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

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

7.4.2.4 Chemical Inmessaging

Ingestion or inhalation of chemical messenger molecules is another way the patient can control the flow of information and commands into his body. The patient could provide the desired data or commands to a desktop manufacturing appliance, which appliance then encodes the information onto billions of copies of a hydrofluorocarbon messenger molecule suspended in a carrier fluid or solid pill, which the patient subsequently inhales or ingests. Messages up to ~10⁹ bits may be distributed throughout the body in ~one circulation time (~60 sec), a data transfer rate up to ~10⁷ bits/sec. Patients without access to personal manufacturing appliances could be given fluid ampules, standardized pill sets or inhalers whose contents are designed to trigger specific predetermined nanorobot behaviors. Such sets must contain personal security codes to prevent their unauthorized use on other patients (see Chapter 12).

A related technique for chemical inmessaging is to allow naturally inhaled or ingested molecules (e.g., gustation or olfaction) to trigger specific nanorobot actions. For example, if continuously circulating detoxification nanorobots are programmed to begin removing alcohol from the bloodstream whenever the presence of garlic compounds is detected, then the patient can voluntarily trigger the detox response by sniffing or chewing a clove of garlic. (A population of 10¹² bloodborne nanodevices with aggregate storage volume ~6 cm³ can reduce serum alcohol from 0.2% to 0.005% in ~1 second by prompt onboard sequestration, followed by metabolization of the entire inventory in ~10 minutes within a systemic caloric budget of ~200 watts, although outflows from ethanol-soaked body tissues into the bloodstream and other factors complicate the process; see Chapters 19 and 25.) Similarly, nanorobots with selected chemical sensors stationed in the vomeronasal organ,¹⁹⁷¹ vallate papillae or olfactory epithelium could directly detect and respond to specific flavors, perfumes, pheromones¹⁹⁷² or other chemical substances -- even molecules which humans are normally incapable of tasting or smelling, including artificial or engineered substances.

Binary message sequences employing the five basic gustatory stimuli (Section 7.4.6.4) must use one of the stimuli as a positional spacer to avoid confusion. For example, a patient sipping the 8-taste sequence "sweet (1), salty (/), sweet (1), salty (/), sour (0), salty (/), sweet (1), salty (/)" has just transferred the binary sequence "1101" into his body. ("Salty" is used as the spacer because salt sensitivity is most widely distributed over the surface of the tongue. "Sour" is used because saltiness partially suppresses perception of bitterness, and because sweet and bitter taste messages are transmitted by the same transducer protein, called a-gustducin.) This inmessaging modality is probably limited to ~0.1 bit/sec but may be boosted considerably by employing complex artificial gustatory stimuli (akin to messenger molecules) which only lingually-embedded nanorobot sensors can detect.

Human olfactory receptors can probably detect ~1000 different smells (Section 7.4.6.4); exposure to a new olfactory stimulus every 1-10 seconds, with each smell worth log₂(1000) = 10 bits/symbol, allows information transfer up to ~1-10 bits/sec. Individual chemical assay nanorobots that can detect ~10⁷ different molecules (Section 4.2.4) allow greater diversity and specificity of signal carriers, but at most only ~double the bit rate because log₂(10⁷) = 23 bits/symbol. However, the bit rate using long-chain digitally coded artificial messenger molecules is vastly higher, and probably only thermogenically (heat of manufacture and access; Sections 7.2.1.8 and 7.2.6) and biocompatibility (Chapter 15) limited.

Last updated on 19 February 2003