# Gold Nanoparticles and Nanorods in Nuclear Medicine: A Mini Review
###### Abstract
\(\alpha\) particle-emitting radionuclides are of considerable interest for radionuclide therapy because of their high cytotoxicity and very short path length. The most common use of radiometabolic therapy is the treatment of thyroid-related diseases [42; 43]. Some other radionuclides emitting \(\beta\)-particles are also used in radiotherapy departments for the low-dose rate \"brachytherapy\" of some tumors, particularly prostate cancer [44; 45; 46]. Knowing this panorama, we can certainly say that the traditional health care and medical technology might be deeply influenced by the application of nanotechnology to nuclear medicine principles. A great impact on functional diagnosis and radiometabolic treatment can be expected, although the clinical applications are still at an initial phase. In fact, many nanoproducts have been developed, and the Food and Drug Administration (FDA) is receiving many requests for the approval of nanomaterials conjugated with approved drug and radioactive agents [47]. Nanoradiopharmaceuticals show excellent promise in nuclear imaging and/or radiometabolic therapy. Their potentials offer more possibilities. It can be possible to develop nondimensional systems of existing radiopharmaceuticals or build engineered systems that combine a nanoparticle with the radiopharmaceutical, a tracer, and a target molecule and still develop selective nanodetection systems. Among others, a main advantage of nanosized radioactive formulations is the presence of numerous radioactive atoms within a single nanoparticle. The conventional methods will allow only one tumor-avid biomolecule to carry one radioactive nuclide, but effective tumor therapy requires maximum radioactivity (effective payload) within the tumor site. The nanoparticles conjugated to tumor-avid biomolecules will be used as a Trojan horse to introduce a higher ratio of radioactive particles into the tumor. Thus, nanoparticles will become optimized drug delivery systems over a wide range of diseases, especially in cancer. Nanoparticles can usually be accumulated in tumor endothelial cells but in nonspecific ways, such as passive targeting by means of the enhanced permeability and retention (EPR) effect. The finding of the EPR effect is one of the greatest advances leading to the development of targeted antitumor therapy. In addition to the enhanced leakiness of tumorous vessels, the EPR effect is also because solid tumors have a tendency to lack functional lymphatics, limiting in that way the removal of extravasated nanomaterials from the target site. Unluckily, when we are in the presence of large tumors, the local drug delivery is impracticable, because in these cases, the tumors have poor vascularization. In the passive targeting, the drug's achievement is directly correlated to the circulation time. The nanoparticles' functionalization can also afford a stealth surface that would moderate the reticuloendothelial system (RES) recognition of NPs and extend the circulation half-life. RES consists of cells descending from the monocytes, which can achieve the phagocytosis of foreign compounds. It is well-known that 90% of the RES are in the liver. Even though the EPR effect affords the opportunity for targeting into the tumor, it is not applicable to low-vascular permeability cancers. In addition, passive targeting could be not enough for drug accumulation in tumors. Where EPR is weak, NPs should be willing to aid permeation beyond the vasculature and into the tumor environment. While dissimilar passive targeting demonstrates low tumor selectivity, active targeting produces a higher intratumoral accumulation of a nanocarrier and drug. Consequently, it is positive to develop active targeting systems that can selectively identify specific cells or tissues, attaching specific ligands such as antibodies, aptamers, peptides, and so forth, on nanocarrier surfaces [48; 49]. Among others, the gold-based nanomaterials have amazing features that make them very suitable and valuable in nanomedicine.