Photoluminescent nanoplatforms in biomedical applications

Figures & data

Figure 1. (A) Cartoon, photograph, and PL spectra illustrating progressive color changes of CdSe/ZnS with increasing nanocrystal size. (B) Qualitative changes in QD energy levels with increasing nanocrystal size. Band gap energies, E_g, were estimated from PL spectra. Conduction (CB) and valence (VB) bands of bulk CdSe are shown for comparison. The energy scale is expanded as 10E for clarity. Reprinted with permission from [19]. Copyright © 2011, American Chemical Society.

Figure 2. Upconversion emission (λ_exc = 980 nm) for (A) NaYF₄:Er³⁺/Yb³⁺ (2/18 mol%), (B) NaYF₄:Tm³⁺/Yb³⁺ (0.2/20 mol%), (C) NaYF₄:Er³⁺/Yb³⁺ (2/25–60 mol%), and (D) NaYF₄:Er³⁺/Tm³⁺/Yb³⁺ (0.2–1.5/0.2/20 mol%) nanoparticles in ethanol (10 mM). Photos of the emission of colloidal solutions of (E) NaYF₄:Tm³⁺/Yb³⁺ (0.2/20 mol%), (F–J) NaYF₄:Er³⁺/Tm³⁺/Yb³⁺ (0.2–1.5/0.2/20 mol%), and (K–N) NaYF₄:Er³⁺/Yb³⁺ (2/25–60 mol%). Camera exposure times of 3.2 s for (E–L) and 10 s for (M) and (N). Reprinted with permission from [34]. Copyright © 2008, American Chemical Society.

Figure 3. (A) In the ESA mechanism, an incoming pump photon of a wavelength resonant with the E₁ − G energy gap excites ion X from G to E₁. A second incoming pump photon promotes the ion from E₁ to E₂, followed by a visible emission and relaxation of the ion to the G state. (B) In the ETU mechanism, an incoming pump photon promotes both donor ions Y (ion with higher absorption cross section) to the intermediate excited state E₁. A non-radiative energy transfer occurs from the donor ion Y to the acceptor ion X that results in the promotion of the latter to the E₁. A second energy transfer promotes the acceptor to the excited state E₂. Finally, the donor ions relax back to their ground state, while the acceptor ion undergoes a radiative decay returning to the ground state. Reprinted with permission from [37]. Copyright © 2015, John Wiley and Sons.

Figure 4. In vivo real-time visualization of tumor-induced angiogenesis. NIR-II fluorescence images of the 4T1 mammary tumor-bearing mouse. Fluorescence images were acquired after 30 min post-tail vein injection of PEGylated Ag₂S QDs; (A) Color photo of U87MG tumor-bearing mouse. (B) Amplified fluorescent image of the selected region in (A). (C) In vivo fluorescence images of CdSe@ZnS QDs, ICG (NIR-I), and Ag₂S QDs (NIR-II) in nude mice. CdSe@ZnS QDs, ICG, and Ag₂S QDs were injected intravenously into mice and fluorescence images were taken after i.v. injection for 5 min under excitation at 455, 704, and 808 nm, respectively. The green-yellow signal of the mouse injected with CdSe@ZnS QDs indicates the strong autofluorescence of tissues in the visible emission window. The red signal concentrated in the liver of the mouse injected with ICG indicates the short blood circulation half-time. The red signal widely distributed in the whole body of mouse injected with Ag₂S QDs indicates the long blood circulation half-time. (D) The PL spectra of CdSe@ZnS QDs, ICG, and Ag₂S QDs. Reprinted with permission from [118]. Copyright © 2014, Elsevier.

Figure 5. Comparison of imaging sensitivities between UCNPs and QDs: (A) white light image of a mouse subcutaneously injected with various concentrations of NaYF₄:Er/Yb UCNPs. (B) in vivo UCL image of the injected mouse. (C) and (E) white light images of mice subcutaneously injected with QDs; spectrally resolved fluorescence images of QD545 injected mouse (D) and QD 625 injected mouse (F) 625 injected mouse (red and green colors represent QD fluorescence and autofluorescence, respectively). Reprinted with permission from [121]. Copyright © 2010, Tsinghua University Press and Springer-Verlag Berlin Heidelberg.

Figure 6. In vivo lymphatic imaging using PoP-UCNPs in mice 1 h post-injection. Accumulation of PoP-UCNPs in the first draining lymph node is indicated with yellow arrows. (A) Traditional FL and (B) UC images with the injection site cropped out of frame. (C) Full anatomy PET, (D) merged PET/CT, and (E) CL images. (F) PA images before and (G) after injection show endogenous PA blood signal compared to the contrast enhancement that allowed visualization of the previously undetected lymph node. Reprinted with permission from [152]. Copyright © 2015, John Wiley and Sons.

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