Fluorescent small Au nanodots prepared from large Ag nanoparticles for targeting and imaging cancer cells

Developing an approach for targeting and detecting cancer cells has long been a challenge. Herein, the folic acid (FA) conjugated gold nanodots (Au NDs) are designed for specifically targeting and imaging folate receptor (FR) positive cancerous cells. Fluorescent small Au NDs were synthesized using stable Ag NPs with size above 50 nm and GSH as capping agent. This method solves the problems of low stability and difficulty in purification of small Ag NDs as templates. The resulting Au NDs display pink fluorescence with an emission peak at 582 nm. As-prepared Au NDs provide tunable fluorescence with a significant red shift (similar to 60 nm) with increase in the amount of GSH. In addition, GSH acts as a protecting layer, which could provide original functional groups (thiol, carboxyl and amine) and make Au NDs exhibit outstanding properties such as dispersibility in water, high stability, good biocompatibility and surface bioactivity. These characteristics make them suitable for further conjugation with FA. FA-conjugated Au NDs show the specific target HeLa cancer cells compared with 293T normal cells. These properties provide Au NDs with potential applications in distinguishing FR-positive cancer cells from normal cells.