Cytotoxicity Evaluation of Photosensitizer-Conjugated Hexagonal Upconverting Nanoparticles

In this report, we synthesized hexagonal NaYF4:Yb,Er upconverting nanoparticles (UCNPs) of 171 nm in size with a narrow particle size distribution. To address their colloidal stability in aqueous media and to incorporate a photosensitizer that can produce reactive singlet oxygen (O-1(2)) to kill tumor cells, UCNPs were conjugated with 6-bromohexanoic acid-functionalized Rose Bengal (RB) and coated with PEG-alendronate (PEG-Ale). The particles were thoroughly characterized by transmission electron microscopy, dynamic light scattering, ATR FTIR, X-ray photoelectron spectroscopy, thermogravimetric analysis, and spectrofluorometry, and O-1(2) formation was detected using a 9,10-diphenylanthracene spectrophotometric probe. Cytotoxicity determination on rat mesenchymal stem cells by using the MTT assay showed that neutralization of the large positive surface charge of neat UCNPs with PEG-Ale and the bound RB sensitizer significantly reduced the concentration-dependent cytotoxicity. The presented strategy shows great potential for the use of these particles as a novel agent for the photodynamic therapy of tumors.

Automated summary

In this study, hexagonal NaYF4:Yb,Er upconverting nanoparticles (UCNPs) of 171 nm in size with a narrow particle size distribution were successfully synthesized. To improve their colloidal stability in aqueous media and incorporate a photosensitizer for producing reactive singlet oxygen (O-1(2)) to kill tumor cells, UCNPs were conjugated with 6-bromohexanoic acid-functionalized Rose Bengal (RB) and coated with PEG-alendronate (PEG-Ale). Characterization using various techniques confirmed the successful synthesis and O-1(2) formation. Cytotoxicity tests on rat mesenchymal stem cells showed reduced concentration-dependent cytotoxicity after neutralization of the positive surface charge of UCNPs and incorporation of the RB sensitizer.