叶酸（FA）是一种配基，因其与叶酸受体（FR）的强结合而闻名。这种特定相互作用的强度导致产生大量的肿瘤靶向纳米药物传递系统。然而，根据癌细胞类型选择适当的FA靶向纳米药物以达到高效应用是至关重要的。了解药物如何通过细胞膜运输并在细胞内递送非常重要，以筛选适用于不同器官癌变的理想靶向纳米药物。在这里，利用原子力显微镜（AFM）的力追踪技术，实时监测了FA-聚酰胺胺-多西环素（FA-PAMAM-DOX）进入不同肿瘤细胞（HeLa和A549）和正常细胞（Vero）的动态过程。分析了FR高过度表达水平（HeLa）和FR低过度表达水平（A549）的肿瘤细胞中FA-PAMAM-DOX的细胞膜转运效果，其显著高于正常细胞（Vero），尤其是对于HeLa细胞。随后，利用荧光成像和基于AFM的纳米压痕技术测量了FA-PAMAM-DOX在不同细胞系中的细胞内输送效率。本报告将有助于发现纳米药物的细胞运输机制，并筛选出适用于不同类型肿瘤的最佳治疗纳米药物。

Folic acid (FA) is a ligand that has been renowned for its strong binding to FA receptor (FR), and the robustness of the specific interaction has led to the generation of multitudinous tumor-targeted nano-drug delivery systems. However, selecting the appropriate FA targeted nano-drugs according to types of cancerous cells to achieve a high effect is critical. Understanding of how the drug is transported through the cell membrane and is delivered intracellularly is very important in screening ideal targeted nano-drugs for cancerous changes in different organs. Herein, by using a force tracing technique based on atomic force microscopy (AFM), the dynamic process of FA-polyamidoamine-Doxorubicin (FA-PAMAM-DOX) entry into different tumor cells (HeLa and A549) and normal cells (Vero) was monitored in real time. The cell membrane transport efficacy of FA-PAMAM-DOX in tumor cells with an FR high overexpression level (HeLa) and FR low overexpression level (A549) is analyzed, which is significantly higher than that in normal cells (Vero), especially for HeLa cells. Subsequently, the intracellular delivery efficiency of FA-PAMAM-DOX in different cell lines was measured by using fluorescence imaging and AFM-based nanoindentation techniques. This report will help to discover the cellular transport mechanism of nano-drugs and screen out optimal therapeutic nano-drugs for different types of tumors.