Technology and the future of medicine

The promise and perils of nanotechnology

Michael T. WoodsideNational 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 withnanotechnology

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 uncertaintieshttp://www.nanotec.org.uk/finalReport.htm

Drexler-Merkle differential gear(model), 1995

Richard Feynman: “There’s plenty of room at the bottom”

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.

Address to American Physical Society, 1959:

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 scaleThe marvelous biological systemProblems of lubrication and waste heatRearranging atoms…

Popularisation: Eric Drexler

Influenced by ideas of “limits to growth” in afinite world

Controversial reception inscientific community

Drexler-Smalley debates2001-2003

Inspired by Feynman, molecular biology

Impact on public perception1986

Nanotechnology: PromiseMany possibilities have been conceived:

• New materials with enhanced properties: strength, durability, functionality,…

carbon nanotube space elevatorcoloured nanoparticles

invisibility cloak

diamandoid

Quantum computers

Nanotechnology: Promise

Combination with AI:swarm of intelligent

computation

Assemblers

Assemble anything fromatomic constituentsUse “quantum wierdness”

to solve intractable problems

Smartdust

wirelessly networkednanosensors

Many possibilities have been conceived:

“molecular nanotechnology”

Also energy storage, transmission, ...

• Drug delivery

Nanotechnology: Promise

Medical “nanobots”

• Distributed sensing and real-time monitoring

• Interface with neurons: expandmental capabilities

• Enhanced physical capabilities: strength,endurance, …

Many possibilities have been conceived:

• Enhanced immune system

• Cellular repair

• Longevity

Combine with AI and synthetic biology

• Cure diseases in real-time

1. Biology provides proof of the feasibility of nanotechnology, supplies a fully functional model

5. Structures where atoms are arranged precisely exist in Nature

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

The motivation for molecular nanotechnology

Hence we should be able to build nanoscale, self-replicating, programmable “assemblers” capable of manufacturing

arbitrary objects from atomic constituents

Molecular nanotechnology:

“Thorough, inexpensive control of the structure of matter based on molecule-by-molecule control of products and byproducts of molecular manufacturing.”

The basic concept

Based on:

The concept of the molecular “assembler”: pick up and manipulateatoms, establish chemical bonds between arbitrary atoms

Incorporation of assemblers into self-replicating machines

Molecular-scale computation, programming, data storage,and integration

Unbounding the Future, Drexler et al., 1991

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

…but many potential dangers lurk!

www.zyvexlabs.com/Publications2010/WhitePapers/MolecularNanotech.html

Nanotechnology: Perils

Again, many possibilities have been conceived:

Tiny, invisible weapons

New toxic materials,easily spread and hardto contain

Self-replicating weapons

Weapons control impossible:hard to embargo, hard to verify

competition from ETC group

“GI Joe” (2009)

Undetectable and pervasive surveillance: totalitarian nightmare

Medical nanobots: remotecontrol of health

Neural interfaces:thought control/possession

Nanotechnology: Perils

More insidious dangers:

Consequences of system crashes in enhanced bodies and minds

Change in the economic basis of society

Societal fragility: consequences of network crashes in complex systems run by pervasive smartdust mesh

Emergent complexity

Swarm intelligence

Nanotechnology: Perils

Higher-level dangers:

2002 2000

Self-replication of assemblers, “grey goo”

Nanotechnology: Perils

Ultimate nightmare scenarios:

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-basedelectronics!

But: 15 years on, still can’t grow them to order—so how can they form thebasis 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 CNTsto order…

…circuits would be 10,000-1,000,000 denser!

• How do we connect to theoutside (“macro”) world?

• How do we check that it’sbuilt properly?

Practical problems that are “justengineering”… but are very hard and have no obvious solution!

(Un)Fortunately reality intrudes…

More basically: flawed philosophical premise for molecular nanotechnology

NOAnd it never has been!

Is it even possible to build today anything that we canconceive, provided it does not violate physical laws?

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

• Fluctuations become relatively more important as size decreases

• Quantum phenomena become inescapable at atomic scales: wave/particle duality, tunneling, probabilistic vs deterministicbehaviour,…

• 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?

Issues ranging from the mundane to the fundamental:

• Heat dissipation: as physical size decreases and density of componentsincreases, waste heat becomes a problem just as in computers today

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 systemsknown:

DNA polymerase: reliablereplication, with error rate

~ 1 in 10,000,000,000

F1F0 ATP synthase: mostefficient motor known

(~90-100%)

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)

How do we design, de novo, both novel chemistries or functions, and the folds protein folds to achieve them?

Biology as a template

But we still can’t reliably predict folding for known structures after decades of intensive research!

Yet another fundamental roadblock: heterogeneity

How can one manufacture complex assemblies efficiently and reliablywithout uniform, quality parts?

As in regular manufacturing, heterogeneity inhibits complexity—needstandardised, interchangeable parts

One can’t!

Complex processes with multiple steps: need reliable yield above all

1 step: 97% correct yield20 steps: 50% worthless junk!

Self-assembly is statistical, not deterministic: will always yield mixturesand distributions of products

Comparisons of heterogeneity

ii iShannon ppH 2log lnBBoltzmann kS

Boltzmann entropy (disorder): Shannon entropy (information):

Define generalised negentropy: ,...,,ln precisionpurityerrorS

polymerdispersion

nanoparticlesize dispersion

0 5 10 302015 25

human typing

transcription

Taq polymeraseoptimised PCR

DNA replication

precisionmachining

booktypesetting

telescopemirror

crystal purity

digitalcomputing(> 50)

integratedcircuit components

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