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

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

3.5.7.5 Construction Costs

The active binding site of a receptor consisting of (2.7 nm)³ ~ 19 nm³ of structural atoms and constructed with 0.001-nm feature sizes in theory requires information from 2 x 10¹⁰ voxels (volume pixels) for complete description. However, there are only N_atom ~ 1000 atoms involved in the structure and their locations cannot be arbitrarily chosen. Atomic scale (~0.1 nm) resolution would require ~19,000 voxels; each voxel minimally requires an index number (~log₂(19,000) ~ 14 bits), an atomic identifier (~log₂(92) ~ 7 bits), and a charge identifier (~log₂(3) ~ 2 bits), for a total of 23 bits/voxel which gives 4 x 10⁵ bits/receptor at atomic scale resolution. Drexler¹⁰ estimates the number of configurational options per atom N_opt ~ 150; hence a description of the receptor could require as few as N_atom log₂(N_opt) ~ 7 x 10³ bits.* Assuming energy dissipation of ~3 zJ/bit for rod logic register reading¹⁰ or ~kT ln(2) (Eqn. 7.1), then each time the receptor description is retrieved, stored or processed may require a minimum energy dissipation of ~10⁴-10⁶ zJ. Reversible computing may reduce this energy requirement by a factor of 10-100 or more (Section 10.2.4.1). Construction of a receptor containing ~1000 atoms using the nanomanipulator arm mentioned in Section 3.4.3 requires ~10^-2 sec and consumes ~0.001 picojoule (~10⁶ zJ) of mechanical energy.

* Higher level descriptions may allow considerable additional information compaction, as for instance where a 30-bit word indexes a single receptor structure stored in a library containing perhaps 10⁹ distinct designs.

Last updated on 7 February 2003