Folic acid-modified fluorescent dye-protein nanoparticles for the targeted tumor cell imaging

Serum albumin has a wide range of applications in biochemical experiments and pharmaceutical field. We found that a cyanine dye, dimethylindole red (Dir), could selectively interact with bovine serum albumin (BSA). Dir exhibited very weak red fluorescence, while the fluorescence intensity at 630 nm was enhanced up to 130-fold upon noncovalently interacting with 30 µM BSA. Besides, Dir showed a highly selective response to BSA over human serum albumin (HSA). For the detection of BSA, a limit of detection as low as 23 nM was obtained. Then biocompatible Dir-BSA nanoparticles were prepared by the desolvation technique. The Dir-BSA nanoparticles possess excellent fluorescence properties with a quantum yield of 32%. Furthermore, folic acid as a targeting group was conjugated to Dir-BSA nanoparticles and these nanoparticles were characterized by TEM and laser particle analyzer, etc. Folic acid-modified Dir-BSA nanoparticles were successfully used for tumor cell-targeted imaging.