Dissecting the Factors Affecting the Fluorescence Stability of Quantum Dots in Live Cells

Labeling and imaging of live cells with quantum dots (QDs) has attracted great attention in the biomedical field over the past two decades. Maintenance of the fluorescence of QDs in a biological environment is crucial for performing long-term cell tracking to investigate the proliferation and functional evolution of cells. The cell-penetrating peptide transactivator of transcription (TAT) is a well-studied peptide to efficiently enhance the transmembrane delivery. Here, we used TAT peptide-conjugated QDs (TAT–QDs) as a model system to examine the fluorescence stability of QDs in live cells. By confocal microscopy, we found that TAT–QDs were internalized into cells by endocytosis, and transported into the cytoplasm via the mitochondria, Golgi apparatus, and lysosomes. More importantly, the fluorescence of TAT–QDs in live cells was decreased mainly by cell proliferation, and the low pH value in the lysosomes could also lower the fluorescence intensity of intracellular QDs. Quantitative analysis of the amoun...