Quantum dot biomarkers for tracking endothelial progenitor cells and activated endothelium

Sammanfattning: The development of new visualization techniques is essential in the field of bioimaging to gain deeper knowledge about various medical and biological events at the cellular and molecular levels. Quantum dots (QDs) are semiconductor nanocrystals which are opening new perspectives in biotechnology due to their powerful optical properties and high stability.  Utilization of QDs instead of commonly used organic dyes in labeling techniques adds several advantages, such as longer signal observation time of the biological samples; convenient multicolor labeling; deep tissue and organ tracking. Furthermore, more information can be obtained about the environment where QDs are located by characterizing the optical behavior of the QDs.In this thesis work carboxyl coated QDs were used to label endothelial progenitor cells (EPCs). EPCs play an important role in cardiovascular diseases and the repair of the damaged endothelium, therefore an efficient in vivo tracking method is essential to understand the therapeutic potential of these cells. Our findings show an effective, cytoplasmic labeling of EPCs. Cell viability assay shows that QDs are not toxic to the cells in the concentration and incubation time tested in the study and QDs does not change the cell functions.Furthermore commercially available QDs were functionalized with VCAM-1 binding peptide (VCAM-1BP) to specifically detect activated endothelial cells and activated endothelial wall in the aorta. Endothelial wall of the arteries are activated with VCAM-1 in the early stages of atherosclerosis, therefore early detection of this chronic disease may be performed with VCAM-1BP functionalized QDs. We found that VCAM-1BP functionalized QDs were able to detect the activated endothelium specifically.The optical behavior of the QDs in different conditions and bio-systems were also characterized. It was found that several circumstances like different coating ligands can modify the fluorescence of the QDs. We observed that QD fluorescence intensity changes with different concentrations of Na+ and K+. We also found that significant blue-shift in QD peak emission occurs when QDs are internalized by cells and when functionalized QDs interact with cell surface molecule.This thesis work provides efficient labeling techniques for cells and tissues with QDs and important knowledge about the optical behavior of QDs in bio-systems. These results give further perspectives to the future application of QD biomarkers as tracking agent and optical sensors for the different environmental changes in bio-systems.