**5. Conclusion**

*Applications of Nanobiotechnology*

severely toxic to human carcinoma lung cells [80].

main cause of gold NP toxicity.

est distribution in the testis, liver, and brain [37].

Any toxicity induction of NPs is strongly related to NP base material, shape, size, and functional groups coated at their surface. The smaller NPs have a larger specific surface area which in turn leads to higher interaction cell components including nucleic acid, proteins, and carbohydrates. Also the smaller NPs can penetrate better into cells and interact higher with cells. Surface charge of NPs has strong correlation with their interaction with cells and absorbance. It is showed that the NPs with higher positive charge have higher cytotoxicity effects. Also NPs with positive charge are more toxic than negatively charged NPs [79]. The shape of NPs is the other critical parameter which largely affects their cytotoxicity and antiproliferative effects. For instance, the amorphous TiO2 NPs produced higher levels of oxidative stress and cell surface defects than anatase TiO2 NPs. Also the spherical Fe2O3 NPs had lower cytotoxic effects than rod-shaped ones. Also cytotoxicity is strongly dependent on the type of cells. For instance, although citrate-capped gold NPs were nontoxic to human liver carcinoma and hamster kidney cells, they were

NPs can easily penetrate into the cells and interact with cells' normal functions. ROS formation and consequently oxidative stress induction are the common side effects of metal NPs. The produced ROS disrupt normal cell function through attacking essential biological molecules including DNA, enzymes, and lipids. Peroxidation of membrane lipids; enhancing calcium entrance; release of calcium from intracellular stores, protein kinase C, and mitogen-activated protein kinase activation; and DNA damages are some of the main changes that lead to cell death after interaction with NPs [81, 82]. Furthermore the risk of early apoptosis upon exposure to some NPs such as ZnO and TiO2 has been demonstrated. Also CuO, NiO, TiO2, Fe3O4, ZnO, and Al2O3 NPs can arrest cell cycle and induce apoptosis. It is demonstrated that the phase of cell arrest depends on the type of cell and NPs. G2/M phase arrest is the most common type of cell arrest induced by metallic NPs. The induction of P53 pathway in NCM460 cells and cyclin-dependent kinase 1 downregulation in HaCaT cells after exposure to ZnO and cyclin B1 downregulation in A549 cells by TiO2 have been reported as the main causes of cell proliferation disruption [83, 84]. Many researches have been done on different cell lines and animal models for finding the mechanism of NP toxicity and physiological changes. The high absorption of gold NPs and their aggregation inside cells are probably the

Argyria is a condition of the skin and other organs' blue-gray discoloration as a result of long-time exposure to high levels of Ag NPs. Irritation, stomach pain, allergic reactions, and inflammation are reported as the main side effects of body exposure to high levels of Ag NPs [85]. TiO2 and ZnO NPs are widely being used in cream and lotions as sunscreen or materials for water- or stain-repellent properties. The cytotoxicity induction of TiO2 NPs through increasing reactive oxygen species and lactate dehydrogenase has been demonstrated [86]. It revealed that UV and visible light irradiation enhanced ZnO NP cytotoxicity power [87]. Also the Zn NPs were produced by microwave-assisted method, and its in vivo cytotoxicity and levels of distribution in different tissues have been evaluated. According to the obtained results, the produced Zn NPs were classified as nontoxic agents with high-

Several assays have been developed for the determination of NP toxicity both in vitro and in vivo. Proliferation assay which measures the active cell metabolism is the most popular method for determining the antiproliferative potency of NPs. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), XTT, thymidine incorporation, alamar blue, and clonogenic assay are the most popular methods for determining cell proliferation rate [88, 89]. DNA damage and apoptosis induction of NPs which are mainly due to generation of free radicals can be

**10**

NPs are becoming the spreadable part of medicine, and their uses are increasing every day. They exhibited promising biomedical uses regarding their special redox potentials, small sizes, high surface area, optical scattering, and fluorescence. Due to special biological effects of these compounds including significantly high antibacterial and antiproliferative effects against a wide range cells, their production and surface modification are increasing for reaching more effective agents. Besides they are able to be used as delivery devices for dispensing drugs and biological agents to specific sites. Owing to the advances in generation of multifunctional NPs, application of NP-based platforms is significantly increasing. While all NPs showed some degree of success in laboratory tests and some of them are now on the market, considering their potent environmental and biological side effects is necessary. Although several researches demonstrated the toxicity of different NPs, the cause of toxicity is mainly unknown. Any NP has its special toxicological characteristics, and there is not a comprehensive method for calculation or grading different NP toxicity. Production of NPs through methods with lowest dangerous side products, optimizing the NP production protocols, and doing both in vitro and in vivo tests of toxicity are the main steps toward production of NPs with lowest negative effects on the environment and human health. Short- and long-term toxicities of NPs and their pharmacokinetic and pharmacodynamic tests should be evaluated for FDA approval.
