NANOPARTICLES AND THEIR USES
Nanotechnology began with advances in viewing and measuring the incredibly small. It then moved on to building structures at the nanoscale. Simple nanostructures are now being used for a variety of analytical purposes, and a second generation is being developed for clinical use.
As their name indicates, nanoparticles are particles of submicron scale—in practice, from 100 nm down to 5 nm in size. They are usually spherical, but rods, plates, and other shapes are sometimes used. They may be solid or hollow and are composed of a variety of materials, often in several discrete layers with separate functions. Typically, there is a central functional layer, a protective layer, and an outer layer allowing interaction with the biological world.
The central functional layer usually displays some useful optical or magnetic behavior. Most popular is fluorescence. The protective layer shields the functional layer from chemical damage by air, water, or cell components and conversely shields the cell from any toxic properties of the chemicals composing the functional layer. The outer layer(s) allow nanoparticles to be “biocompatible.” This generally involves two aspects, water solubility and specific recognition. For biological use, nanoparticles are often made water soluble by adding a hydrophilic outer layer. In addition, chemical groups must be present on the exterior to allow specific attachment to other molecules or structures (Fig. 7.8).
Nanoparticles have a variety of uses in the biological arena:
(a) Fluorescent labeling and optical coding
(b) Detection of pathogenic microorganisms and/or specific proteins
(c) Purification and manipulation of biological components
(d) Delivery of pharmaceuticals and/or genes
(e) Tumor destruction by chemical or thermal means
(f) Contrast enhancement in magnetic resonance imaging (MRI)