Cytotoxicity of ZnO Nanoparticles Can Be Tailored by Modifying Their Surface Structure: A Green Chemistry Approach for Safer Nanomaterials

Abstract

ZnO nanoparticles (NP) are extensively used in numerous nanotechnology applications; however, they also happen to be one of the most toxic nanomaterials. This raises significant environmental and health concerns and calls for the need to develop new synthetic approaches to produce safer ZnO NP, while preserving their attractive optical, electronic, and structural properties. In this work, we demonstrate that the cytotoxicity of ZnO NP can be tailored by modifying their surface-bound chemical groups, while maintaining the core ZnO structure and related properties. Two equally sized (9.26 ± 0.11 nm) ZnO NP samples were synthesized from the same zinc acetate precursor using a forced hydrolysis process, and their surface chemical structures were modified by using different reaction solvents. X-ray diffraction and optical studies showed that the lattice parameters, optical properties, and band gap (3.44 eV) of the two ZnO NP samples were similar. However, FTIR spectroscopy showed significant differences in the surface structures and surface-bound chemical groups. This led to major differences in the zeta potential, hydrodynamic size, photocatalytic rate constant, and more importantly, their cytotoxic effects on Hut-78 cancer cells. The ZnO NP sample with the higher zeta potential and catalytic activity displayed a 1.5-fold stronger cytotoxic effect on cancer cells. These results suggest that by modifying the synthesis parameters/conditions and the surface chemical structures of the nanocrystals, their surface charge density, catalytic activity, and cytotoxicity can be tailored. This provides a green chemistry approach to produce safer ZnO NP.

Green Synthesis of Metal Nanoparticles via Natural Extracts: The Biogenic Nanoparticle Corona and Its Effects on Reactivity

“…At least one study has shown varied toxicology from ZnO nanoparticles depending on the synthesis route used: 27 it was determined that the two methods used to produce ZnO nanoparticles 4 resulted in different surface chemical properties, which accounted for different degrees of toxicity. 27 As another example, we previously developed a method to make composites consisting of silver or palladium nanoparticles on carbon microspheres using coffee solution, i.e., a natural reducing agent. 28 While the application of these materials as catalyst`s was within the acceptable range for the reactions used, they performed at a lower level than anticipated.…”

Green Synthesis of Therapeutic Nanoparticles: an Expanding Horizon

“…The author pointed out that such NPs easily penetrated into A549 cells and were toxic in dose dependent manner [91]. The effect of the surface properties on anticancer activity was very recently documented by Punnoose and co-workers using ZnO NPs [97]. In this study, green ZnO NPs showed higher toxicity to Hut-78 lymphoma T cells than chemically synthesized ones at the same dose (0.1 mM).…”

Influence of surface chemical properties on the toxicity of engineered zinc oxide nanoparticles to embryonic zebrafish

“…ZnO NPs are often coated with a variety of capping agents or surface ligands with differing chemical properties to functionalize the surface and improve stability against agglomeration and dispersibility in a given medium [16]. These surface alterations have the potential to alter their toxicity as a result of differences in the release of Zn 2+ ions and ROS production compared to bare ZnO NPs [17–18]. In addition, the behaviour of surface functionalized ZnO NPs may vary compared to non-functionalized (bare) ZnO NPs by altering stability and/or agglomeration, potentially altering bioavailability and toxicity to aquatic organisms [18–21].…”

“…These surface alterations have the potential to alter their toxicity as a result of differences in the release of Zn 2+ ions and ROS production compared to bare ZnO NPs [17–18]. In addition, the behaviour of surface functionalized ZnO NPs may vary compared to non-functionalized (bare) ZnO NPs by altering stability and/or agglomeration, potentially altering bioavailability and toxicity to aquatic organisms [18–21]. While the dissolution kinetics and agglomeration state of the ZnO NPs is known to influence the toxicity of the materials, this study aimed to determine if specific intrinsic features could be used in lieu of empirical data on the material’s behaviour.…”

“…Surface chemical ligands and capping agents are more closely related to the fate and effects of ZnO NPs than the core composition alone [18–19 22]. Thus, it is expected that surface chemical properties can be employed as descriptors to model the toxicity of various types of engineered ZnO NPs.…”