Rare earth luminescent materials have attracted extensive attention in the biomedical field as noncontact temperature monitoring devices with microscopic resolution due to their properties in the visible and near-infrared regions. At the application level, it is required to have a certain temperature monitoring capability in the near-infrared region II window to enhance the tissue penetration depth. Here, two kinds of YOFs: Er 3 + , Yb 3 + were prepared by co-precipitation and hydrothermal method, and the luminescence was enhanced by ion doping. An Er 3 + -based ratiometric nanothermometer of 4 F 9 ∕ 2 → 4 I 1 5 ∕ 2 (672 nm, upconversion luminescence) to 4 I 1 3 ∕ 2 → 4 I 1 5 ∕ 2 (1580 nm/1566 nm, NIR II downshifting luminescence) were designed with the Stark energy level. When doped with 2% Zn 2 + , the relative temperature sensitivity of YOF prepared by co-precipitation method was improved from 0.30% ∘ C − 1 (30 ∘ C) to 0.59% ∘ C − 1 (30 ∘ C), expanding its use as a temperature monitoring device possibility. The temperature sensitivity of YOF prepared by hydrothermal method was 1.01% ∘ C − 1 (30 ∘ C). Finally, the NIR II luminescence of the prepared nanothermometer was used as a control for temperature monitoring of heating sites in mice. The results showed that it can distinguish heating site from control site and no significant cytotoxicity or damage to the tissues was revealed, indicating its broad prospects in the biomedical field and other temperature monitoring scenarios in the future.
Traditional optical temperature sensors rely on strong fluorescence emission materials, high-homogeneity nanoparticles, and individual temperature calibration to ensure measurement accuracy and reliability. However, these requirements inevitably introduce disadvantages such as significant time costs, extensive labor inputs, and challenges in material synthesis, which hinder large-scale applications. Consequently, this paper investigates the effects of size, homogeneity, metal doping, and core-shell structures of rare-earth nanoparticles on the thermally coupled energy levels ( 2 H 11/2 and 4 S 3/2 ) of Er-based upconversion nanoparticles (UCNPs). The nanoparticles NaLuF 4 :Yb,Er, NaLuF 4 :Yb,Er,Li, NaLuF 4 :Yb,Er,Mg and NaLuF 4 :Yb,Er@NaLuF 4 :Yb,Tm@NaLuF 4 were prepared using a thermal decomposition method. The morphology and luminescence properties of the four UCNPs were characterized through transmission electron microscopy and fluorescence spectrophotometry. Additionally, variable-temperature luminescence intensity measurements of the four UCNPs were conducted under 980 nm laser excitation. The experimental results demonstrate a strong linear relationship between temperature and the luminescence intensity ratios (LIRs) of the thermally coupled energy levels of Er-based UCNPs with varying shapes, sizes, core-shell structures, and luminescence intensities. Notably, the fitted straight lines relating LIR for different Er-based UCNPs to temperature exhibit approximately equal slopes (sensitivity). This characteristic allows for the calibration of thermometers using only a single temperature point, significantly simplifying the calibration process. Furthermore, the synthesis of the materials is streamlined, enabling mass production without the need to consider the homogeneity and symmetry of the material. Therefore, thermometers based on rare-earth Er-based UCNPs hold significant potential for large-scale production and application.
Highly sensitive and specific discrimination of brain tumor margins from the surrounding parenchyma remains a formidable challenge. Limited by the short of photostable probes with deep tissue penetration and high efficiency of crossing the blood-brain-barrier (BBB), the development of fluorescence-guided surgery (FGS) of brain tumors was markedly constrained. Herein, we report the capability of the strong second near-infrared-IIb (NIR IIb, 1500−1700 nm) fluorescence from Er-based lanthanide nanoparticles in imaging-guided surgery of orthotopic glioma. We designed an energy-cascaded Er 3+ -Ce 3+ -A 3+ (A = Yb, Ho, Tm) system and prepared a series of NaErF 4 : [email protected] 4 @NaLuF 4 down-conversion nanoparticles (DCNPs) for optimizing the influence of NaAF 4 interlayer and Ce 3+ dopants. We modified the optimal NaErF 4 :2.5 % [email protected] 4 (0.9 nm)@NaLuF 4 DCNPs with Dye-brush polymer (Dye-BP) to facilitate 4 I 13/2 → 4 I 15/2 transition, which leads to an impressive 675-fold enhancement of 1525 nm fluorescence in aqueous solution under 808 nm excitation due to the excellent energy-cascaded downconversion (ECD), in comparison with that of NaErF 4 nanoparticles. We further modified these highly bright nanoparticles with tumor-targeting angiopep-2 peptide, and efficiently delivered them to the glioma by using the focused ultrasound sonication (FUS) to temporarily open the BBB. We obtained the highest tumor-to-background ratio (TBR = 12.5) ever reported in the targeted NIR IIb fluorescence imaging of small orthotopic glioma (size < 3 mm, depth> 3 mm) through intact skull and scalp, which was drastically improved to ∼150 after cardiac perfusion and craniotomy to ensure the precise resection of tumor. More importantly, the size of glioma measured from the width of fluorescence profile is very close to that from T 2 -weighted MRI images. Our work provides the insights into engineering NIR IIb fluorescence of lanthanide nanoparticles, and demonstrates the great potential of NIR IIb fluorescence imaging-guided surgery of tumor.
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