Amplifying the red-emission of upconverting nanoparticles for biocompatible clinically used prodrug-induced photodynamic therapy

Abstract

A class of biocompatible upconverting nanoparticles (UCNPs) with largely amplified red-emissions was developed. The optimal UCNP shows a high absolute upconversion quantum yield of 3.2% in red-emission, which is 15-fold stronger than the known optimal β-phase core/shell UCNPs. When conjugated to aminolevulinic acid, a clinically used photodynamic therapy (PDT) prodrug, significant PDT effect in tumor was demonstrated in a deep-tissue (>1.2 cm) setting in vivo at a biocompatible laser power density. Furthermore, we show that our UCNP-PDT system with NIR irradiation outperforms clinically used red light irradiation in a deep tumor setting in vivo. This study marks a major step forward in photodynamic therapy utilizing UCNPs to effectively access deep-set tumors. It also provides an opportunity for the wide application of upconverting red radiation in photonics and biophotonics.

Keywords: nanoparticles; photodynamic therapy; prodrug; red-emission; upconverting.

Figure 1

Emission spectra (a) under CW 980 nm, 1 W/cm² excitation of α-NaYF₄:Yb,Er@CaF₂ UCNPs with different Yb-levels. Integrated counts of red-emission (b) and photographs (inset) of α-NaYF₄:Yb,Er@CaF₂ UCNPs with different Yb-levels.

Figure 2

Characterization of hydrophilic UCNPs: TEM images of PAA–UCNPs (a), Hyd–UCNPs (b), and ALA–UCNPs (c). Full FTIR spectra (d) and partial detailed spectra (e) of PAA–UCNPs, Hyd–UCNPs, and ALA–UCNPs.

Figure 3

HeLa cell viability exposed to ALA–UCNPs (100 μg/mL), Hyd–UCNPs (100 μg/mL), free ALA (100 μg/mL), and nothing (growth control) and irradiated with CW 980 nm light at 0.5 W/cm² power density.

Figure 4

HeLa cell viability exposed to α-NaYF₄:Yb(80%),Er(2%)@CaF₂ and β-NaYF₄:Yb(20%),Er(2%)@β-NaYF₄ ALA–UCNPs (100 μg/mL) and α-NaYF₄:Yb(80%),Er(2%)@CaF₂ and β-NaYF₄:Yb(20%),Er(2%)@β-NaYF₄ Hyd–UCNPs (100 μg/mL) and irradiated with CW 980 nm light at 0.5 W/cm² power density.

Figure 5

Singlet oxygen production detected by fluorescence of DCFDA in HeLa cells exposed to 100 μg/mL of ALA–UCNPs and irradiated with 0 (a), 5 (b), and 10 min (c) of CW 980 nm light. Singlet oxygen production detected by fluorescence of DCFDA in HeLa cells exposed to 100 μg/mL of Hyd–UCNPs and irradiated with 0 (d), 5 (e), and 10 min (f) of CW 980 nm light.

Figure 6

Singlet oxygen quantified by DCFDA fluorescence in HeLa cells exposed to 100 μg/mL of ALA UCNPs, Hyd–UCNPs, ALA, and nothing (growth control).

Figure 7

Photograph of the setup of simulated deep tumor conditions in an in vitro MTT assay (a). HeLa cell viability exposed to α-NaYF4:Yb(80%),Er(2%)@CaF₂ and β-NaYF4:Yb(20%),Er(2%)@β-NaYF4 ALA–UCNPs (100 μg/mL) and α-NaYF4:Yb(80%),Er(2%)@CaF2 and β-NaYF4:Yb(20%),Er(2%)@β-NaYF4 Hyd–UCNPs (100 μg/mL) and irradiated with CW 980 nm light at 0.5 W/cm² power density for 40 min with 0, 6, and 12 mm pork tissue on top of the cells (b).

Figure 8

In vivo volume of tumors exposed to various controls and ALA–UCNPs with red and near-infrared irradiation (0.5 W/cm²) in simulated deep tumors. Legend: gray square, untreated tumors serving as growth controls; light gray square, tumors exposed to ALA–UCNPs and no irradiation; black square, tumors simultaneously exposed to red and NIR light both at 0.5 W/cm², but no ALA–UCNPs; blue triangle, tumors exposed to ALA–UCNPs and clinically used red light; navy blue triangle, tumors 6 mm deep exposed to ALA–UCNPs and clinically used red light; light blue triangle, tumors 12 mm deep exposed to ALA–UCNPs and clinically used red light; red hexagon, tumors exposed to ALA–UCNPs and deep-penetrating 980 nm light; magenta hexagon, tumors 6 mm deep exposed to ALA–UCNPs and deep-penetrating 980 nm light; brown hexagon, tumors 12 mm deep exposed to ALA–UCNPs and deep-penetrating 980 nm light. Statistical significance was determined from one-way t tests; significance (*) was based on p < 0.05 and p > 0.05 for not significant (**) pairs.