ZnO nanocrystals derived from organometallic approach: Delineating the role of organic ligand shell on physicochemical properties and nano-specific toxicity

Abstract

The surface organic ligands have profound effect on modulation of different physicochemical parameters as well as toxicological profile of semiconductor nanocrystals (NCs). Zinc oxide (ZnO) is one of the most versatile semiconductor material with multifarious potential applications and systematic approach to in-depth understand the interplay between ZnO NCs surface chemistry along with physicochemical properties and their nano-specific toxicity is indispensable for development of ZnO NCs-based devices and biomedical applications. To this end, we have used recently developed the one-pot self-supporting organometallic (OSSOM) approach as a model platform to synthesize a series of ZnO NCs coated with three different alkoxyacetate ligands with varying the ether tail length which simultaneously act as miniPEG prototypes. The ligand coating influence on ZnO NCs physicochemical properties including the inorganic core size, the hydrodynamic diameter, surface charge, photoluminescence (quantum yield and decay time) and ZnO NCs biological activity toward lung cells was thoroughly investigated. The resulting ZnO NCs with average core diameter of 4-5 nm and the hydrodynamic diameter of 8-13 nm exhibit high photoluminescence quantum yield reaching 33% and a dramatic slowing down of charge recombination up to 2.4 µs, which is virtually unaffected by the ligand’s character. Nano-specific ZnO NCs-induced cytotoxicity was tested using MTT assay with normal (MRC-5) and cancer (A549) human lung cell lines. Noticeably, no negative effect has been observed up to the NCs concentration of 10 µg/mL and essentially very low negative toxicological impact could be noticed at higher concentrations. In the latter case, the MTT data analysis indicate that there is a subtle interconnection between inorganic core-organic shell dimensions and toxicological profile of ZnO NCs (strikingly, the NCs coated by the carboxylate bearing a medium ether chain length exhibit the lowest toxicity level). The results demonstrate that, when fully optimized, our organometallic self-supporting approach can be a highly promising method to obtain high-quality and bio-stable ligand-coated ZnO NCs.

From Uncommon Ethylzinc Complexes Supported by Ureate Ligands to Water-Soluble ZnO Nanocrystals: A Mechanochemical Approach

“…We would like to stress that the developed mechanochemical procedure allowed for a dramatic (>99%) decrease in reaction time compared to solution processes involving organozinc precursors, where ZnO NCs were obtained after approximately 5 days of stirring. 43,48 The reactions involving 1 4 or 2 lead to the formation of white crystalline powders exhibiting bright visible luminescence. The powder X-ray diffraction (PXRD) patterns of the postreaction mixtures (Figure 4b,f) revealed the formation of the wurzite phase of zinc oxide along with the free proligand (dcu-H or pu-H, respectively), and no traces of unreacted precursors were observed.…”

“…Previously, we reported the efficient mechanochemical synthesis of ZnO NCs from an inorganic oxo-zinc amidate precursor . In a number of our recent reports, we also highlighted the superiority of the organometallic precursor-derived nanocrystalline ZnO materials’ quality compared to materials prepared by traditional inorganic methodologies. − ,− Thus, we decided to explore the potential of mechanical force-induced transformations and evaluate the obtained ethylzinc ureates as model organozinc precursors of hybrid ZnO-based nanomaterials (Scheme , path ii ). To the best of our knowledge, this is the first attempt for the mechanochemical preparation of any hybrid nanomaterials from an organometallic precursor.…”

“…For more details concerning the mechanochemical process optimization, see the Supporting Information. We would like to stress that the developed mechanochemical procedure allowed for a dramatic (>99%) decrease in reaction time compared to solution processes involving organozinc precursors, where ZnO NCs were obtained after approximately 5 days of stirring. , …”

“…This surfactant-free self-supporting precursor-based strategy enabled the synthesis of ZnO NCs with a highly ordered and stable inorganic–organic interface and with tunable physicochemical properties mediated by the nature of coating ligands. The resulting NCs are characterized by ultralong electron recombination times, aggregation-dependent luminescence, and reduced toxicity , and in some instances are prone to unrestricted Cu-catalyzed click chemistry on the surface or form a chiroptically active surface . The above-mentioned solid-state and wet-chemical methodologies take advantage of the careful design of precursors, which in turn allowed for the optimization of the synthesis conditions as well as for the introduction of desired properties to the final hybrid material.…”

Band Gap Narrowing in Silane-Grafted ZnO Nanocrystals. A Comprehensive Study by Wide-Angle X-ray Total Scattering Methods

“…Zinc oxide (ZnO) nanoparticles exhibit uncommon optoelectronic properties attracting, over the last decades, a great deal of attention likely equated (for semiconducting oxide nanomaterials) only to that for titanium dioxide nanoparticles. Nanoscaling and nanostructuring have intriguingly expanded the well-known intrinsic properties of bulk ZnO (wide direct band gap, 3.37 eV, and high exciton energy, 60 meV) that make it an excellent candidate material for UV applications, − with gained interest in a wider range of fields (photovoltaics, catalysis, chemical and biosensing, light emitting devices, lasing, thermoelectrics, surface plasmonic resonance). − The material’s versatility is further favored by cost-effective large-scale ZnO production and low temperature processability, used jointly in a variety of preparation methods for the control over NP size and morphology, surface modification, stability, and toxicity issues. − …”