| dc.description.abstract | The main goal of this research is to investigate how different factors influence the induced optical activity of semiconductor nanoparticles (NPs) of various shapes and test the biological activity of NPs capped with chiral molecules on living cells. We also plan to study the influence of quantum dots (QDs) on the optical activity of a chiral molecule using the example of the photosensitizer chlorin e6 and to investigate the photodynamic efficiency of QD complexes with chlorin e6.
Chapter 1 of the thesis provides the introduction and describes the background theories and presents the literature review on QDs and chirality, including chirality at the nanoscale.
Chapter 2 provides experimental details for all procedures: the protocols of the synthesis and modifications of the quantum nanostructures; characterisation techniques used and the main principles of their functioning; as well as details of cell culturing and biological studies.
Chapter 3 is dedicated to the investigation of the dependence of optical activity and PL upon CdS shell thickness in a range of core-shell structured CdSe/CdS QDs capped with chiral ligands. For our study, five samples of CdSe/CdS were synthesised utilizing successive ion layer adsorption and reaction (SILAR) to vary the thickness of the CdS shell from 0.5 nm to 2 nm, upon a 2.8 nm diameter CdSe core. Following this, a ligand exchange of the original aliphatic ligands with L- and D-cysteine was carried out, inducing a chiroptical response in these nanostructures. The samples were then characterized using CD, UV-Vis, PL spectroscopy and PL lifetime spectroscopy. It has been found that the induced chiroptical response was inversely proportional to the CdS shell thickness and showed a distinct evolution in signal, while the photoluminescence of our samples showed a direct relationship to shell thickness. In addition, a detailed study of the influence of annealing time on the optical activity and PL quantum yield was performed.
Chapter 4 presents the study of the influence of chiral cysteine molecule concentration and cysteine binding mode on the intensity of QD CD signal. It was revealed that initially, by increasing the cysteine concentration, the QD CD intensity increased, but after reaching a certain critical point, it started to reduce. Remarkably, the intensity of CD signal varied by almost 10 times. NMR and FTIR analysis as well as DFT calculations showed that at low concentrations cysteine bound to QD surface with all three functional groups, while at high concentrations it coordinated only by SH and NH2 groups. These tri- and bidentate forms of bound cysteine appeared to be near stereoisomeric configurations, which can result in general CD signal reduction. In this chapter we also highlight the factors that must be taken into account when designing optically active nanoparticles.
Chapter 5 describes the investigation of enantioselective interactions of fluorescent NPs capped with chiral molecules with A549 cells. These NPs were stabilized with D‐ and L‐cysteine using a ligand exchange technique. It was found that NPs stabilized by opposite ligand enantiomers, had identical PL and UV Vis spectra and mirror‐imaged CD spectra, but displayed different cell accumulation and cytotoxicity: NPs capped with D‐cysteine had greater cytotoxicity than L‐cysteine capped NPs.
Chapter 6 is devoted to the study of the optical properties of complexes of CdSe/ZnS as well as Cd-free ZnSe/ZnS QDs and the photosensitizer chlorin e6 (Ce6), which are widely used for photodynamic therapy. CdSe/ZnS QDs were bound to Ce6 using bovine serum albumin (BSA) as a linker and ZnSe/ZnS QDs created with Ce6 electrostatic complexes. The photodynamic therapy (PDT) test of the electrostatic complexes against the Erlich acsite carcinoma cell culture demonstrated a twofold enhancement of the cancer cell photodynamic destruction compared to that of free chlorin e6 molecules. It was shown that the PDT effect was significantly increased due to two factors: the efficient QD chlorin e6 photoexcitation energy transfer and the improvement of cellular uptake of the photosensitizer in the presence of ZnSe/ZnS QDs.
Finally, chapter 7 presents the conclusions and summarizes main outcomes of this research. It also discusses the future research that would follow on from this work.
In overall, in these studies, we have been able to clearly illustrate the approach and strategies that should be used for designing optimal luminescent optically active QDs for potential biomedical applications. We believe that our findings may lay the groundwork for new approaches to control the biological properties and behaviour of QDs capped with chiral molecules in living cells, including PDT properties of QDs complexes with appropriate photosensitizers (e.g. chlorin e6). | en |
