Technology and the future
of medicine
The promise and perils
of nanotechnology
Michael T. Woodside
National Institute for Nanotechnology
and Department of Physics
Outline
1. Introduction, definitions, background
2. Promise and peril at the level of science fiction and hype/doom
3. Constraints on the vision imposed by scientific realities
4. Specific examples of promising, realistic, near-term
nanotechnology applications:
computation with quantum-dot cellular automata
single-molecule tests for drug discovery
4. Specific examples of realistic, near-term concerns with
nanotechnology
What is “nanotechnology”?
Many possible definitions
“Nanoscience is the study of phenomena and manipulation of
materials at atomic, molecular and macromolecular scales, where
properties differ significantly from those at a larger scale.”
“Nanotechnologies are the design, characterisation,
production and application of structures, devices and systems
by controlling shape and size at nanometre scale.”
Royal Society (2004)
Nanoscience and nanotechnologies:
opportunities and uncertainties
http://www.nanotec.org.uk/finalReport.htm
Drexler-Merkle differential gear
(model), 1995
Richard Feynman: “There’s plenty of room
at the bottom”
Address to American Physical Society, 1959:
I would like to describe a field, in which little has been done, but in which an enormous amount can be done in
principle. This field is not quite the same as the others in that it will not tell us much of fundamental physics (in
the sense of, "What are the strange particles?") but it is more like solid-state physics in the sense that it might
tell us much of great interest about the strange phenomena that occur in complex situations. Furthermore, a
point that is most important is that it would have an enormous number of technical applications. What I want
to talk about is the problem of manipulating and controlling things on a small scale.
I will not now discuss how we are going to do it, but only what is possible in principle – in other words, what is
possible according to the laws of physics. I am not inventing anti-gravity, which is possible someday only if the
laws are not what we think. I am telling you what could be done if the laws are what we think; we are not doing
it simply because we haven't yet gotten around to it.
How do we write small?
Information on a small scale
The marvelous biological system
Problems of lubrication and waste heat
Rearranging atoms
…
Popularisation: Eric Drexler
Inspired by Feynman,
molecular biology
Influenced by ideas of
“limits to growth” in a
finite world
Controversial reception in
scientific community
Drexler-Smalley debates
2001-2003
Impact on public perception
1986
Nanotechnology: Promise
Many possibilities have been conceived:
• New materials with enhanced properties: strength, durability, functionality,…
invisibility cloak
diamandoid
coloured nanoparticles
carbon nanotube space elevator
Nanotechnology: Promise
Many possibilities have been conceived:
Quantum computers
Smartdust
Assemblers
wirelessly networked
nanosensors
Use “quantum wierdness”
to solve intractable
problems
Combination with AI:
swarm of intelligent
computation
Assemble anything from
atomic constituents
“molecular nanotechnology”
Nanotechnology: Promise
Many possibilities have been conceived:
Medical “nanobots”
• Drug delivery
• Distributed sensing and real-time monitoring
• Enhanced physical capabilities: strength,
endurance, …
• Enhanced immune system
• Cure diseases in real-time
• Interface with neurons: expand
mental capabilities
Combine with AI
and synthetic biology
• Cellular repair
• Longevity
The motivation for molecular nanotechnology
1. Biology provides proof of the feasibility of nanotechnology, supplies a
fully functional model
2. Structures that are able to self-replicate exist in Nature
3. Nanoscale machines do not violate any laws of physics, in principle
4. We can conceive of “bottom-up” fabrication, even starting from the
atomic level
5. Structures where atoms are arranged precisely exist in Nature
Hence we should be able to build nanoscale, self-replicating,
programmable “assemblers” capable of manufacturing
arbitrary objects from atomic constituents
The basic concept
Molecular nanotechnology:
“Thorough, inexpensive control of the structure of
matter based on molecule-by-molecule control of
products and byproducts of molecular
manufacturing.”
Unbounding the Future, Drexler et al., 1991
Based on:
The concept of the molecular “assembler”: pick up and manipulate
atoms, establish chemical bonds between arbitrary atoms
Incorporation of assemblers into self-replicating machines
Molecular-scale computation, programming, data storage,
and integration
The Promise of Molecular Nanotechnology
“Imagine a manufacturing technology capable of making trillions of
tiny machines — each the size of a bacteria. Each machine could
contain an onboard device programmed to control a set of molecular
scale tools and manipulators. An individual machine could be
designed to manufacture superior materials, convert solar energy to
electricity, or even, ultimately, enter the body to fight disease and
aging at the cellular and molecular level. Materials hundreds of times
better than today’s best materials, vastly more powerful computers,
precise machinery that doesn’t wear out, and a revolution in clean
manufacturing are but a few of the predicted benefits of applying
these new machines.”
source: Zyvex home page
www.zyvexlabs.com/Publications2010/WhitePapers/MolecularNanotech.html
…but many potential dangers lurk!
Nanotechnology: Perils
Again, many possibilities have been conceived:
New toxic materials,
easily spread and hard
to contain
Tiny, invisible weapons
Self-replicating weapons
Weapons control impossible:
hard to embargo, hard to verify
“GI Joe” (2009)
Nanotechnology: Perils
More insidious dangers:
Undetectable and pervasive
surveillance: totalitarian
nightmare
Neural interfaces:
thought control/possession
Medical nanobots: remote
control of health
Consequences of system crashes in enhanced bodies and minds
Change in the economic basis of society
Nanotechnology: Perils
Higher-level dangers:
Societal fragility: consequences of network
crashes in complex systems run by
pervasive smartdust mesh
Emergent
complexity
2002
Swarm
intelligence
2000
Nanotechnology: Perils
Ultimate nightmare scenarios:
Self-replication of
assemblers, “grey goo”
Self-replicating disassemblers
(Un)Fortunately reality intrudes…
No obvious way forward for many of the dreams
Simple example: carbon nanotubes as ideal electrical nanowire
• 1 nm wide
• up to mm long
• very low electrical
resistance
• can be metal or
semiconductor
Carbon-based
electronics!
But: 15 years on, still can’t grow them to order—so how can they form the
basis of a technology to replace Si (purity of 99.9999999% is routine)?
(Un)Fortunately reality intrudes…
No obvious way forward for many of the dreams
Simple example: carbon nanotubes (CNT) as ideal electrical nanowire
Suppose we could make CNTs
to order…
…circuits would be 10,0001,000,000 denser!
• How do we connect to the
outside (“macro”) world?
• How do we check that it’s
built properly?
Practical problems that are “just
engineering”… but are very hard
and have no obvious solution!
(Un)Fortunately reality intrudes…
More basically: flawed philosophical premise for molecular nanotechnology
Is it even possible to build today anything that we can
conceive, provided it does not violate physical laws?
NO
And it never has been!
Consider dream of human-powered flight:
Leonardo’s ornithopter, 1485
First human-powered flight, 1977
400 years later
The laws of physics must still be respected
Issues ranging from the mundane to the fundamental:
• Heat dissipation: as physical size decreases and density of components
increases, waste heat becomes a problem just as in computers today
• Friction: as parts scale down to near-atomic dimensions, what acts as
a lubricant? How do we control inter-atomic interactions so precisely
that some atoms stick together whereas others slide/move freely?
• Fluctuations become relatively more important as size decreases
• Quantum phenomena become
inescapable at atomic scales:
wave/particle duality, tunneling,
probabilistic vs deterministic
behaviour,…
Many pieces of basic science missing
Atomic-level control over manufacturing is chemistry!
Combinations of
atoms and geometries
are constrained by
properties of elements
and chemical bonding
We cannot make arbitrary
structures and compositions
—even relatively simple
structures can be very hard
to make!
cubane (explosive)
Biology as a template
Biological systems are most effective and efficient manufacturing systems
known:
DNA polymerase: reliable
replication, with error rate
~ 1 in 10,000,000,000
F1F0 ATP synthase: most
efficient motor known
(~90-100%)
Biology as a template
Based on simple processes (e.g. polymerisation)
Create one basic geometry (linear chains)
Rely on self-interactions to generate functional structures
automatically (“self-assembly”, “folding” in biology)
But we still can’t reliably predict folding for known structures
after decades of intensive research!
How do we design, de novo, both novel chemistries or functions,
and the folds protein folds to achieve them?
Yet another fundamental roadblock:
heterogeneity
How can one manufacture complex assemblies efficiently and reliably
without uniform, quality parts?
One can’t!
As in regular manufacturing, heterogeneity inhibits complexity—need
standardised, interchangeable parts
Self-assembly is statistical, not deterministic: will always yield mixtures
and distributions of products
Complex processes with multiple steps: need reliable yield above all
1 step: 97% correct yield
20 steps: 50% worthless junk!
Comparisons of heterogeneity
Boltzmann entropy (disorder):
S Boltzmann
Shannon entropy (information):
 k B ln  
Define generalised negentropy:
H Shannon    i p i log 2  p i 
S   ln  error , purity , precision ,... 
Taq polymerase
optimised PCR
nanoparticle
size dispersion
0
transcription
crystal purity
DNA replication
5
polymer
dispersion
human typing
10
precision
machining
15
book
typesetting
20
telescope
mirror
25
integrated
circuit components
30
digital
computing
(> 50)
Solutions
1. Do it right in the first place
Strong driving force
(thermodynamics)
2. Fix it up later
Error correction mechanism
(kinetics)
3. Ignore it
Fault-tolerant architectures
What is “nanotechnology”?
Encompasses
Current areas of research
Current applications