Nd³⁺/Yb³⁺ cascade-sensitized single-band red upconversion emission in active-core/active-shell nanocrystals

Abstract

Lanthanide-doped upconversion nanomaterials (UCNMs) have promoted extensive interest for its biological research and biomedical applications, benefiting from low autofluorescence background, deep light penetration depth, and minimal photo-damage to biological tissues. However, owing to the 980 nm laser-induced overheating issue and the attenuation effect associated with conventional multi-peak emissions, the usage of UCNMs as fluorescent bioprobes is still limited. To address these issues, an effective strategy has been proposed to tune both the excitation and emission peaks of UCNMs into the first biological window (650 ∼ 900 nm), where the light absorption by water and hemoglobin in biological tissues is minimal. Based on the Nd/Yb cascade-sensitized upconversion process and efficient exchange-energy transfer between Mn and Er in conjunction with the active-core@active-shell nanostructured design, we have developed a new class of upconversion nanoparticles (UCNPs) that exhibit strong single-band red emission upon excitation of an 808 nm near-infrared laser. Hopefully, the well-designed KMnF:Yb/Er/Nd@ KMnF:Yb/Nd core-shell nanocrystals will be considered a promising alternative to conventionally used UCNPs for biolabeling applications without the concern of the overheating issue and the attenuation constraints.

Biotin-Conjugated Upconversion KMnF3/Yb/Er Nanoparticles for Metabolic Magnetic Resonance Imaging of the Invasive Margin of Glioblastoma

“…Considering the unique MR/UCL bimodal imaging feature of UCNPs, UCL imaging of glioblastoma-bearing brain in vivo and main organs ex vivo was performed at 4 h after injection of biotin/PEG–UCNPs and PEG–UCNPs. In our study, there was no evident fluorescence detectable in glioblastoma-bearing brain in vivo when injected with PEG–UCNPs and biotin/PEG–UCNPs shown in Figure S11 (Supporting Information), which may be due to the limited penetration depth of UCNPs (NIR-I) and the presence of the skull, which exhibit unavoidable and inhomogeneous attenuation caused by tissue scattering or absorption . However, the ex vivo UCL signal from excised glioblastoma-bearing brain was detected in the biotin/PEG–UCNPs group compared with the nontargeted group due to the glioblastoma-targeting ability of biotin.…”

“…In our study, there was no evident fluorescence detectable in glioblastoma-bearing brain in vivo when injected with PEG−UCNPs and biotin/ PEG−UCNPs shown in Figure S11 (Supporting Information), which may be due to the limited penetration depth of UCNPs (NIR-I) and the presence of the skull, which exhibit unavoidable and inhomogeneous attenuation caused by tissue scattering or absorption. 30 However, the ex vivo UCL signal from excised glioblastoma-bearing brain was detected in the biotin/PEG−UCNPs group compared with the nontargeted group due to the glioblastoma-targeting ability of biotin. Meanwhile, the noticeable fluorescence signal of the liver and kidney was observed in the targeted or nontargeted group, indicating that the nanoprobes were mainly metabolized by the liver and kidney, consistent with MRI results in our study.…”

Huge upconversion luminescence enhancement by a cascade optical field modulation strategy facilitating selective multispectral narrow-band near-infrared photodetection

“…Under 808 nm excitation, Nd 3+ ions in the outer shell dominate the absorption and migrate the energy to Yb 3+ ions and subsequently to Tm 3+ ions, giving rise to blue-violet and red emissions 33 . The inert layer of NaYF 4 acts to prevent cross talk between the two emissive areas (the core and the outer shell) 34 . The outermost layer is not optimal, as Nd 3+ has multiple higher energy levels that may effectively accept the energy from excited Tm 3+ ions.…”

“…For the studied upconversion emission lines originating from two- or three-photon processes (Fig. 1d ), n typically varies between 1.0 and 3.0, subject to upconversion saturation 26 , 32 – 34 . Thus, the excitation light intensity amplification through the joint action of the superlensing and plasmonic effects can potentially lead to UCL enhancement by four orders of magnitude for the utilized UCNCs 20 .…”

Improved Red Emission and Short-Wavelength Infrared Luminescence under 808 nm Laser for Tumor Theranostics

“…Specifically, a dual-/multimodal molecular imaging under a single source using a single structure was proposed, which could coordinate the properties of tissue penetration depth, sensitivity, and resolution. − Lanthanide nanoparticles with adjustable absorbance band may achieve a range of biomedical applications, such as anticounterfeiting, − molecular sensing, − bioimaging, − and therapeutics. − Especially, up-conversion nanoparticles (UCNPs) are suitable for bioimaging, which can prevent tissue damage with low photo energy and reduce autofluorescence interference with large anti-Stokes shift. − UCL based on triplet–triplet annihilation can accommodate low excitation pump power with molecularly tunable photophysical properties and high quantum efficiency. − The triplet–triplet annihilation system typically comprises a pair of chromophores: sensitizer and activator. Ln 3+ /Yb 3+ codopant as UCL nanoparticles require an excitation wavelength at around 980 nm, of which the water and organism are absorbed strongly, resulting in the tissue overheating. − Tuning the excitation peak to 808 nm by doping Nd 3+ ions with Ln 3+ /Yb 3+ ions is a good choice to address this problem. − …”