Core–Shell Lanthanide Upconversion Nanophosphors as Four-Modal Probes for Tumor Angiogenesis Imaging

Multimodality imaging overcomes the shortage and incorporates the advantages of different imaging tools. Lanthanide-based nanoprobes are unique and have rich optical, magnetic, radioactive, and X-ray attenuation properties; however, simple doping of different lanthanide cations into one host can result in a material with multifunction but not the optimized properties. In this study, using NaLuF₄:Yb,Tm as the core and 4 nm of ¹⁵³Sm³⁺-doped NaGdF₄ (half-life of ¹⁵³Sm = 46.3 h) as the shell, we developed a lanthanide-based core–shell nanocomposite as an optimized multimodal imaging probe with enhanced imaging ability. The lifetime of upconversion luminescence (UCL) at 800 nm and relaxation rate (1/<i>T</i>₁) were at 1044 μs and 18.15 s^–1·mM^–1, respectively; however, no significant decrease in the attenuation coefficient was observed, which preserved the excellent X-ray imaging ability. The nanomaterial NaLuF₄:Yb,Tm@NaGdF₄(¹⁵³Sm) was confirmed to be effective and applicable for UCL imaging, X-ray computed tomography (CT), magnetic resonance imaging, and single-photon emission computed tomography (SPECT) <i>in vivo</i>. Furthermore, the NaLuF₄:Yb,Tm@NaGdF₄(¹⁵³Sm) nanoparticles were applied in tumor angiogenesis analysis by combining multimodality imaging of CT, SPECT, and confocal UCL imaging, which shows its value of multifunctional nanoparticles NaLuF₄:Yb,Tm@NaGdF₄(¹⁵³Sm) in tumor angiogenesis imaging

Nd³⁺-Sensitized Upconversion Nanostructure as a Dual-Channel Emitting Optical Probe for Near Infrared-to-Near Infrared Fingerprint Imaging

Lanthanide upconversion nanophosphors (Ln-UCNPs) have attracted great attention in a variety of fields, benefiting from low background fluorescence interference and a high signal-to-noise ratio of upconversion luminescence. However, the establishment of Ln-UCNPs with dual near-infrared (NIR) emission channels still remains challenging. Herein, we report the design and synthesis of Nd³⁺-sensitized NaYbF₄:Tm@NaYF₄:Yb@NaNdF₄:Yb hierarchical-structured nanoparticles that emit NIR luminescence at 696 and 980 nm under excitation at 808 nm. The sensitizer-rich NaYbF₄ core promotes efficient energy transfer to Tm³⁺. The interlayer of NaYF₄:Yb effectively prevents the cross-relaxation process from Tm³⁺ to Nd³⁺ and thus enhances the luminescence emission. The introduction of Nd³⁺ ion as the sensitizer transforms the excitation wavelength from 980 to 808 nm, which subtly averts the laser-induced thermal effect and offers a new pathway for the NIR emission channel at 980 nm. The as-prepared nanoparticles were further applied in developing latent and blood fingerprint images, which exhibited high signal-to-noise ratio and distinguishable details under 808 nm excitation with negligible thermal damage to the sample. Our work provides a promising strategy to realize NIR-to-NIR dual-channel emissions in Ln-UCNPs. With further functionalization, such nanoparticles are expected to have great potential in forensic and biological sciences

Hybrid Nanoclusters for Near-Infrared to Near-Infrared Upconverted Persistent Luminescence Bioimaging

Persistent luminescence (PL) bioimaging provides an optimal method of eliminating autofluorescence for a higher resolution and sensitivity because of the absence of excitation light. However, ultraviolet light is still necessary in common energy charging processes, which limits its reactivation in vivo because of its low penetration depth. In the present study, we introduce a type of hybrid nanocluster (UCPL-NC) composed of upconversion nanoparticles, β-NaYbF₄:Tm@NaYF₄, and persistent nanoparticles, Zn_1.1Ga_1.8Ge_0.1O₄:0.5%Cr, which can be activated by a 980 nm laser and exhibits an afterglow at 700 nm to realize near-infrared (NIR) to NIR UCPL bioimaging. The PL of the UCPL-NCs can be reactivated even when covered with a 10 mm pork. We demonstrate that these polyethylene glycol-modified phospholipid-functionalized UCPL-NCs can be reactivated in vivo and applied in the PL lymphatic imaging on small animals

Highly Enhanced Cooperative Upconversion Luminescence through Energy Transfer Optimization and Quenching Protection

Upconversion luminescence nanomaterials have shown great potential in biological and physical applications because of their unique properties. However, limited research exists on the cooperative sensitization upconversion emission in Tb³⁺ ions over Er³⁺ ions and Tm³⁺ ions because of its low efficiency. Herein, by optimizing the doping ratio of sensitizer and activator to maximize the utilization of the photon energy and introducing the CaF₂ inert shell to shield sensitizer from quenchers, we synthesize ultrasmall NaYbF₄:Tb@CaF₂ nanoparticles with a significant enhancement (690-fold) in cooperative sensitization upconversion emission intensity, compared with the parent NaYbF₄:Tb. The lifetime of Tb³⁺ emission in NaYbF₄:Tb@CaF₂ nanoparticles is prolonged extensively to ∼3.5 ms. Furthermore, NaYbF₄:Tb@CaF₂ was applied in <i>in vitro</i> and <i>in vivo</i> bioimaging. The presented luminescence enhancement strategy provides cooperative sensitization upconversion with new opportunities for bioapplication

17β-Estradiol-Loaded PEGlyated Upconversion Nanoparticles as a Bone-Targeted Drug Nanocarrier

Hormone replacement therapy (HRT) plays an important role in the treatment and prevention of osteoporosis. Here, 17β-estradiol (E2)-loaded PEGlyated upconversion nanoparticles (E2-UCNP@pPEG) were synthesized that retained E2 bioactivity and improved delivery efficiency over a relatively long time-period. E2-UCNP@pPEG was synthesized and characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR), among other methods. The loading efficiency of E2 was determined to be 14.5 wt %, and the nanocarrier effectively facilitated sustained release. Confocal upconversion luminescence (UCL) imaging using the CW 980 nm laser as excitation resource revealed significant interactions of E2-UCNP@pPEG with preosteoblasts. E2-UCNP@pPEG treatment of preosteoblasts induced positive effects on differentiation, matrix maturation, and mineralization. Moreover, in situ and ex vivo UCL imaging studies disclosed that E2 encapsulated in the nanocomposite was passively delivered to bone. Our results collectively suggest that this nanoreservoir provides an effective drug-loading system for hormonelike drug delivery and support its considerable potential as a therapeutic agent for osteoporosis