA motors created by Yurke and his colleagues are so small that they don't show up on optical microscopes. So the researchers must rely on fluorescence. Dye molecules are attached to the ends of the DNA strands and a laser is used to "excite" the dyes. Yurke says the closing and opening of the V-ends of the DNA motor (also called a "tweezer" because of its V shape) are measured by the amount of light being given off - noting that more light means the V-end is open, and less means it's closed. This interview was conducted by Haym Benaroya and took place between November and December 2001.
Bell Labs' Bernard Yurke (far right) and his
colleagues (left to right) Allen P. Mills, Jr., Rutgers graduate student
Jennifer Neumann and Friedrich C. Simmel. The team created chemically
operated DNA "motors." Resonance:
Nanoscience
and technology are very exciting fields of research today. Also, major
advances are being made in nanobiology with one goal being the utilization
of nature�s building blocks for technological needs of people and
society. Can you please summarize the essential aspects of your work, and
then, what applications you have in mind that you are working toward? Yurke:
Information
technologies have benefited tremendously by our ability to manufacture
things on an ever-smaller scale. The
continued shrinking of the transistor has made possible an exponential
growth of computing power in personal computers, a trend that has lasted a
quarter of a century. There
is reason to believe that this trend will come to an end within a decade
as the technologies used to manufacture these transistors are pushed to
their limits. There is a
search underway for alternative technologies that might allow one to go
beyond these limits. This
drives much of the current work in nanotechnology.
We now know
that single molecules can serve as electronic switches. The challenge now is to figure out how to assemble such
components together into complex information processing circuits.
I am exploring the possibility of using molecules to direct the
self-assembly of such circuits. DNA
is a very convenient material to use in these investigations.
Two strands of DNA will stick together to form a double helix only
if their base sequences are complementary, that is, if each A of one
strand matches a T from another strand and if each C from one strand
matches a G from the other strand. If
there are a sufficient number of base mismatches, two strands of DNA will
not stick together. Thus,
with sufficient care in picking base sequences, sets of DNA strands can be
designed in which two DNA strands from the set will stick together only if
their base sequences are complementary.
Such sets of DNA are said to exhibit �molecular recognition.�
By tagging molecular-scale electronic components with DNA strands,
the DNA can direct the self-assembly of a complex network, in that, two
components will be held next to each other only if they possess DNA
strands whose base sequences are complementary.
Such components when mixed together in a water solution will
diffuse around and self-assemble into the network, the DNA acting as a
kind of smart glue holding together those components that are supposed to
be next to each other. The construction of a DNA-based molecular motor was,
for me, an exercise in learning how to do self-assembly using molecular
recognition. Three strands of
DNA were designed so that when mixed together in solution they would
self-assemble into the V-shaped structures we refer to as molecular
tweezers. The motor used to
close and open the tweezers consisted of single strands of DNA extending
from the arms of the tweezers. These
single-stranded extensions could bind with complementary regions on a
strand of DNA we called the fuel strand.
By forming base pairs with these extensions, the fuel strand pulls
the tweezers shut. The
complement of the fuel strand is able to strip the fuel strand from the
tweezers and restore it to its open configuration.
It is the self-assembly aspect of the DNA-based
molecular motor research that is of most relevance to the assembly of
molecular-scale electronic circuits using molecular recognition.
However, knowing how to build molecular motors may come in useful
for molecular-scale assembly as well.
Whatever the assembly process, it will produce errors.
Knowing how to build molecular motors opens up the possibility of
devising molecular machines that could correct these errors. Resonance:
How
far are researchers such as yourself from realizing your goals? Is this a
realistic question? Yurke: A
wide variety of nanoscale structures have been fashioned out of DNA.
Examples include wire frame polyhedra, tubes, sheets, and various
kinds of molecular devices, such as our tweezers.
Nadrian Seeman�s group at NYU did much of this work.
The assembling together of nanometer-sized metallic wires using DNA
has been demonstrated by Tom Mallouk�s group at Penn State.
The assembly of a molecular-scale electronic circuit, using
DNA-based molecular recognition, remains to be demonstrated, but I expect
this to happen within a few years� time.
The big unknown is whether this type of assembly can be scaled up
to assemble networks of sufficient complexity and with sufficient yield to
be of interest to the electronics industry.
The image above shows the tweezers completely closed. Resonance:
One generally does not think of Bell Labs and Lucent as sites of
bio-related research. Beyond the excitement and prestige of supporting
such visionary research, where does Lucent see a payoff to its businesses
from your research? Yurke:
Bell Labs has served the needs of two high technology companies,
first AT&T and then Lucent. A part of this has been the development of tools for the
characterization of materials and for the control of fabrication
processes. The application of
such tools to bio-related problems is one way of pushing their
development. Much of the
bio-related work that has been carried out at Bell Labs, including the
application of nuclear magnetic resonance (NMR) to the investigation of
biological problems and development of magnetic resonance imaging (MRI)
technology, fits into this category.
Bell Labs also serves as a source for new technologies relevant to
the telecommunications industry. Biology
sometimes provides inspiration for the invention of such technologies.
Bell Labs researchers working in neurobiology, for example, devised
neural network learning algorithms that have found application in adaptive
software. My foray into molecular biology was driven by the
expectation that biology might have something useful to tell us about
assembly at the molecular scale. For
me, biology serves as a source of inspiration and as an existence proof
that certain kinds of things can be done even though we may not yet know
how to do them. One of the
trends in electronic information processing technology has been the
exponential decrease of component size.
The recognition of this trend with its implication that in the not
very distant future it may be useful to know how to assemble
nanometer-sized parts into complex structures is one reason why my work
has been supported. Resonance:
Are there many groups in the US working on DNA-based nanotechnology? Yurke:
The
number of groups involved in DNA-based nanotechnology is small but
growing. The ones that
immediately come to the top of my mind are Nadrian Seeman�s group at
NYU, Erik Winfree�s group at Caltech, Tom Mallouk�s group at Penn
State, and Chad Mirkin�s group at Northwestern. Resonance:
What are the major stumbling blocks to progress? Size? Biochemistry? Yurke:
Currently
the major hurdle is chemistry. Water
soluble versions of molecules capable of electronic switching or of
serving as molecular-sized electrical wires will have to be synthesized
and new techniques will have to be devised for attaching these to DNA. Resonance:
In non-bio-nanotechnology, it is my understanding that one of the major
challenges is to model across length and time scales. For example, if I
want to build a rocket out of carbon nano-sheets, it would require that I
understand the large-scale properties of the material as a function of the
nano-scale properties. This knowledge would permit me to design the rocket
structure properties more effectively. This is currently not possible. Is
one of the goals of your research group to evolve DNA nanosystems so that
they have large-scale applications? Then similar issues to those I
described above would be a problem? Yurke:
Issues concerning how well
self-assembly, using molecular recognition, will scale as the complexity
of the structure being assembled increases will have to be addressed.
Bulk materials properties are less of an issue in assembly since
the assembled network is likely to be placed on a rigid support substrate
or it may even be directly assembled on such a substrate. Resonance:
Speaking
to a young person about 13-14 years old, just entering High School, what
advice would you offer? Yurke:
My main advice is to learn as much as you can.
If there is a particular profession that you would like to go into,
try to find someone who works in that profession who can serve as a
mentor. Get involved in
activities relating to that profession. If
you wish to go into a technical field, take as much science and math as
you can. It will also help
tremendously if you pick up a technical hobby that involves building
things, conducting experiments, or making scientific observations. Resonance:
What are
the great-unanswered questions in science today and in the forseeable
future? Yurke:
I see several really big holes in our
understanding of the physical universe.
One is: �What is the universe made out of?� There is good evidence that 90% of the matter
in the universe is not made of any substance that we are familiar with.
This matter is referred to as dark matter because it is not
directly observed through our telescopes.
Its presence is inferred by the apparent existence of gravitational
forces that cannot be accounted for by the
matter we can see.
Determining what this substance is will be a great challenge for
cosmologists and particle physicists.
The other really big hole in our understanding is: �How did life
begin?� We have a very
compelling theory for how life evolves but none of the suggestions for how
it got started in the first place are compelling.
Finding a compelling scenario for how the transition from nonliving
to living took place presents a fascinating challenge. Resonance:
Why are so
few scientists seen in positions of policy authority? Where is their
education going �wrong�? Yurke:
My
guess is that if one compares the fraction of the general population that
are scientists with the fraction of positions in policy authority that are
filled by scientists one will find that scientists are not
underrepresented. However,
with advances in medicine and technology and with the increasing stress
the human population places on natural resources, scientific issues will
be of increasing relevance in making policy decisions.
So, scientists will have increasingly more to offer to this
process. I think the scientific community owes a debt of gratitude to
those who take time from their research to get involved in policy-making
or in educating the public on scientific issues.
Resonance:
You work with graduate students. Do you think that institutions of higher education are
appropriately preparing this nation�s scientists for the future? Yurke:
I believe they are. It is to their own best interest that institutions of higher
education insure that their students are competitive in the job market
once they receive their degree. This
makes them sensitive to the needs of society and industry. Resonance:
Where do
we lose the scientific and mathematical interests of our junior and high
school students? Especially women? Yurke: I see this as more of a societal problem then as a
problem with the educational system. I think the attitudes that parents
hold toward education and towards the roles of women have a lot to do with
this. I think this accounts
for the underrepresentation of children from mainstream America, compared
with first- generation immigrants and children of professional families,
among those who go on to get advanced degrees.
Among the reasons I would suggest for why mainstream America is
relatively infertile ground for the production of scientists and other
professionals are the following: It
is still fairly easy to make a decent living without a higher education,
so a good education is undervalued. Also,
there is an undercurrent of anti-intellectualism in American society, some
of which is a reaction to the challenges that scientific discoveries
present to religious faith. Informing
the public of the benefits it has received through science and
communicating the adventure involved in scientific discovery may help in
changing some of these attitudes. Resonance:
When did you realize that you wanted to study science and physics? Can you
see yourself doing anything other than what you are doing at Lucent? Yurke:
I was always fascinated by the natural world.
Already by the fourth grade I knew that I wanted to be a scientist.
It was molecular biology that peaked my interest in physics.
I was introduced to the world of molecular biology by a book I
checked out from the children�s section of the Boise Public Library
during the summer after I had finished the sixth grade.
It described a world too small to be seen with an optical
microscope, a world where DNA replication, protein synthesis, and the
conversion of food into energy takes place. I wondered how it was possible to deduce what was going on in
such a small world. So, the
next time I visited the library I checked out a college textbook on
molecular biology. The text
was sprinkled with equations from physics and it had a large appendix on
thermodynamics. I began to
see the laws of physics as powerful tools for probing worlds beyond the
direct reach of our ordinary senses and I also began to regard physics as
foundational to all other sciences. From
then on I was hooked on physics. Working
at Bell Laboratories was the fulfillment of a childhood dream.
I regard it a great privilege to work there. I have been given the opportunity to work in those fields in
which I feel I can make the biggest contributions. There is no place where I would rather work.
Resonance:
Can a
degree in physics be viewed as a liberal education? Yurke:
A physics degree is a legitimate degree for a
liberal arts institution to grant. But,
receiving a liberal arts education implies that the education includes a
healthy dose of the many types of intellectual endeavors that human beings
engage in. The study of
physics at the exclusion of coursework in the arts and humanities has too
narrow a focus to count as a liberal education. Resonance:
What is an appropriate educational path for someone who wants to become a
part of the nano-revolution? Yurke:
Most of the activity in nanotechnology is at the
interface between physics, chemistry, and biology.
I would recommend absorbing as much as one can of each of these
fields. The focus in the
physics education should be on condensed matter and its prerequisites:
mechanics, electromagnetism, quantum mechanics, and statistical mechanics.
Within chemistry the emphasis should be on physical chemistry and
organic chemistry. Within
biology the emphasis should be on molecular biology.
Also, one should take a good laboratory course in electronics that
covers instrumentation and measurement techniques.
Resonance:
Is
there a risk that corporations are relying too much on academic research?
Isn�t this a long-term detriment to academic research, which really
should be focused on research that has no obvious or immediate
application? Isn�t this how many of our most important products evolved?
For example, the output of Bell Labs in the 40�s-70�s? Yurke:
I
think that it is fair that those who pay for the research have a major say
in what research gets done. It
is fair for a corporation to ask how the research it funds will contribute
to its bottom line and it is fair for the taxpayer to ask how he or she
will personally benefit by the research that his or her tax dollars go to
support. It is up to us
scientists to make our case for how we think research money should be
spent so that those who pay for it will receive maximum benefit.
Economic impact or the impact on public health should not be the
only measures used to evaluate how research dollars should be spent.
I believe that the discoveries of science have spiritual value and
contribute to the enjoyment of life through the harmony and beauty they
reveal. I think this is
particularly true of space exploration and high-energy physics, where the
medical and economic benefits are likely to be rather minor. But the case has to be made that what we are doing is worth
the cost to those who are paying for it.
The degree to which industry should rely on academic research and
the mix of long-term and short-term research that should be present in
academic institutions is also an issue that many parties have a say in and
where scientists have to express their opinions of what is most
appropriate. Resonance:
What are
the roles of art in society? Does art do something for society that cannot
be done by anything else? Yurke:
The
ability to engage in rational thought is only a tiny aspect of what it
means to be human. There are
deeper aspects to human nature that make it possible for us to function as
social beings. The arts are
able to engage these deeper aspects and bring some of them to conscious
examination. The arts allow
us to explore, for example, what it means to live honorably. Such issues
concerning moral judgment are of paramount importance in structuring a
society but are beyond the realm of science to answer.
Resonance:
How are
art and science intertwined? Does science have a role in art? Yurke:
Both endeavors are searches for truth and
beauty; and much of art and science springs from a common human urge: the
desire to understand the universe and one�s place within it.
Science really is a form of art.
It is a creative activity of the mind that would be impossible
without an imagination. Mathematical
symbols are the brush strokes we use to paint our portraits of the
universe. The aesthetic
qualities we look for in our artwork are simplicity and detail.
We are minimalists employing Occam�s razor.
We strive to capture the entire universe in a single equation.
We are also realists, awed by precision agreement between theory
and experiment. Our craft has
magic qualities, including an uncanny predictive power. Science and art both have the
power to transform the world. The
Copernican revolution, the industrial revolution, Darwinian evolution, and
modern physics have all greatly influenced how we view ourselves, and this
has had a significant effect on the art world.
The images produced by science, such as the earth rising over a
cratered moonscape, and the products of science, such as machinery,
rockets, and nuclear weapons, provide artists with provocative symbols of
the human spirit and of good and evil.
Artists are technicians, skilled at operating their instruments,
and they often quickly adopt new technologies when these will help in
their craft. The fruits of science, such as photography, radio, movies,
television, computers, and the Internet, have provided new media for
artistic expression and have given rise to new art forms. Science, through what it has revealed about the universe and
especially through the technology it has spawned, has had a tremendous
effect on art. Resonance:
And what
about the role of art in science? Yurke:
For
the scientist, art serves as a source of inspiration, occasionally as a
source of metaphor for scientific activity, and sometimes as a conscience
reminding us of our social responsibilities.
But, I think, art has had considerably less influence on the
practice of science than science has had on the practice of art.
Given the diversity of beliefs, cultural practices, and artistic
styles that distinguish various cultures, science exhibits a surprising
uniformity that transcends cultural boundaries and time.
Sure, there is bickering as we sort things out at the edge of the
unknown, but these are small ripples on a deep sea of consensus. Why is
there this uniformity in this cultural activity we call science?
We are listening to Mother Nature and we all hear her sing the same
song. Resonance:
Where are the greatest challenges today to American society? Are you
optimistic with the trends? Yurke:
The
great challenge confronting American society is to remain American.
We have created a society where the individual has been greatly
empowered, and, although there is always room for improvement, it has done
well in dealing with diversity. It
is a society that recognizes the value of a limited government and of the
need to protect the rights of the individual.
It recognizes the importance of the right to voice one�s
opinions. It also recognizes that religion is a personal matter
dictated by one�s own conscience, a matter that government should be
neutral towards. It is my
hope that American society will be able to resist the pressures of special
interests and the temptations that arise during times of national crises
or during economically hard times to back-pedal on some of these ideals.
At the present the trends appear mixed to me. Resonance:
If you
could solve just one of humanity�s problems, which one would it be? Yurke:
Much of the world is currently enjoying a level
of prosperity that is unprecedented in human history. When
I think about the long term, however, an earth depleted of its resources
comes to mind and I wonder if a poor, starving, diseased, and overcrowded
mass of humanity in a dusty, sun-baked world is mankind�s ultimate
destiny. I wish I could do
something to insure the long-term prosperity of humanity.
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![[ Yurke, Mills, Neuman, and Simmel ]](interv1.jpg)
