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.
Highlights
The surface organic ligands have profound effect on modulation of different physicochemical parameters as well as toxicological profile of semiconductor nanocrystals (NCs)
In order to verify the effect of the supporting ligand on Zinc oxide (ZnO) NCs’ physicochemical properties and biological activity toward lung cells, three commercially available alkoxyacetic acids (AAA-H) were selected as pro-ligands for the preparation of ZnO NCs coated with the monoanionic AAA ligands that act as native capping agents in the two-step one-pot self-supporting organometallic (OSSOM) method, i.e. methoxyacetic acid (MAA-H), previously applied 2-(2-methoxyethoxy)acetic acid (MEAA-H)[17] and 2-[2-(2-methoxyethoxy)ethoxy)acetic acid (MEEAA-H) (Fig. 2)
In the foregoing account, we presented the results describing the organometallic synthesis of a series of colloidal ZnO NCs coated with various monoanionic alkoxyacetate ligands with strongly anchoring the carboxylate head-group and different ether chain lengths
Summary
The surface organic ligands have profound effect on modulation of different physicochemical parameters as well as toxicological profile of semiconductor nanocrystals (NCs). We wondered how minor changes in the backbone of alkoxyacetate ligands will affect physicochemical properties and nano-specific toxicity defined by structure-property relationship of ligand coated ZnO NCs prepared via the OSSOM method Towards this aim, we report on (i) the preparation of colloidal and bio-stable ZnO NCs coated by alkoxyacetate ligands with different tail length and strongly anchoring the carboxylate head-group along with the influence of applied coating on (ii) the NC’s properties including the inorganic core size and the hydrodynamic diameter, solution-stability as well as optical parameters, i.e. photoluminescence (PL) quantum yield and PL decay times, and (iii) their biological activity toward lung cells. The toxicological effect of ZnO NCs on normal human (MRC-5) and cancer human (A549) lung cells was evaluated by determination and comparison of the cell metabolic activity at different NCs doses, ability to ROS generation and corresponding cell death mechanism
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