Biological Toxicities and Aggregation Effects of ʟ-Glycine and ʟ-Alanine Capped ZnS:Mn Nanocrystals in Aqueous Solution

Abstract

-Alanine. The ZnS:Mn-Gly and ZnS:Mn-Alananocrystal powders were characterized by XRD, HR-TEM, EDXS, ICP-AES, and FT-IR spectroscopy. Theoptical properties were measured by UV-Visible and photoluminescence (PL) spectroscopy. The PL spectrafor the ZnS:Mn-Gly and ZnS:Mn-Ala showed broad emission peaks at 599 nm and 607 nm with PL efficienciesof 6.5% and 7.8%, respectively. The measured averag e particle size from the HR-TEM images were 6.4 ± 0.8nm (ZnS:Mn-Gly) and 4.1 ± 0.5 nm (ZnS:Mn-Ala), which were also supported by Debye-Scherrer calculations.In addition, the degree of aggregation of the nanocrystals in aqueous solutions were measured by a hydro-dynamic light scattering method, which showed formation of sub-micrometer size aggregates for bothZnS:Mn-Gly (273 ± 94 nm) and ZnS:Mn-Ala (233 ± 34 nm) in water due to the intermolecular attractionbetween the capping amino acids molecules. Finally, the cytotoxic effects of ZnS:Mn-Gly and ZnS:Mn-Alananocrsystals over the growth of wild type E. coli were investigated. As a result, no toxicity was shown for theZnS:Mn-Gly nanocrystal in the colloidal concentration region from 1 µg/mL to 1000 µg/mL, while ZnS:Mn-Ala showed significant toxicity at 100 µg/mL.Key Words : ZnS:Mn nanocrystal, Glycine capping, Alanine capping, Cytotoxicity, AggregationIntroductionThe synthesis of nano-sized low-dimensional semicon-ductor nanocrystals and their applications have been one ofthe most attractive research subjects for the last fewdecades.