Optical characterization of colloidal CdSe quantum dots in endothelial progenitor cells.

We have quantitatively analyzed the confocal spectra of colloidal quantum dots (QDs) in rat endothelial progenitor cells (EPCs) by using Leica TCS SP5 Confocal Microscopy System. Comparison of the confocal spectra of QDs located inside and outside EPCs revealed that the interaction between the QDs and EPCs effectively reduces the radius of the exciton confinement inside the QDs so that the excitonic energy increases and the QD fluorescence peak blueshifts. Furthermore, the EPC environment surrounding the QDs shields the QDs so that the excitation of the QDs inside the cells is relatively weak, whereas the QDs outside the cells can be highly excited. At high excitations, the occupation of the ground excitonic state in the QD outside the cells becomes saturated and high-energy states excited, resulting in a large relaxation energy and a broad fluorescence peak. This permits, in concept, to use QD biomarkers to monitor EPCs by characterizing QD fluorescence spectra.