Targeted Bioimaging of Cancer Cells Using Free Folic Acid-Sensitive Molybdenum Disulfide Quantum Dots through Fluorescence "Turn-Off".

In the present study, a proficient way for targeted bioimaging of folate receptor (FR)-positive cancer cells using free folic acid (FA)- and MoS 2 QD-based nanoprobes is discussed along with its advantages over the preparation of orthodox direct FA-nanoprobe bioconjugates for the imaging. The water-soluble MoS 2 QDs of size 4-5 nm with cysteine functionalization are synthesized by a simplistic bottom-up hydrothermal method. The as-prepared MoS 2 QDs exhibit the blue emission with the highest emission intensity at 444 nm upon excitation of 370 nm. The MoS 2 QDs are too sensitive toward FA to produce an effective and stable nanofiber structure through supramolecular interaction, which demonstrates ∼97% quenching of fluorescence. Moreover, the high selectivity and sensitivity of MoS 2 QDs toward FA make the MoS 2 QD-based nanoprobe an appropriate candidate for FA-targeted "turn-off" imaging probes for in vivo study of FA-pretreated FR-overexpressed cancer cells. It is obvious from the confocal microscopy images that the FA-pretreated B16F10 cancer cells show higher population of dimmed fluorescence compared to untreated cancer cells and HEK-293 normal cells. The flow cytometry study quantitatively reveals the significant difference of the geometric mean of fluorescence between FA-pretreated and untreated B16F10 cancer cells. Hence, these MoS 2 QD-based nanoprobes can be applied as potential nanoprobes for the prediagnosis of cancer through targeted bioimaging.