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

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

8.4.4 Microbiotagraphics

While high-speed nanomedical prophylactic measures against pathogens will be readily available (e.g., Section 10.4 and Chapter 19), in some cases the physician may wish to obtain an infection map before beginning treatment. It may also be useful to prepare maps of particular symbiotic, commensal, or parasitic bacterial species, or native mobile cellular elements, in the human body, whether for scientific or for diagnostic purposes.

For example, leukocytes and macrophages are readily recognized (Section 8.5.2.2) and could be statistically sampled to produce a crude whole-body leukographic map. A fleet of 2 trillion mapping nanorobots evenly distributed throughout a 0.1 m³ body volume gives each nanorobot a patrol volume of 50,000 micron³ (~1 capillary volume). At 310 K, a 1-micron nanorobot of normal density has an average thermal velocity of ~500 microns/sec (Eqn. 3.3). Assuming a cross-sectional area of ~1 micron², in 1 second a motile device traveling at this speed may trace out a nonrepeating zigzag path ~500 microns in length, or ~1% of its patrol volume, even while diffusing an additional radial distance of only DX ~ 1 micron (Eqn. 3.1). During its zigzag course, the device may collide at least once with ~1% of the motile body cells or microbiota present within the patrol volume. If ~10 collisions are required to ensure a positive identification of a cellular coat, then ~0.1% of the entire target cell population present in the patient's body may be physically sampled, positively identified, affirmatively counted, and directly associated with a specific map voxel in ~1 sec -- a sufficient statistical sample for most purposes, even given the likelihood of substantial double-counting. A whole-body white-cell-count map to ~1 cm³ voxel resolution requires ~10⁶ bits to describe and may be retrieved by the physician in <~1 sec using an in vivo mobile acoustic communication network; a ~1 mm³ resolution map (~10⁹ bits) fine enough to discover even the smallest macroscale infection site requires ~100-1000 seconds to outmessage in this manner. A sequence of readouts at regular intervals provides a clear strategic overview of the developing infection -- some bacterial infections cause a selective increase in neutrophils, while infections with some protozoa and other parasites cause a selective increase in eosinophils.⁵³¹

Whole-body vascular (e.g., bloodstream only) surveys of red cells, white cells, platelets or pathogens will proceed ~10 times faster using a nanorobot fleet of similar number density, owing to the reduced search volume, though at the cost of slightly increased onboard computational complexity needed to compensate for the moving reference frame.

Discussion of possible protein coat marker modifications that bacteria or other pathogens might evolve in a nanomedical technology-rich treatment environment as a defensive tactic is deferred to Chapter 17.

Last updated on 20 February 2003