Emerging role of radiolabeled nanoparticles as an effective diagnostic technique

Nanomedicine can be defined as the use of nanoparticles for diagnosis, monitoring physical and pathologic processes, for therapy, and for control of biological systems [1]. Nanoparticles are defined as structures that are nanometers in size (often smaller than 100 nm) [2-4]. As small structures, they extravasate through the endothelial cell layers and interact with the cell structures of various tissues, but they are also large enough to transport high payloads of therapeutic or diagnostic agents (e.g., radioisotopes for molecular imaging) [5]. In contrast to atoms and traditional molecules, nanomaterials have an immense available surface area per unit of volume and tunable optical, electronic, magnetic, and biologic properties. They can be engineered to have different sizes, shapes, chemical compositions, surface chemical characteristics, and hollow or solid structures [6,7].Nanoparticles can be made of materials of diverse chemical nature, the most common being metals, metal oxides, silicates, polymers, carbon, lipids and biomolecules. Nanoparticles exist in several different morphologies, such as spheres, cylinders, platelets, and tubes. Generally, they are designed with surface modifications tailored to meet the needs of specific applications [8]. When used for in vivo studies, nanoparticles are typically coated with a hydrophilic polymer on their surface. The most broadly used polymer is polyethylene glycol (PEG), which reduces their uptake by the reticuloendothelial system (RES) and increases circulation time when compared with uncoated counterparts [9-11]. In addition, with this approach, aggregation between particles and association with serum and tissue proteins are diminished. Furthermore, solubility in serum increases due to the hydrophilic character of ethylene glycol units. As a result, liver uptake for those particles is significantly lower than that of non-PEGylated nanoparticles, allowing nanoparticles to remain in the blood pool for an extended peri