# Zn Doping Improves the Anticancer Efficacy of SnO2 Nanoparticles
## 1 Introduction  
Nanoparticles (NPs) have been applied in various ways, such as gas sensing, environmental remediation, and biomedical research, due to their unique physicochemical properties [1, 2]. They are also utilized in developing biomaterials for tissue engineering and regenerative medicine. Moreover, NPs have emerged as promising candidates for therapeutic use in a wide range of disorders. Targeted treatments, such as photothermal therapy, photodynamic therapy, and gene therapy, may be facilitated by their applications. Different medications based on NPs have recently entered the market, and many of them are undergoing different phases of preclinical and clinical trials [3, 4, 5].  
Among these NPs, metal oxide NPs (MONPs), such as Bi2O3, SnO2, TiO2, WO3, and In2O3, have received significant attention with regards to their potential application. They exhibited several advantageous properties that make them highly promising for biomedicalapplications due to their high stability, easy preparation, and the ability to easily control their size and shape [6; 7; 8; 9]. Tin oxide (SnO\({}_{2}\)) is a semiconductor material with a broad band gap and n-type conductivity. It has a band gap of 3.6 eV and possesses good electrical, optical, and thermal properties [10; 11]. These metal oxide NPs can be prepared using various approaches. Among these approaches, sol-gel [12], Co precipitation [13], hydrothermal methods [14], thermal decomposition [15], and microwave-assisted reactions [16] have been used to synthesize SnO\({}_{2}\). Currently, researchers have applied several dopant metals, including Er\({}^{3+}\), Mn, Co, Ni, and Fe, to enhance the physicochemical properties of SnO\({}_{2}\)[17; 18; 19; 20]. For example, [PERSON] et al. [21] investigated that Cu and Fe dopants change the crystallite size and electrical conductivity of SnO\({}_{2}\) NPs. Furthermore, [PERSON] et al. [22] reported that the reduction in band gap energy of SnO\({}_{2}\) NPs observed with increasing the amount of Zn.  
Studies suggested that tin oxide (SnO\({}_{2}\) NPs) induces cytotoxicity, membrane damage, and oxidative stress in various biological systems. A study conducted by [PERSON] et al. [23] showed that SnO\({}_{2}\) NPs cause cytotoxicity in human breast cancer cells by triggering oxidative stress. [PERSON] et al. [24] showed that SnO\({}_{2}\) NPs induced oxidative stress with increasing intracellular ROS accumulation. [PERSON] et al. [25] showed that SnO\({}_{2}\) NPs, produced using laser ablation, suppressed the growth of MCF-7 breast cancer cells. [PERSON] et al. [26] found that SnO\({}_{2}\) NPs caused high cytotoxicity and oxidative stress in tobacco cell cultures with Ag doping. [PERSON] et al. [27] revealed that increasing Ce-dopant concentrations improved the anticancer activity of SnO\({}_{2}\) NPs compared to pure SnO\({}_{2}\) NPs. our previous study [PERSON] et al. [28] investigated that pure SnO\({}_{2}\) NPs and SnO\({}_{2}\)/RGO NCs induce cytotoxicity against liver (HepG2) and lung (A549) cancer cells.  
The objective of this study was to examine how the addition of Zn affects the ability of SnO\({}_{2}\) NPs to inhibit the growth of cancer cells. A modified sol-gel process successfully prepared pure and Zn-doped SnO\({}_{2}\) NPs. Various techniques, including XRD, TEM, FE-SEM, EDX, FTIR, UV-vis, and PL spectrometry, were carefully used to examine the properties of synthesized NPs. This biological study was focused on examining the anticancer properties of nanoparticles (NPs) against MCF-7 cells. The biocompatibility of produced NPs was also examined on HUVECs. These results suggest that the cytotoxicity of Zn-doped SnO\({}_{2}\) NPs against MCF-7 cells were higher than pure SnO\({}_{2}\), and they have good biocompatibility with normal HUVECs.