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 amount of QDs in the extracellular region and whole cells indicated that the exocytosis was not the primary cause of fluorescence decay of intracellular QDs. This work facilitates a better understanding of the fluorescence stability of QDs for cell imaging and long-term tracking in live cells. Also, it provides insights into the utility of TAT for transmembrane transportation, and the preparation and modification of QDs for cell imaging and tracking.

中文翻译：

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剖析影响活细胞量子点荧光稳定性的因素

在过去的二十年中，使用量子点（QD）对活细胞进行标记和成像已在生物医学领域引起了极大的关注。在生物环境中维持QDs的荧光对于执行长期细胞追踪以研究细胞的增殖和功能进化至关重要。穿透细胞的转录肽反式激活因子（TAT）是一种经过充分研究的肽，可有效增强跨膜递送。在这里，我们使用TAT肽共轭QD（TAT–QDs）作为模型系统来检查活细胞中QD的荧光稳定性。通过共聚焦显微镜，我们发现TAT-QDs通过内吞作用被内化到细胞中，并通过线粒体，高尔基体和溶酶体转运到细胞质中。更重要的是，活细胞中TAT-QDs的荧光主要通过细胞增殖而降低，而溶酶体的低pH值也可能降低细胞内QDs的荧光强度。定量分析细胞外区域和全细胞中QD的数量表明，胞吐作用不是细胞内QDs荧光衰减的主要原因。这项工作有助于更好地了解QD的荧光稳定性，以用于活细胞成像和长期跟踪。此外，它还提供了有关TAT在跨膜运输中的用途以及用于细胞成像和跟踪的QD的制备和修饰的见解。定量分析细胞外区域和全细胞中QD的数量表明，胞吐作用不是细胞内QDs荧光衰减的主要原因。这项工作有助于更好地了解QD的荧光稳定性，以用于活细胞成像和长期跟踪。此外，它还提供了有关TAT在跨膜运输中的用途以及用于细胞成像和跟踪的QD的制备和修饰的见解。定量分析细胞外区域和全细胞中QD的数量表明，胞吐作用不是细胞内QDs荧光衰减的主要原因。这项工作有助于更好地了解QD的荧光稳定性，以用于活细胞成像和长期跟踪。此外，它还提供了有关TAT在跨膜运输中的用途以及用于细胞成像和跟踪的QD的制备和修饰的见解。