Multifunctional β-NaGdF₄:Ln³⁺ (Ln = Yb, Er, Dy) nanoparticles with NIR to visible upconversion and high transverse relaxivity: a potential bimodal contrast agent for high-field MRI and optical imaging

Abstract

A novel series of active-core/active-shell upconverting nanoparticles (AC/AS-UCNPs) based on NaGdF 4 doped with Yb 3+ /Er 3+ in the core and Yb 3+ /Dy 3+ in the shell having average particle size between 29.2 and 32.9 nm were synthesized. The UCNPs exhibit favorable properties for bimodal magnetic resonance imaging (MRI) and optical imaging (OI). Excitation of the UCNPs at 980 nm dispersed in water at room temperature resulted in intense green upconversion emission of Er 3+ . The proton nuclear magnetic relaxation dispersion ( 1 H-NMRD) studies show very low longitudinal relaxivity (r 1 ) values, which decreases with an increase of magnetic field. On the other hand, the transverse relaxivity (r 2 ) values show an increasing trend with both increase in doping of Dy 3+ as well as the increase in magnetic field reaching a maximum value of r 2 ¼ 70.07 s À1 mM À1 (per Ln 3+ ion) for NaGdF 4 :Yb 3+ /Er 3+ # NaYbF 4 :38.06% Dy 3+ at 500 MHz and 310 K. Exhibiting such a high r 2 value at high magnetic field and intense upconversion luminescence under 980 nm excitation makes these NPs exceptional candidates towards bioimaging applications.

A Magnetic Chameleon: Biocompatible Lanthanide Fluoride Nanoparticles with Magnetic Field Dependent Tunable Contrast Properties as a Versatile Contrast Agent for Low to Ultrahigh Field MRI and Optical Imaging in Biological Window

“…Typical core–shell nanoparticles, capped with oleic acid (NP‐OA), were obtained by deposition of a NaGdF 4 :Yb/Tm (23/1 mol %) shell over a NaHoF 4 core by a modification of previously reported method . The detailed synthetic procedure adopted is presented in the Experimental section.…”

“…The oleate‐capped core/shell nanoparticles (NP‐OA) were synthesized using a well‐established multi‐step procedure starting with the preparation of the lanthanide‐trifluoroacetate (TFA) precursors, followed by thermal decomposition . Here the lanthanide precursors were generated by the addition of 10 mL of a water/TFA (1:1) mixture to 377.9 mg Ho 2 O 3 (1×10 −3 mol, 50 %) (for core), and a mixture of 276.5 mg Gd 2 O 3 (0.76×10 −3 mol, 38 %) 91.0 mg Yb 2 O 3 (0.23×10 −3 mol, 11.5 %) 3.9 mg Tm 2 O 3 (0.01×10 −3 mol, 0.5 %) (for shell) and the suspensions were left to reflux until solutions became clear .…”

“…One possible solution for this problem is the separate doping of the luminescent Ln 3+ and the paramagnetic Ln 3+ in different layers of core–shell structures. In a previous study, we showed that efficient upconversion luminescence and high T 2 relaxivity can be achieved by selective doping of Yb 3+ /Er 3+ , Dy 3+ ions in separate layers of active‐core/active‐shell upconverting nanoparticles having β‐NaGdF 4 structure …”

Synthesis, Functionalization, and Design of Magnetic Nanoparticles for Theranostic Applications

“…[755] Hence, the anatomic information provided by MRI, as well as functional details of a molecular event can be elucidated through manipulation of fluorescent agents either conjugated or doped within nanoparticles to produce pictures with improved quality. [731b] These optical imaging agents are commonly combined with magnetic nanoparticles, chemically or physically, to produce an end product which retains as a compact ideal probe through its journey toward the target.…”

High‐Field MRI Contrast Agents and their Synergy with Optical Imaging: the Evolution from Single Molecule Probes towards Nano‐architectures

“…Upon excitation of the NPs at 980 nm, strong luminescence was observed as a result of energy migration‐mediated up‐conversion. The MRI/OI performance was facilitated by the Dy 3+ ions playing a dual role, providing T 2 relaxivity and assisting the upconversion process by being an accumulator of energy …”