Facile Chemical Synthesis of Doped ZnO Nanocrystals Exploiting Oleic Acid

Abstract

Zinc oxide nanocrystals (ZnO-NCs) doped with transition metal elements or rare earth elements can be probed for magnetic resonance imaging to be used as a molecular imaging technique for accurate diagnosis of various diseases. Herein, we use Mn as a candidate of transition metal elements and Gd as a presenter of rare earth elements. We report an easy and fast coprecipitation method exploiting oleic acid to synthesize spherical-shaped, small-sized doped ZnO-NCs. We show the improved colloidal stability of oleate-stabilized doped ZnO-NCs compared to the doped ZnO-NCs synthesized by conventional sol–gel synthesis method, i.e., without a stabilizing agent, especially for the Mn dopant. We also analyze their structural, morphological, optical, and magnetic properties. We are able to characterize the persistence of the crystalline properties (wurtzite structure) of ZnO in the doped structure and exclude the formation of undesired oxides by doping elements. Importantly, we determine the room-temperature ferromagnetism of the doped ZnO-NCs. This oleate-stabilized coprecipitation method can be subjected as a standard procedure to synthesize doped and also co-doped ZnO-NCs with any transition metal elements or rare earth elements. In the future, oleate-stabilized Gd/Mn-doped ZnO-NCs can be exploited as magnetic resonance imaging (MRI) contrast agents and possibly increase the signal intensity on T1-weighted images or reduce the signal intensity on T2-weighted images.

Doped Zinc Oxide Nanoparticles: Synthesis, Characterization and Potential Use in Nanomedicine

“…It is worth noting that, despite transition metals dopants being the best choice to induce room temperature fRT) ferromagnetism in ZnO, gadolinium, an RE element, has been proven to successfully induce a magnetic behavior in ZnO nanoparticles [ 117 , 118 ]. In particular, RT ferromagnetism was observed for a film made of Gd:ZnO nanop articles, doped by low energy fon implantation method.…”

“…Mn is characterized by several oxidation states with a higher difficulty in controlling this parameter. In addition, in this case, the dopant agent is used to modify the optical, structural and magnetic properties of the resulting ZnO semiconductor [ 118 ]. The ferromagnetic behavior of Mn-doped ZnO was found to be dependent on the doping amount but without a linear relationship between the two parameters [ 123 ].…”

“…Tuning its dimensions and energy band-gaps, the corresponding optical properties can be properly optimized and interesting luminescent properties can be gathered as in the case of ZnO quantum dots [ 163 , 222 ]. Moreover, as already stated, the inclusion of transition metals in the crystal lattice confers on ZnO a magnetic behavior, paving the way to its exploitation as a contrast agent in magnetic resonance imaging [ 118 ].…”

Iron-Doped ZnO Nanoparticles as Multifunctional Nanoplatforms for Theranostics

“…Indeed, in its pure form, ZnO presents a diamagnetic behavior at room temperature [32,33]. However, it is possible to induce a diamagnetic to paramagnetic or ferromagnetic transition by introducing selected atoms, such as manganese [34,35], gadolinium [36] or iron (Fe) [37], that are able to carry magnetic dipoles to the system [38]. In these cases, the doped ZnO NPs revealed interesting magnetic behaviors and, hence, bio-imaging properties particularly useful for magnetic resonance imaging (MRI) applications.…”

ZnO NANOPARTICLES: SYNTHESIS AND EVOLUTION

“…As such new methods for synthesis of nanoparticles of various dimensions are needed. Chemical synthesis offers a way to synthesize nanoparticles in an inexpensive and easy way without the use of specialized equipment [10,11]. In this case, it also allows for use of environmentally friendly materials which is crucial in the above mentioned fields.…”