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

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

7.2.1.2 Diffusion-Limited Broadcast Rate

Given I_message ~ 10⁹ bits for r_message = 0.2 micron from Eqn. 7.2, it is clear that onboard stores of messenger molecules will be quickly exhausted at the highest broadcast bit rates unless the communication system architecture makes substantial use of messenger molecule recycling. Without recycling, emission of hydrofluorocarbon message molecules is fluorine-limited, because carbon and hydrogen atoms are readily available from glucose and water molecules. The bloodstream concentration of fluoride is ~4.5 x 10^-7 gm/cm³ (Appendix B) or ~1.4 x 10²² F atoms/m³. From Eqn. 3.4, the maximum diffusion current to the entire surface of a spherical nanodevice of radius R = 1-micron and diffusion constant D ~ 2 x 10^-9 m²/sec (est. from Table 3.3) is J = 3.6 x 10⁸ F atoms/sec or 1.1 x 10^-17 kg/sec, enough fluorine to manufacture 2.7 x 10^-17 kg/sec representing a continuous long-term maximum broadcast rate of 'I ~ 7.2 x 10⁸ bits/sec of (CHX)_n 1-bit/unit hydrofluorocarbon messenger molecules.

Even in the unlikely event that all 8.3 x 10²² atoms of fluorine present in the human body (Table 3.1) were somehow converted to hydrofluorocarbon messenger molecules and released into the bloodstream simultaneously, the bloodstream concentration would reach ~1.2 gm/liter, well below the ~700 gm/liter LD50, though admittedly exceeding the ~0.1 gm/liter limit that occasionally triggers anaphylactoid-type reactions.

In 1963, Bossert and Wilson⁷⁰³ completed the first systematic analysis of chemical communication in the context of animal olfactory communication in air, later extended by Bossert⁷²⁵ in an analysis of maximum possible bit rates. In the following discussion, their results are adapted to the problem of in vivo chemical communication among medical nanodevices.

Last updated on 18 February 2003