Highly Sensitive Naphthalimide-Based Fluorescence Polarization Probe for Detecting Cancer Cells

Fluorescence polarization (FP)-based signal is a self-referencing fluorescence signal, and it is less dependent on dye concentration and environmental interferences, which makes FP measurement an attractive alternative sensing technology to fluorescence intensity-based detection. However, most of the fluorescence polarization probes were constructed by introducing fluorescein, rhodamine, and cyanine dyes, which have relatively shorter excited-state lifetimes compared with BODIPY and naphthalimide dyes. Herein, a first naphthalimide based fluorescence polarization probe (<b>BIO</b>) was designed and synthesized for selective and direct detection of cancer cells. The relatively longer excited-state lifetimes and high photostability of naphthalimide makes <b>BIO</b> more sensitive and accuracy in quantitative determination of HeLa cells in homogeneous solution without cell lysis and further separation steps. The detection limit of <b>BIO</b> for HeLa cells was about 85 cells mL^–1, the linear range was from 2.5 × 10² cells mL^–1 to 1 × 10⁶ cells mL^–1 and the response time is no more than 25 min. Moreover, due to the relatively high photostability of naphthalimide, <b>BIO</b> was particularly suitable for live cell imaging under continuous irradiation with confocal microscopy, and the specific interaction of <b>BIO</b> with CD44-overexpressing cell lines was clearly visualized. Importantly, this <b>BIO</b> based sensing platform offers a direct and real-time tool for cancer cell diagnosis when complemented with the use of naphthalimide-based fluorescence polarization probe