# Doped Zinc Oxide Nanoparticles: Synthesis, Characterization and Potential Use in Nanomedicine
## 4 Use of Doped ZnO NPs in the Biomedical Field
### Doped ZnO as Therapeutics against Cancer  
ZnO nanoparticles present interesting properties useful for effectively fighting cancer as well. ROS generation and the ZnO particles dissolution are the main mechanisms responsible for cell and bacterial death. Therefore, it can be potentially toxic for tumoral cells. For ZnO dissolution, the role of Fe doping as a stabilizer for the ZnO crystal lattice has been highlighted in Section 4.1, leading to a decreased dissolution rate of the nanoparticle. This has been proven to also inhibit tumoral cell growth. As a matter of fact, tumoral cells appeared to be more sensitive to the presence of ZnO than healthy ones [283; 284]. By finely tuning the dissolution rate of ZnO nanoparticles with Fe doping, it was possible to reduce the toxicity to an optimal value so as to be harmful for cancer cells without damaging healthy cells [204]. The promising results obtained in in vitro tests gave the basis to perform a preclinical study on a rodent model for evaluating the antitumor response: pure 2 wt.% and 10 wt.% Fe-doped ZnO nanoparticles were tested in mice, finding again a reduced amount of free zinc ions being released, and a decreased tumor growth in the presence of the Fe-doped ZnO NPs. In particular, the tumor (KLN-205) was inoculated subcutaneously in mice and, after 10 days of treatment with pure ZnO NPs, mice displayed signs of toxicity to force the authors \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Ref.**} & \multirow{2}{*}{**Dopant**} & \multirow{2}{*}{**Dopant**} & \multirow{2}{*}{**Bandgap (eV)**} & \multirow{2}{*}{**Dopant**} & \multirow{2}{*}{**Saturation**} \\  & & & & & **Magnetization** \\  & & & & **(emu/g)** \\ \hline
[259; 260; 261] & Cu & 0, 10\% & 3.35, 3.30, respectively & & 0.05–0.20 & 0.011–0.063 \\  & & & & mol.\% & & \\
[180; 262] & Fe & Zn\({}_{1-\text{x}}\)Fe\({}_{\text{O}}\) (x = 0, & 3.243, 3.236, 3.216, & & \\  & & 0.01, 0.04, 0.05, 0.06) & 3.197, 3.195, & x = 0.20 & 1.74 \\
[263] & Cr & 0.00 to 4.63 at.\% & from 3.26 to 3.15 & 2.49 at.\% & 4.86 \\
[175] & Co & 0, 5, 10 at.\% & 3.10, 3.17, 3.24, & 5 at.\%, 10 at.\% & 1.42, 1.75 \\
[264; 265; 266; 267] & Mn & 0, 3, 5, 10, 15 mol.\% & 3.31, 3.35, 3.38, 3.40, & 3.3 mol.\%, 4.2 & \\  & & 3.42, respectively & mol.\% & 0.00123, 0.015 \\
[268] & Ni & Zn\({}_{1-\text{x}}\)Ni\({}_{\text{x}}\)O (x = 0, & 3.28, 3.32, respectively & x = 0.05 & 2.9–2.8 \\
[269; 270] & Al & 0, 2 at.\% & 3.07, 3.12, respectively & 0.03 at.\% & 0.012 \\
[138; 271] & Mg & 0, 2.5\%, 5\%, 7.5\% & 3.36, 3.27, 3.13, 3.04, & 3% & \(1.05\times 10^{-3}\) \\  & & & respectively & & \\
[272] & Nd & ZnO, Zn\({}_{0.97}\)Nd\({}_{0.03}\)O & 3.34, 3.12, respectively & x = 0.03 & 0.67 \\  & & & & 0.45, 0.363, & \\
[273; 274] & Sm & 0, 1, 3, 5 mol.\% & 3.27, 3.25, 3.10, 3.05, & 0%–8\% & 1.694, 3.613 and \\  & & & respectively & & 2.197 emu/cm\({}^{3}\) \\
[275; 276] & Eu & 0, 1, 3, 5 mol.\% & 3.18, 3.05, 3.00, 2.94, & & 10\% & 0.040 \\  & & & respectively & & \\
[277] & Tb & Zn\({}_{1-\text{x}}\)TbxO (x = 0, & 3.35, 3.31, 3.30, 3.28, & x = 0, 0.02, 0.05, & 0.0042, 0.0276, \\  & & 0.02, 0.05, 0.1) & respectively & 0.1 & 0.0359, 0.0519 \\
[117; 278] & Gd & 0, 3, 6\% & 2.71, 2.74, 2.98, & 1.1\%, 3.5\%, and & 0.0001, 0.05, \\  & & & respectively & 5.1\% & 0.0032 \\
[279; 280] & La & 1, 5 wt.\% & 3.12, 3.18, respectively & 0, 1 mol.\% & 0.102, 0.232 \\  & & & & & \(1.895\times 10^{-3}\), \\  & & & & & \(0\), 0.96, 1.96, & \(31.612\times 10^{-3}\), \\
[281; 282] & Ce & 0, 1, 3 and 5 at.\% & 3.21, 3.10, 3.08, 2.96, & 2.52 and 3.12 & \(26.818\times 10^{-3}\), \\  & & & & at.\% & \(26.136\times 10^{-3}\), \\  & & & & & \(23.608\times 10^{-3}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Doped ZnO: optical and magnetic properties. to stop the experiment with pure ZnO for ethical reasons. Figure 10 shows the growth of the tumor for the 2 wt.% and 10 wt.% Fe-doped ZnO NPs and the control (saline solution) treatments.