A Microwave-Assisted Synthesis of Zinc Oxide Nanocrystals Finely Tuned for Biological Applications.

Nadia Garino,Valentina Cauda,Andrea Falqui,Marta Canta,Tania Limongi,Alberto Casu,Micaela Castellino,Marco Laurenti,Bianca Dumontel,Luisa Racca

doi:10.3390/nano9020212

Abstract

Herein we report a novel, easy, fast and reliable microwave-assisted synthesis procedure for the preparation of colloidal zinc oxide nanocrystals (ZnO NCs) optimized for biological applications. ZnO NCs are also prepared by a conventional solvo-thermal approach and the properties of the two families of NCs are compared and discussed. All of the NCs are fully characterized in terms of morphological analysis, crystalline structure, chemical composition and optical properties, both as pristine nanomaterials or after amino-propyl group functionalization. Compared to the conventional approach, the novel microwave-derived ZnO NCs demonstrate outstanding colloidal stability in ethanol and water with long shelf-life. Furthermore, together with their more uniform size, shape and chemical surface properties, this long-term colloidal stability also contributes to the highly reproducible data in terms of biocompatibility. Actually, a significantly different biological behavior of the microwave-synthesized ZnO NCs is reported with respect to NCs prepared by the conventional synthesis procedure. In particular, consistent cytotoxicity and highly reproducible cell uptake toward KB cancer cells are measured with the use of microwave-synthesized ZnO NCs, in contrast to the non-reproducible and scattered data obtained with the conventionally-synthesized ones. Thus, we demonstrate how the synthetic route and, as a consequence, the control over all the nanomaterial properties are prominent points to be considered when dealing with the biological world for the achievement of reproducible and reliable results, and how the use of commercially-available and under-characterized nanomaterials should be discouraged in this view.

Highlights

In the last decade metal oxide semiconducting nanoparticles (NPs) have been receiving great interest in the field of biological applications due to their intriguing optical properties, low toxicity, good biocompatibility and their low cost [1]
In this work we report a new zinc oxide (ZnO) microwave-assisted solvothermal synthesis, optimized for biological uses
X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and optical analysis demonstrated similar physical-chemical properties of the zinc oxide nanocrystals (ZnO NCs) obtained by the two different synthetic procedures, in terms of surface chemistry and electron band gap

Summary

Introduction

In the last decade metal oxide semiconducting nanoparticles (NPs) have been receiving great interest in the field of biological applications due to their intriguing optical properties, low toxicity, good biocompatibility and their low cost [1]. It has been demonstrated how ZnO could be a promising material for therapeutic and diagnostic applications [2], showing high levels of drugs loading and a quite easy control over the following release [5,6] In this context, the optical, targeting and drug delivery properties of ZnO can be addressed by the combination of various synthetic procedures (sol-gel, sputtering, hydro-solvothermal, etc.) [7] and ZnO morphologies (nanowires, nanorods, nanobelts, desert roses and spherical nanoparticles) [8,9], together with surface functionalization approaches [2,10]. It is worth mentioning that many articles deal with the use of commercial particles (with the limit about their morphologies and size distribution) or did not report any specific detail about important synthesis aspects like the synthesis precursors, the surface chemistry, and sometimes the hydrodynamic size and z-potential [14,15]

Methods

Results

Conclusion