What Is Self-assembly?

What is Self-Assembly?

We know that the basic principle in self-assembly - in molecular structures - is selective stickiness.

That means if two molecular parts have

complementary shapes and charge patterns i.e. one part has a hollow where the other part has a bump, and one part has a positive charge where the other part has a negative charge, then they will stick together in one particular way. This principle can be used in nanotechnology to assemble what we want. Some scientists believe that self-assembly is an important part of nanotechnology, but the technology for it hasn't arrived yet - despite the fact that we can see that process happening everywhere in nature. Positional control plus appropriate molecular tools should let us build a truly staggering range of molecular structures, however it is too costly. When

it

is

manufacturing

possible device

to

design

able

to

a

general

make

purpose

copies

of

programmable

itself,

then

the

manufacturing costs for both the devices and anything they make will be low.

A device like this one has been named by Drexler as Assembler.

In 1940 Von Neumann produced the first analysis related to selfreplicating systems. The architecture for Drexler's assembler is a specialization of the more general design proposed by von Neumann.

Other examples of self-replicating systems such as Internet Worm, Mycoplasma genitalia, human genes.... and so on. What we have seen so far that there is a desired goal for nanotechnology to produce a system able to inexpensively synthesize most ‘diamondoid’ i.e. strong and other type of structures and materials. Therefore, the intention for nanotechnology at the present is a general purpose programmable manufacturing system which uses ‘positionally’, controlled highly reactive tools in vacuum and is able to self-replicate. The design complexity of artificial self-replicating systems need not be excessive. One of the simplest ‘self replicating systems’ (when executed, it prints itself out on the standard output) is the following one line C program: main(){char q=34,n=10,*a="main(){char q=34,n=10,*a=%c%s%c;printf(a,q,a,q,n);}%c";printf(a,q,a,q,n);}

[1]

The question still remain: Is it possible to design system able to build an assembler with hundreds of millions or billions of atoms with no atom out of place? If we can do that, then the error rate must be low, or if this is not possible then we must have an error detection and correction system in operation at the same time. At the present, SPMs [2] can build a small part of the size of possible assemblers and have error rates high that will need to use an error detection and correction methods along side it. Another problem scientists discovered is the difficulty to build an assembler within a vacuum and therefore various solutions were put forward to overcome this problem. One of these methods is called ‘building block based nanotechnology’. That is building other materials from large molecular building blocks in large numbers in order to reduce the number of assembly steps. The whole process is completed within a soluble solution to overcome the need for a vacuum.

Solution based

systems could use positional control to assemble the building blocks, but can also use the methods of self-assembly.

Prof. Drexler raises an interesting question: ‘A microscopic, one-celled form of algae may help provide some of the answers to a long-standing question in nanotechnology research: How does one coax molecules to self-assemble into a desired structure?’ He answers the question by saying first that the understanding of the above could lead to the development of ‘nano-assemblers’ devices.

Najib Altawell

[1] (From Self-reproducing programs, Byte magazine, August 1980, page 74. also you can refer to Introduction to the Theory of Computation by Michael Sipser, 1996, Chapter 6) [2] SPM: Scanning Probe Microscopy

© Altawell 2008