Biomedical devices

The devices considered in this section fall into the category of nanobiotechnology, also known as nanomedicine, defined as the application of nanotechnology to human health.One of the most attractive candidate tasks for a radically new approach is the sequencing ofthe human genome. The growing fund of medical experience concerning individual patients’responses to pharmaceutical drugs is revealing significant differences between individuals, whichin many cases might be due to differences in DNA sequence. Despite the tremendousboost to the technology of DNA sequencing that came from the international project to sequencethe (putatively prototypical) human genome, the basic methods applied were the conventionalbiochemical ones; the vast increase in throughput was achieved through massive parallelizationand automation.
The four different DNA “bases” (or nucleotides, symbolized as A,C,G,T) differ not only in the chemical nature, but also in their physical nature, most significantly as regards size and shape.One of the early motivations for developing the atomic force microscope was the hope that thesephysical differences could be revealed by rapidly scanning a single strand of DNA. Although theresolution, at least in the presence of liquid water, has so far proved to be inadequate, alternativeapproaches with the same end in view are being intensively investigated. The favoured schemeis to pass the DNA strand through a nanopore while measuring ionic conductance (of theelectrolyte solution in which the DNA is dissolved), either along or across the pore, with theresolution of a single base. The different nucleotides can be thus distinguished, but it is difficultto capture the DNA and drive it through the pore.
The flagship nanomedical system (rather than device) is the “nanobot”, an autonomous robotenvisaged to be about the size of a bacterium (i.e., about one micrometre in diameter), andcontaining many nanodevices (an energy source, a means of propulsion, an information pro-cessor, environmental sensors, and so forth). When engineering such devices it is importantto note the environment in which they must operate: viscous (highly dissipative), dominatedby friction and fluctuations (Brownian motion), and in which inertia plays a negligible role.This is in contrast to the familiar macroscopic mechanisms that follow Newton’s laws: for thenanobot, force is not given by the product of mass and acceleration, but by the product of thecoefficient of friction and its velocity, together with superimposed random fluctuations. Anyself-propelling nanobot is therefore likely to resemble a motile bacterium rather than a deviceequipped with nanoscale oars or paddles.
Source: Jeremy Rameden," Nanotechnology " 2009