Rose Bengal-Modified Upconverting Nanoparticles: Synthesis, Characterization, and Biological Evaluation

Abstract

High-quality upconverting NaYF₄:Yb³⁺,Er³⁺ nanoparticles (UCNPs; 26 nm in diameter) based on lanthanides were synthesized by a high-temperature coprecipitation method. The particles were modified by bisphosphonate-terminated poly(ethylene glycol) (PEG) and Rose Bengal (RB) photosensitizer. The particles were thoroughly characterized using transmission electron microscopy, dynamic light scattering, thermogravimetric analysis, FTIR, and X-ray photoelectron and upconversion luminescence spectroscopy in terms of morphology, hydrodynamic size, composition, and energy transfer to the photosensitizer. Moreover, the singlet oxygen generation from RB-containing UCNPs was investigated using 9,10-diphenylanthracene probe under 980 nm excitation. The cytotoxicity of UCNPs before and after conjugation with RB was evaluated on highly sensitive rat mesenchymal stem cells (rMSCs) and significant differences were found. Correspondingly, consi-derable variations in viability were revealed between the irradiated and non-irradiated rat glioma cell line (C6) exposed to RB-conjugated UCNPs. While the viability of rMSCs was not affected by the presence of UCNPs themselves, the cancer C6 cells were killed after the irradiation at 980 nm due to the reactive oxygen species (ROS) production, thus suggesting the potential of RB-conjugated PEG-modified UCNPs for applications in photodynamic therapy of cancer.

Keywords: Rose Bengal; cytotoxicity; nanoparticles; photodynamic therapy; reactive oxygen species; upconverting.

Figure 1

(a) Preparation of Rose Bengal-ethylphosphonic acid (RB-PH); (b) modification of UCNPs with PEG-Ale and RB-PH.

Figure 2

TEM micrograph of (a) UCNP@OA; (b) UCNP@Ale-PEG; (c) UCNP@RB-PH/Ale-PEG nanoparticles.

Figure 3

(a) Intensity of luminescence of UCNP@OA particles after excitation at 980 nm; (b) TEM micrographs of particles prepared at different reaction times (15, 30, 45, 60, 75, and 90 min)/300 °C.

Figure 4

Comparison of high-resolution XPS spectra of initial UCNP@OA (black), UCNP@Ale-PEG (magenta), and UCNP@RB-PH/Ale-PEG (royal) in the region of (a) P 2p, Y 3d, Er 4d, Yb 4d, P 2s, Cl 2p and (b) C 1s (red, fitted data; blue, individual contributions of functional groups on the UNCP surface).

Figure 5

(a) Thermogravimetric analysis; (b) FTIR; (c) luminescence spectra of surface-modified UCNPs excited at 980 nm.

Figure 6

UV-Vis spectra of (a) RB-PH excited at 525–535 nm and (b) UCNP@RB-PH/Ale-PEG excited at 980 nm document time-dependent decrease of DPA absorbance due to ¹O₂ generation (see the arrow); (b) black dashed line is for UCNP@OA particles. Each curve was measured after 10 min delay.

Figure 7

Cytotoxicity of bare UCNPs (green) and UCNP@RB-PH/Ale-PEG particles (blue) against rMSCs after 24 h of incubation using MTT cell viability assay. Error bars represent standard error means (S.E.M.) calculated from at least three different experiments performed in triplicates; ** p < 0.01 (two-tailed unpaired Student’s t-test).

Figure 8

Viability of C6 glioma cells in the presence of UCNP@RB-PH/Ale-PEG particles (1 mg/mL) without irradiation (control; blue) and after 10 min of irradiation at 980 nm in the absence (green) and presence of particles (red); ** p < 0.01 (Student’s t-test).