Upconverting organic dye doped core-shell nano-composites for dual-modality NIR imaging and photo-thermal therapy

Abstract

Nanotechnology approaches offer the potential for creating new optical imaging agents with unique properties that enable uses such as combined molecular imaging and photo-thermal therapy. Ideal preparations should fluoresce in the near-infrared (NIR) region to ensure maximal tissue penetration depth along with minimal scattering and light absorption. Due to their unique photophysical properties, upconverting ceramics such as NaYF4:Er3+,Yb3+ nanoparticles have become promising optical materials for biological imaging. In this work, the design and synthesis of NaYF4:Er3+,Yb3+@SiO2 core-shell nano-composites, which contain highly absorbing NIR carbocyanine dyes in their outer silica shell, are described. These materials combine optical emission (from the upconverting core nanoparticle) with strong NIR absorption (from the carbocyanine dyes incorporated into the shell) to enable both optical imaging and photo-thermal treatment, respectively. Ultimately, this hybrid composite nanomaterial approach imparts the ability to both visualize, via upconversion imaging, and treat, via photo-thermal heating, using two distinct optical channels. Proof-of-principle in vitro experiments are presented to demonstrate the combined imaging and photo-thermal properties of this new functional nano-composite.

Keywords: Cell imaging; Core-shell; Dye; Nano-composites; Photo-thermal therapy; Up-conversion..

Figure A

(Scheme 1) Application of UNP@SiO₂/Dye nano-composites (Blue dots and Green dots) for optical imaging and photo-thermal therapy (cell disruption).

Figure 1

(A): Synthetic scheme and (B-D): TEM images (B, upconverting nanoparticles (UNPs); C, UNP@SiO₂ core/shell nanoparticles; D, UNP@SiO₂/Dye nano-composites) of the nanoparticles.

Figure 2

Optical and heating properties of UNP@SiO₂/Dye nano-composites. (A): Absorbance spectrum of UNP@SiO₂/Dye; (B): Up-conversion luminescence spectrum of UNP@SiO₂/Dye; (C): Temperature change (Delta temperature) of a 2.0 mg/mL aqueous suspension of UNP@SiO₂/Dye and control solution upon irradiation with a 750-nm laser (2.5 W/cm²).

Figure 3

Cell images of macrophages (RAW). (A): DAPI nuclear stain; (B) Upconversion emission; (C): Composite of A and B; and (D): White light.

Figure 4

Cell viability of macrophages (RAW) using UNP@SiO₂/Dye nano-composites(Irradiation time: 3 minutes; 1 W/cm² at 750 or 980 nm) Control cells were incubated with the nano-composite but not subjected to light treatment.