Nanomedicine, Volume I: Basic Capabilities

© 1999 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Nanomedicine, Volume I: Basic Capabilities, Landes Bioscience, Georgetown, TX, 1999 Organic and Bioelectronic Computers

Many organic materials may be useful in electronic computing. Electrical conduction in synthetic organic molecules is well known1761,1906-1909,3125-3128 and already exploited in liquid-crystal displays of laptop computers.1925 Doped polyacetylene is a conducting plastic with a carbon backbone; undoped, it is an insulator. There are many other known families of conducting polymers such as polyaniline, which includes nitrogen atoms in the backbone, and polythiophene, which includes sulfur.1833 Three-dimensional interconnect arrays of organic conducting polymers have been fabricated;1839 conductivity is higher along a chain than between chains, so sheets of oriented chains can produce relative conductivity anisotropies as high as 100-1000.1927 An all-plastic transistor has been built.1935 Organic transistors have been used as the active semiconducting element in thin-film transistors fabricated with organic-material thicknesses ranging from 5-150 nm,1842 and organic microscale transistors and other organic devices may exploit bulk-effect electron transport just like silicon-based semiconductor devices.1923 Conjugated polymer poly(1,6-heptadiester) was employed to make an optical correlator with a peak processing rate of 3 x 1016 operations/sec.1841 Spin-transition polymers could serve as thermal sensors or memory devices with the theoretical ability to store one bit in a ~4 nm cube (~2 x 107 bits/micron3 storage density) with ~GHz addressing speeds at room temperature.1840 Other organic polymers possibly useful in logic circuits have been investigated.2899

Natural biological materials may also be useful in electronic computing,1777,1925,3129 particularly because of the ability of biological materials to self-assemble. Biomolecular electronics is a subfield of molecular electronics that investigates the use of native as well as modified biological molecules (chromophores, proteins, etc.) in place of the organic molecules synthesized in the laboratory.1777 In theory, a three-dimensional DNA or protein scaffolding could be self-assembled, with bacteriorhodopsin, ferritin and magnetite, or related bioelectromagnetic molecules inserted into precise locations within the structure to produce a crystal lattice bioelectronic or biooptoelectronic nanocomputer. DNA already has been used as an atomic scaffold upon which to build silver wires ~100 nm in diameter1961 and has been decorated with fullerenes.3024 Self-assembly can generate membrane-based1931,1932 and biotubule-based1926 devices, and site-directed mutagenesis is a valuable tool for high-resolution protein device engineering.1933 Nucleotide sequence-specific electron transfer between metallic electron donor and acceptor complexes covalently or noncovalently intercalated into strands of B-DNA has been demonstrated.1934

Perhaps the best-known bioelectronic (and biochemical) computer is the neuron cell and its congeries -- the ganglia, nerve trunks, and brains. In 1997, David Stenger (NRL) and James Hickman (SAIC) were attempting to culture and link together neuronal cells to build a bioelectronic cell-based sensor "computer" for performing complex pattern-recognition tasks.1966,1967 In early 1999, W.L. Ditto at Georgia Tech announced the creation of a biological computer comprised entirely of leech neurons, that was capable of perfoming simple sums.3245 We can certainly imagine large numbers of cultured neurons arranged in artificial three-dimensional spatial patterns to produce a synthetic bioneural computer, but such a computer would operate at only ~KHz frequencies and would be very energy inefficient since each neuron consumes ~1010 kT per discharge (Section -- thus offering few advantages.


Last updated on 24 February 2003