Abstract
A wide variety of nanomaterials have shown a lot of potential in biological and biomedical applications. Among these nanomaterials, semiconductor nanoparticles also known as quantum dots (QDs) have shown unique properties which makes them excellent candidates for bio applications. However, most of these QDs compositions are made up of heavy metals such as Cd, Pb and Hg whose toxicity has become a source of concern to both human and environment. Thus, the shift of interest from binary II-VI to ternary I-III-VI QDs in bioimaging applications. In this work, we hereby report the synthesis of water soluble NIR emitting AgInSe2/ZnSe QDs and AgInSe2/ZnS QDs. Initially, the synthesis of a non-toxic Se precursor (Na2SeSO3) at different synthetic parameters was investigated. Modified methods of Chen et al., (2013), Chen et al., (2014) and Kang et al., 2015 were explored for the synthesis of AgInSe2/ZnS QDs. The optical analysis indicated that modified Kang et al., method gave the the best optical properties in relation to emission width, intensity and stability . This method was also employed for the synthesis of AgInSe2/ZnSe QDs. The as-synthesized QDs were characterised using Ultra-violet visible (UV-Vis), photoluminescence (PL) spectroscopy, Fourier transform infrared transmission (FTIR), X-ray diffraction (XRD), Transmission electron microscope (TEM), Energy dispersive X-ray spectroscopy (EDS) and dynamic light scattering (DLS). The results showed good PL properties for AISe/ZnS and AISe/ZnSe QDs while the TEM analyses showed that the materials are small and spherical in shape with good crystallinity. Investigating the use of different indium precursors showed that indium acetate produced the best PL properties, while further optimization was required to improve QDs synthesized with indium nitrate. An Ag: In mole ratio of 1: 4 revealed good luminescence while higher or lower In, Ag ratios produced poor luminescence. Varying thiol and polymeric stabilizers showed that TGA + gelatin produced the best PL properties while the inability of the MPA vii ligand to completely dissolve In(ac)3 resulted in QDs with broad emission. The absence of thiol stabilizer resulted in no emission peaks. Purification of the QDs resulted in a particle with narrower emission peaks but with less stability compared to the unpurified material. In order to determine the toxicity of these QDs, the as-synthesised AISe/ZnSe QDs were tested against three cancer cell lines namely; Hela (cervical cancer), Hek 293 (kidney cancer), A549 (lung cancer) and one normal cell line; BHK21 (kidney fibroblasts). The cell viability study of this QDs showed the greatest toxicity towards the Hek293 kidney cancer cells, with only around 50 % viability across the different concentration range. The cell viability was above 75 % for the remaining cell lines at the different concentration range. Flourescence imaging study after an hour incubation showed that AISe/ZnSe QD accumulated around the cells but with no visible fluorescence for over 4-day incubation. This study demonstrates the optimum conditions required for the large-scale green synthesis of high quality AISe/ZnSe and AISe/ZnS QDs with good optical and structural properties, and their great potential as a good material for biological applications.
M.Tech. (Chemistry)