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.