Nanotechnology (derived from the Greek word nano meaning dwarf) is generally defined as the science and engineering of constructing and assembling objects on a scale smaller than one hundred nanometers. Nanotechnology is a multidisciplinary scientific field undergoing explosive development. Nanoparticles are colloidal systems of submicron ( > 1 μM) size that can be constructed from a large variety of materials in a large variety of compositions. Commonly defined nanoparticle vectors include: liposomes, micelles, dendrimers, solid lipid nanoparticles, metallic nanoparticles, semiconductor nanoparticles and polymeric nanoparticles. Nanoparticles have been considered as effective delivery systems for many reasons including: (i) sufficient physical and biological stability that may facilitate drug entrapment and controlled release; (ii) good tolerability of the components; (iii) simplicity of the formulation processing; and (iv) possibility of scaling up the formulation process. Therefore, nanoparticles have been extensively employed to deliver drugs, genes, vaccines and diagnostics into specific cells/tissues.
Site-specific delivery of drug receives a lot of attention because it can reduce drug toxicity and increase therapeutic effects. To solve the problem of site-specific targeting for the colloidal systems, some authors have attempted to increase the tissue specificity of colloidal drug carriers by coupling targeting agents. In recent years the improvement of drug therapy in terms of a more controlled body distribution to reduce side effects was focused. Different new drug carrier systems in the micro- and nanometer size range were generated to overcome these problems. In principle, four different schemes of drug targeting are conceivable: firstly, a direct application of the drug to the pathological site which in most cases is not possible; secondly, passive targeting depending on carrier system accumulation in areas with leaky vasculature showing an enhanced permeability and retention effect (EPR-effect); thirdly, employment of physical effects like varying pH values, differences in temperature or magnetic systems, and finally as the most promising strategy the use of specific vector molecules such as antibodies representing the most universal approach .