Low Toxicity, High Resolution, and Red Tissue Imaging in the Vivo of Yb/Tm/GZO@SiO2 Core-Shell Upconversion Nanoparticles

Abstract

Lanthanide-doped upconversion nanoparticles (UCNPs) have attracted great attention in bioimaging applications. However, the stability and resolution of bioimaging based on UCNPs should be further improved. Herein, we synthesized SiO₂-coated Ga(III)-doped ZnO (GZO) with lanthanide ion Yb(III) and Tm(III) (Yb/Tm/GZO@SiO₂) UCNPs, which realized red fluorescence imaging in heart tissue. With increasing injection concentrations of Yb/Tm/GZO@SiO₂ (1-10 mg/kg), the red fluorescence imaging intensity of heart tissue gradually increased. Moreover, the experimental results of toxicity in vitro and histological assessments of representative organs in vivo were studied, indicating that Yb/Tm/GZO@SiO₂ UCNPs had low biological toxicity. These results proved that Yb/Tm/GZO@SiO₂ can be used as a probe for fluorescence imaging in vivo.

Scheme 1. Schematic Representation of the Imaging Mechanism of the Live Cell with Injection of UCNPs

Figure 1

(A) SEM and TEM characterization of Yb/Tm/GZO (Ga: 10 mol %, Yb: 7 mol %, Tm: 0.5 mol % mol %) UCNPs. (B) Synthesis process of the Yb/Tm/GZO@SiO₂ core/shell structure. (C) TEM images of Yb/Tm/GZO@SiO₂ with different contents of TEOS from 0.36 to 0.90 mL. (D) Size distribution of Yb/Tm/GZO@SiO₂ with 0.60 mL of TEOS by gauss fitting.

Figure 2

(A) X-ray diffraction spectra of Yb/Tm/GZO and Yb/Ym/GZO@SiO₂ nanoparticles. (B) FTIR spectra of Yb/Tm/GZO and Yb/Ym/GZO@SiO₂ nanoparticles. (C) Ultraviolet–visible (UV–vis) absorption spectra of Yb/Tm/GZO and Yb/Tm/GZO@SiO₂ nanoparticles. (D) Upconversion luminescence spectra of Yb/Tm/GZO@SiO₂ with different TEOS contents. (E) Decay lifetime for the 650 nm band for Yb/Tm/GZO@SiO₂ with different TEOS concentrations from 0 to 0.9 mL. (F) UCL intensities of Yb/Tm/GZO@SiO₂ (TEOS: 0.6 mL) with different assembly times from 0 to 25 days at room temperature; the inset shows the digital photographs of Yb/Tm/GZO@SiO₂ (TEOS: 0.6 mL) with different assembly times from 0 to 25 days.

Figure 3

(A) Scheme of the proposed nanostructure. (B) Corresponding log (UC intensity)–log (excitation power) curve of Yb/Tm/GZO@SiO₂ nanoparticles. (C) Proposed energy transfer mechanism of Yb/Tm/GZO@SiO₂ under 980 nm excitation.

Figure 4

(A) 7702 cell viability after incubating with different charged Yb/Tm/GZO@SiO₂ concentrations ranging from 100 to 800 μg/mL for 24, 48, and 72 h. (B) HpG2 cell viability after incubating with different charged Yb/Tm/GZO@SiO₂ concentrations ranging from 100 to 800 μg/mL for 24, 48, and 72 h.

Figure 5

Serum levels after tail vein injection with Yb/Tm/GZO@SiO₂ with different concentrations (1–10 mg/kg) at 24 h and 7 days. (A) albumin (ALB); (B) alkaline phosphatase (ALP); (C) alanine transaminase (ALT); (D) aspartate aminotransferase (AST); (E) cholesterol (CHOL); (F) creatine kinase (CK); (G) total protein (TP); (H) creatinine (CRE); (I) uric acid (UA); (J) urea (UREA). Standard error of mean (SEM). Note: all data are presented as mean ± SEM (n = 8).

Figure 6

Confocal imaging (top) and bright-field (bottom) images of myocardial tissue following 24 h incubation with different Yb/Tm/GZO@SiO₂ contents. (a, d) 1 mg/kg, (b, e) 6 mg/kg, and (c, f) 10 mg/kg. The excitation at 980 nm was provided from a pulsed laser, and the red emission was captured by channel set at 640–660 nm (120 × 10 oil lens, scale bar = 50 μm).