Department of Pathology, The Ohio State University, Columbus, Ohio, USA.
Chem Res Toxicol. 2011 Dec 19;24(12):2176-88. doi: 10.1021/tx2003195. Epub 2011 Nov 30.
Quantum dots (QDs) are semiconductor nanocrystals that have found use in bioimaging, cell tracking, and drug delivery. This article compares the cytotoxicity and cellular interactions of positively and negatively charged CdSe/CdS/ZnS QDs prepared by a microwave method using a murine alveolar macrophage-like cell culture model. Keeping the core semiconductor the same, QD charge was varied by altering the surface capping molecule; negatively charged QDs were formed with mercaptopropionic acid (MPA-QDs) and positively charged QDs with thiocholine (THIO-QDs). The size and charge of these two QDs were investigated in three types of media (RPMI, RPMI + FBS, and X-VIVO serum-free media) relevant for the biological studies. MPA-QDs were found to have negative zeta potential in RPMI, RPMI + FBS, and serum-free media and had sizes ranging from 8 to 54 nm. THIO-QDs suspended in RPMI alone were <62 nm in size, while large aggregates (greater than 1000 nm) formed when these QDs were suspended in RPMI + FBS and serum-free media. THIO-QDs retained positive zeta potential in RPMI and were found to have a negative zeta potential in RPMI + FBS and nearly neutral zeta potential in serum-free media. In a cell culture model, both MPA-QDs and THIO-QDs caused comparable levels of apoptosis and necrosis. Both QDs induced significant tumor necrosis factor-alpha (TNF-α) secretion only at high concentrations (>250 nM). Both types of QDs were internalized via clathrin-dependent endocytosis. Using real-time, live cell imaging, we found that MPA-QDs interact with the cell surface within minutes and progress through the endocytic pathway to the lysosomes upon internalization. With the THIO-QDs, the internalization process was slower, but the pathways could not be mapped because of spectroscopic interference caused by QD aggregates. Finally, MPA-QDs were found to associate with cell surface scavenger receptors, while the THIO-QDs did not. This study indicates that the surface charge and aggregation characteristics of QDs change drastically in biological culture conditions and, in turn, influence nanoparticle and cellular interactions.
量子点 (QDs) 是一种半导体纳米晶体，已在生物成像、细胞跟踪和药物输送中得到应用。本文比较了通过微波法制备的带正电荷和带负电荷的 CdSe/CdS/ZnS QD 的细胞毒性和细胞相互作用，该方法使用了鼠肺泡巨噬细胞样细胞培养模型。通过改变表面封端分子保持核心半导体相同，改变 QD 电荷；带负电荷的 QD 由巯基丙酸 (MPA-QD) 形成，带正电荷的 QD 由硫代胆碱 (THIO-QD) 形成。这两种 QD 的大小和电荷在三种与生物学研究相关的介质（RPMI、RPMI+FBS 和 X-VIVO 无血清培养基）中进行了研究。在 RPMI、RPMI+FBS 和无血清培养基中，MPA-QD 具有负的 ζ 电位，其大小范围为 8 至 54nm。单独悬浮在 RPMI 中的 THIO-QD 尺寸小于 62nm，而当这些 QD 悬浮在 RPMI+FBS 和无血清培养基中时，会形成大的聚集体（大于 1000nm）。THIO-QD 在 RPMI 中保留正的 ζ 电位，在 RPMI+FBS 中呈负 ζ 电位，在无血清培养基中几乎呈中性 ζ 电位。在细胞培养模型中，MPA-QD 和 THIO-QD 均引起相当水平的细胞凋亡和坏死。两种 QD 仅在高浓度（大于 250nM）时才会引起显著的肿瘤坏死因子-α (TNF-α) 分泌。两种 QD 均通过网格蛋白依赖性内吞作用被内化。使用实时、活细胞成像，我们发现 MPA-QD 在几分钟内与细胞表面相互作用，并在内化后通过内吞途径进入溶酶体。对于 THIO-QD，内化过程较慢，但由于 QD 聚集体引起的光谱干扰，无法对途径进行映射。最后，发现 MPA-QD 与细胞表面的清道夫受体结合，而 THIO-QD 则不结合。本研究表明，QD 的表面电荷和聚集特性在生物培养条件下发生剧烈变化，进而影响纳米颗粒和细胞相互作用。
