Upconversion Nanoparticles for Bioimaging and Regenerative Medicine

Abstract

Nanomaterials are proving useful for regenerative medicine in combination with stem cell therapy. Nanoparticles (NPs) can be administrated and targeted to desired tissues or organs and subsequently be used in non-invasive real-time visualization and tracking of cells by means of different imaging techniques, can act as therapeutic agent nanocarriers, and can also serve as scaffolds to guide the growth of new tissue. NPs can be of different chemical nature, such as gold, iron oxide, cadmium selenide, and carbon, and have the potential to be used in regenerative medicine. However, there are still many issues to be solved, such as toxicity, stability, and resident time. Upconversion NPs have relevant properties such as (i) low toxicity, (ii) capability to absorb light in an optical region where absorption in tissues is minimal and penetration is optimal (note they can also be designed to emit in the near-infrared region), and (iii) they can be used in multiplexing and multimodal imaging. An overview on the potentiality of upconversion materials in regenerative medicine is given.

Keywords: NIR excitation; cell behavior regulation; multi-wavelength/multimodal bioimaging; non-toxic nanoparticles; transparency; upconverted (UV–VIS–NIR) emission.

Figure 1

Overview of UCNPs properties and reasons to apply them in regenerative medicine.

Figure 2

(A) Schematic illustration of the utilization of SP-UCNP as a NIR-triggered photoswitch for non-invasive and reversible control of cell adhesion/detachment by merely altering the power density of a single-wavelength 980-nm laser. Reprinted with permission from Li et al. (2015). Copyright (2015) American Chemical Society (Li et al., 2015). (B) Top: UCL image of a C56BL/6 mouse subcutaneously injected with various numbers of UCNPs labeled DCs (≈50–50,000). Middle: labeled DCs were injected into the rig; strong UCL signals from the draining lymph node were seen under in vivo UCL imaging. Bottom: ex vivo imaging of popliteal lymph nodes (white circles) before (top) and after (bottom) being dissected from the mouse. (C) Immunofluorescence images of the lymph nodes dissected from the mouse injected with UPP@OVA-labeled DCs. T: T-cell zone (Thy1.2⁺). B: B-cell zone (B220⁺). Scale bar = 20 μm. Arrows point to UCL signals from labeled DCs. Adapted with permission from Xiang et al. (2015). Copyright (2015) American Chemical Society (Xiang et al., 2015).