CRN Science
& Technology Essays - 2008
"Four
stages of acceptance: 1) this is worthless nonsense; 2) this is an interesting,
but perverse, point of view; 3) this is true, but quite unimportant; 4) I always
said so."
— Geneticist J.B.S. Haldane,
on the stages scientific theory goes through
Each issue of the
C-R-Newsletter
features a brief article explaining various aspects of advanced
nanotechnology. They are gathered in these archives for your review. If you have comments
or questions, please
email
Jessica Margolin, CRN's Director of Research Communities.
1.
CRN at Five Years Old (January 31,
2008)
2.
Atomic Force
Microscopy (March 31, 2008)
2004 Essays Archive
2005 Essays Archive
2006 Essays Archive
2007 Essays Archive
CRN at Five Years Old
By Mike
Treder, Executive Director
In December
2007, we stated that this month we would offer an assessment of CRN’s first
five years and present an overview of our accomplishments, our disappointments,
and our plans for the future.
A useful way to
approach this task might be to go back and consider what we believed and what we
said when we started CRN and what we have learned since then.
Early in 2003, we published the following
foundational statements that summarized CRN's basic
positions:
A) Effective use of nanotechnology can
benefit everyone.
Advanced nanotechnology promises the
ability to build precise machines and components of molecular size. Using
mechanically guided chemistry, rapid prototyping, and automated assembly, a
nanofactory could combine components into large and complex products. A
personal nanofactory should be able to provide cheap, clean, rapid
manufacturing; the resulting abundance has the potential to alleviate most
shortages, and enable a high standard of living for everyone who has access to
it. Rapid, cheap, flexible manufacturing will allow swift development of new
inventions, spurring innovation and creating further benefits. We are
dedicated to the principle of making these benefits available as widely as
possible through effective administration of molecular manufacturing.
B) Unwise use of nanotechnology can be
very dangerous.
A technology this powerful could easily be
misused. The rapid development cycle and massive manufacturing capability may
lead to an unstable arms race between competing powers. Excessive restrictions
may lead to an inhumane gap between rich and poor, and may encourage a black
market in bootleg, unsafe molecular manufacturing technology. Insufficient
restrictions may allow small groups and even individuals to produce
undesirable products or terrorist tools. The products of a nanofactory could
have unprecedented power and efficiency. Some restrictions, implemented
worldwide, will probably be necessary for sufficient control of the use of
molecular manufacturing.
C) Nanofactory technology can be used
safely.
The manufacturing capability of advanced
nanotechnology might be encapsulated in a device of convenient size, with
built-in mechanisms for restricting the products it can make. A box the size
of a microwave oven would provide ample manufacturing capacity for a
household; such a format would be suitable for private ownership, and is
easily large enough to contain all necessary functionality for safe use,
including elimination of any chemical emissions, and various security
technologies. The security features would ensure that the factory would only
make approved products; several approval processes could be instituted for the
use of various groups and situations. By using nanofactories with built-in
restrictions, necessary control could be imposed while allowing widespread use
of molecular manufacturing.
D) Preventing nanotechnology is
impossible; careful study will be necessary for wise use.
Many nations around the world have already
established nanotechnology programs, spending hundreds of millions of dollars
per year. Many enabling technologies are developing rapidly. There is no
realistic way to relinquish or prevent all development that could lead to
robust molecular manufacturing, and there are compelling military and economic
reasons for its development—in many different countries. Meanwhile, estimates
of the technology's ultimate potential, and the timeline and cost for
development, vary widely. Information is power; only through intensive studies
can we ensure that the developers and the future administrators of this
powerful capability have the tools they need to make the right decisions. A
detailed understanding of molecular manufacturing technology is necessary to
prepare for its eventual development.
E) Effective use of nanotechnology will
require intelligent and prudent policy-making.
Like a computer, a nanotechnology
manufacturing system could be incredibly flexible—useful for a wide range of
tasks. The administration of a single technology with a multitude of uses,
many of them dangerous, poses a unique problem. No single organization can
effectively tackle this problem. A single point of control will not be
responsive enough to choose the correct set of restrictions for every case,
when decisions must be made rapidly and too much restriction may be as bad as
too little; however, some worldwide control will probably be necessary. An
organization with a single focus, such as military or commercial, cannot make
good decisions about unrelated purposes; an organization that tries to
accommodate everyone will probably make unwise compromises. Predicting the
effects of any choice will require a detailed understanding of the potential
of the technology. Well-informed policy must be set, and administrative
institutions carefully designed and established, before molecular
manufacturing is developed.
F) The situation is urgent; nanofactories
may be developed within a decade.
Development of molecular manufacturing
technology will rapidly become easier. Computer chips have parts only 120
atoms wide, and getting smaller; molecules bigger than that have already been
constructed. Several technologies allow direct creation of complex structures
less than 20 atoms wide, and single-atom lithography is being developed.
Automated assembly has been used for decades; rapid prototyping is quickly
developing from industrial to home use. Molecular manufacturing and assembly
will be simpler and easier in many ways than normal manufacturing. Rapid
development programs, some of which may be secret, competitive, and
unregulated, will be driven by powerful economic and military incentives.
To be prepared for the coming development of molecular manufacturing
technology, we must start planning for it immediately.
Let’s take those points one at a time and
see if they still apply today, in early 2008.
Effective use of nanotechnology can
benefit everyone.
— What’s suggested here is that the
benefits of molecular manufacturing might not be
distributed equitably unless we make certain choices. We still believe this, and
although we have offered arguments to support our
position and
engaged others in discussion, the issue is still open and may not be decided
for quite some time. It’s really an old, classic debate about how much the state
should intervene in markets, but we think the unprecedented potential
productivity of advanced nanotechnology makes it more
relevant than ever. We will continue to emphasize this aspect of our message.
Unwise use of nanotechnology can be
very dangerous.
— Over the years, perhaps not surprisingly,
this point has brought more attention to CRN than any other. We have raised
concerns about the potential for a new arms race, about environmental
implications, about job loss and economic disruption, about ubiquitous intrusive
surveillance, and many other dangers. We’re gratified
that the
public at large seems to have caught on to the seriousness of the risks
we’ve raised and placed them in proper perspective versus the still important
but less critical worries about things like nanoparticle toxicity. Of course,
there is nothing close to agreement on CRN’s assertion that “some
restrictions, implemented worldwide, will
probably be necessary for sufficient control of the use of molecular
manufacturing.” That’s one of our most controversial positions, but we have not
yet seen a reason to change it.
Nanofactory technology can be used
safely.
— We’re proud to have taken the lead in
proposing extensive plans for safe use of personal
nanofactories. Our suggested approach of wide distribution combined with
built-in technical restrictions almost always garners positive response.
Granted, it will be anything but easy to design and implement such a system, but
the basic concepts seem to be sound.
Preventing nanotechnology is
impossible; careful study will be necessary for wise use.
— This point was made against a backdrop of
some individuals and groups calling for a moratorium
on nanotechnology research and development or even outright
relinquishment of the technology. Fortunately, such cries have found little
sympathy.
CRN’s position that advanced nanotechnology should be developed as fast as
it can be done safely and responsibly appears to be the mainstream consensus,
and with good reason. The potential benefits are far
too great to be relinquished, and the best way to head off
risks is to carefully study and understand the
technology, and then to develop it under sensible guidelines.
Effective use of nanotechnology will
require intelligent and prudent policy-making.
— There are three key points in this
position: first, that the issues involved are complex and overlapping, meaning
that no simple solution will work; second, that a
laissez faire approach could be very dicey because the
dangers are too great to allow for unregulated dissemination of nanofactory
technology; and, third, that policy choices must be made and
administrative systems put in place before
the technology is complete. The first point seems self-evident and has largely
been accepted, although we suspect that the enormous implications of this
overwhelming complexity are not yet fully appreciated. The second point is
controversial, of course, and this is an area where CRN is open to considering
that we might be wrong. Good arguments can be made for the effectiveness
— indeed, perhaps even the necessity
— of supporting emergent networked
solutions instead of top-down imposed solutions. That’s an ongoing discussion.
The third point is equally controversial, and arguably unachievable, but because
it focuses attention on how molecular manufacturing is potentially so
disruptive, we think it is worth bringing up again and again.
The situation is urgent;
nanofactories may be developed within a decade.
— Now, we get to the heart of the matter.
Unless CRN can establish the urgency factor suggested by this final point, then
all of the other positions stated above may be considered only of academic
interest and not necessary for critical debate, or at least not for a long time.
So, where are we today?
Since CRN was founded in December 2002,
we’ve seen remarkable progress in the development of technologies that may
contribute to the eventual achievement of exponential general-purpose molecular
manufacturing. We won’t go down the whole list, because it is too long (see this
Enabling Nanotech Update for some examples), but it now seems obvious to
us and to many scientists and other observers that the feasibility question is
well on its way to being settled. The contention that building productive
nanoscale machinery is impossible for this reason or that reason has faded into
the background. On the point of whether or not molecular manufacturing is
feasible, CRN and our allies apparently have won the argument.
A larger question exists, however, about
urgency. Feasibility is only one factor; the other is imminence. There is a huge
difference between saying that nanofactories will be developed someday
and saying that they will be developed soon. We have based our appeals to
policy makers and to the public on the idea that immediate
action was needed. Originally, we claimed that the technology “might become
a reality by 2010, likely will by 2015, and almost certainly will by 2020.”
Recently
we revised that projection to say “might become a reality by 2010 to 2015,
more plausibly will by 2015 to 2020, and almost certainly will by 2020 to 2025.”
It’s interesting to note that while CRN’s
time frame for the expected development of molecular
manufacturing has shifted back by approximately five years, the mainstream
scientific community’s position has been moving forward, from a point of
‘never’, to ‘maybe by the end of the
century’, to ‘not
until at least 2050’, and now to ‘perhaps around 2030 or so’. These projections
might not yet match up exactly with CRN’s, but the gap is steadily shrinking.
So, we’re seeing
agreement about feasibility, and a convergence around the likely time frame.
These are both positive developments, as uncertainty is being removed.
And that’s where we stand today. The
Center for Responsible Nanotechnology has accomplished a great deal in five
years, clarifying and sharpening the discussion, forcing our concerns onto the
agenda, and moving the mainstream closer to our positions. Our challenge now is
to take a step back and see what we most want to achieve during the next five
years.
Atomic Force Microscopy
By Michael Berger, editor-in-chief of Nanowerk
(This article was
originally published on March 10, 2008, at Nanowerk.com and is reprinted
here by permission.)
Whenever you read an article about nano this or nano that, chances are you come
across a large number of confusing three-letter acronyms - AFM, SFM, SEM, TEM,
SPM, FIB, CNT and so on. It seems scientists earn extra kudos when they come up
with a new three-letter combination. One of the most important acronyms in
nanotechnology is AFM - Atomic Force Microscopy. This instrument has become the
most widely used tool for imaging, measuring and manipulating matter at the
nanoscale and in turn has inspired a variety of other scanning probe techniques.
Originally the AFM was used to image the topography of surfaces, but by
modifying the tip it is possible to measure other quantities (for example,
electric and magnetic properties, chemical potentials, friction and so on), and
also to perform various types of spectroscopy and analysis. Today we take a look
at one of the instruments that has it all made possible. So far, over 20,000 AFM-related
papers have been published; over 500 patents were issued related to various
forms of scanning probe microscopes (SPM); several dozen companies are involved
in manufacturing SPM and related instruments, with an annual worldwide turnover
of $250–300 million, and approx. 10,000 commercial systems sold (not counting a
significant number of
home-built systems).
To put the AFM in its context: The reason why nanosciences and nanotechnologies
have taken off with such amazing force over the past 20 years is because our
ongoing quest for miniaturization has resulted in tools such as the AFM
(invented in 1986) or its precursor, the scanning tunneling microscope (STM;
invented in 1982. IBM has a website with a gallery of STM images
here).
Combined with refined processes such as electron beam lithography, this allowed
scientists to deliberately manipulate and manufacture nanostructures, something
that wasn't possible before.
These engineered nanomaterials, either by way of a top-down approach (a bulk
material is reduced in size to nanoscale particles) or a bottom-up approach
(larger structures are built or grown atom by atom or molecule by molecule), go
beyond just a further step in miniaturization. They have broken a physical
barrier beyond, or rather: below, which the standard laws of physics are
replaced by what is called "quantum effects". Any material reduced to the
nanoscale can suddenly show very different properties than to what it shows on a
macro- and larger scale. For instance, opaque substances become transparent
(copper); inert materials become catalysts (platinum); stable materials turn
combustible (aluminum); solids turn into liquids at room temperature (gold);
insulators become conductors (silicon).
A second important aspect of the nanoscale is that the smaller nanoparticles get
the larger their relative surface area becomes. The larger the relative surface
area, the more reactive a particle becomes with regard to other substances. The
fascination with nanotechnology stems from these unique quantum and surface
phenomena that matter exhibits at the nanoscale, enabling novel applications and
interesting materials.
But without the AFM, all this wouldn't be happening.
The term microscope in the name is actually a misnomer because it implies
looking, while in fact the information is gathered by feeling the surface with a
mechanical probe. The operation principle of an AFM is based on three key
elements:
1) an atomically sharp tip (the "probe"), placed at the end of a flexible
cantilever beam, that is brought into physical contact with the surface of a
sample. The cantilever beam deflects in proportion to the force of interaction;
2) a piezoelectric transducer to facilitate positioning and scanning the probe
in three dimensions over the sample with very precise movements; and
3) a feedback system to detect the interaction of the probe with the sample.
Scanning across the surface, the sharp tip follows the bumps and grooves formed
by the atoms on the surface. By monitoring the deflections of the flexible
cantilever beam one can generate a topography of the surface.
This principle has been the basis for one of the most important nanoscience
tools and allowed the visualization of nanoscale objects where conventional
optics cannot resolve them due to the wave nature of light.
A recently published article in the Encyclopedia of Life Sciences,
written by Martijn de Jager and John van Noort, both from the University of
Leiden in the Netherlands, gives an excellent overview of
Atomic Force Microscopy
and its applications in life sciences. Below we are summarizing some of the key
information from this article.
The AFM can be operated in a number of modes, depending on the application but
four modes are most commonly used for AFM imaging: contact mode (or constant
height mode), where the deflection of the cantilever is directly used as a
measure for the height of the tip and the normal force applied to the sample
scales directly with its height. In constant force mode, the normal force the
cantilever deflection under scanning reflects repulsive forces acting upon the
tip, and at sufficiently small scanning velocities the force feedback can reduce
the normal force. Tapping mode (or noncontact mode), where the tip is vibrated
(oscillating at its resonance frequency) perpendicular to the specimen plane to
avoid gouging the specimen as the tip is scanned laterally and the lateral
forces are reduced. In a fourth mode of scanning, the force–distance mode, the
tip is brought to the sample at frequencies far below the resonance frequency of
the cantilever while at the same time the deflection is recorded. This allows
one to measure the local interaction as a function of the tip-sample distance.
As de Jager and van Noort write in their article, large numbers of various
biological samples, including cells, cell compartments and biomolecules, have
been studied with AFM. "In some of these studies, AFM is used as a plain imaging
tool to investigate the topography of immobilized and/or fixed samples,
complementing existing methods such as electron microscopy, with the advantage
that sample preparation is generally more straightforward. For other
experiments, the use of AFM is a prerequisite to look at nonfixed materials and
even their dynamics in aqueous environment. Besides its imaging capabilities AFM
is becoming increasingly important as a nanomanipulation tool. The
single-molecule analysis of interaction forces, elasticity and tertiary protein
structure in intact biological materials is uniquely possible using AFM."
Introducing this vast body of research is beyond the scope of any article. Let's
just take a look at two examples illustrated in the paper:
Imaging Cells
"AFM imaging of living cells provides a direct measurement of cell morphology
with nanometer resolution in three dimensions. Because of its noninvasive nature
and the absence of fixation and staining, even dynamic processes like exocytosis,
infection by virus particles and budding of enveloped viruses have been
successfully visualized in successive scans. Owing to the high elasticity of the
cell membrane, the tip can deeply indent the cell without disrupting the
membrane. Making use of this effect, even submembraneous structures such as
cytoskeletal elements or organelles like transport vesicles can be revealed.
However, due to the elasticity of the cell the contact area between the tip and
the sample increases with increasing applied force. The elastic modulus of
living cells varies between 10 and 100 kPa, which results in a tip sample
contact area of 50–100nm in the softest region of the cell. Therefore, the
(sub-) nanometer resolution that is routinely achieved on more rigid samples
cannot be achieved on membranes of intact cells."
Structure, Function and Interaction of Single DNA and Protein Molecules
"Besides the analysis of cells and cell membranes, AFM-based methods to study
purified single molecules like proteins, deoxyribonucleic acid (DNA) and
ribonucleic acid (RNA) have developed rapidly in the past decade. Unique details
on the mechanism and function of DNA- and RNA metabolizing proteins can directly
be obtained by quantification of the number, position, volume and shape of
protein molecules on their substrate. Like other single molecule techniques all
individual instances of the entire population of structures are revealed, also
showing rare but important species. Further insights in the mechanism of a
reaction can be obtained from image analysis by measuring parameters such as
protein-induced DNA bending, wrapping and looping. Besides topography imaging,
force spectroscopy has been successful in unraveling tertiary structure in
proteins, RNA and other polymers."
Although it already is an essential tool for structural analysis and
manipulation of complex macromolecules and living cells, it is to be expected
that AFM-based applications will be further extended in the future. Technical
developments will advance the AFM system itself, by improvement of resolution,
image rate, sensitivity and functionality. A combination with complementary
techniques will fill in some limitations of AFM.
To fully exploit the potential of AFM to study functional biomolecules and their
interactions, de Jager and van Noort say that video microscopy would be needed
to capture dynamic events. "Currently, the scan rate is limited by the
mechanical response of the cantilever and the piezo. Smaller cantilevers will
result in higher resonance frequencies, allowing faster scanning rates. By
reducing the size of the cantilevers one order of magnitude, the frame rate can
be reduced from typically a minute down to video rate, allowing the study of a
significantly larger range of biomolecular processes."
The two researchers expect the most important developments for the tip itself.
"Image resolution in all modes is dependent on tip geometry. The reduction of
tip size, increase of its aspect ratio and its resistance to wear as a result of
scanning will have a considerable impact on all AFM applications."
For instance, researchers at Harvard and Stanford universities have developed a
specially designed
AFM
cantilever tip, the torsional harmonic cantilever (THC), which offers orders
of magnitude improvements in temporal resolution, spatial resolution,
indentation and mechanical loading compared to conventional tools.
With high operating speed, increased force sensitivity and excellent lateral
resolution, this tool facilitates practical mapping of nanomechanical
properties.
