Core–shell hybrid upconversion nanoparticles carrying stable nitroxide radicals as potential multifunctional nanoprobes for upconversion luminescence and magnetic resonance dual-modality imaging

Abstract

Nitroxide radicals, such as 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) and its derivatives, have recently been used as contrast agents for magnetic resonance imaging (MRI) and electron paramagnetic resonance imaging (EPRI). However, their rapid one-electron bioreduction to diamagnetic N-hydroxy species when administered intravenously has limited their use in in vivo applications. In this article, a new approach of silica coating for carrying stable radicals was proposed. A 4-carboxyl-TEMPO nitroxide radical was covalently linked with 3-aminopropyl-trimethoxysilane to produce a silanizing TEMPO radical. Utilizing a facile reaction based on the copolymerization of silanizing TEMPO radicals with tetraethyl orthosilicate in reverse microemulsion, a TEMPO radicals doped SiO2 nanostructure was synthesized and coated on the surface of NaYF4:Yb,Er/NaYF4 upconversion nanoparticles (UCNPs) to generate a novel multifunctional nanoprobe, PEGylated UCNP@TEMPO@SiO2 for upconversion luminescence (UCL) and magnetic resonance dual-modality imaging. The electron spin resonance (ESR) signals generated by the TEMPO@SiO2 show an enhanced reduction resistance property for a period of time of up to 1 h, even in the presence of 5 mM ascorbic acid. The longitudinal relaxivity of PEGylated UCNPs@TEMPO@SiO2 nanocomposites is about 10 times stronger than that for free TEMPO radicals. The core-shell NaYF4:Yb,Er/NaYF4 UCNPs synthesized by this modified user-friendly one-pot solvothermal strategy show a significant enhancement of UCL emission of up to 60 times more than the core NaYF4:Yb,Er. Furthermore, the PEGylated UCNP@TEMPO@SiO2 nanocomposites were further used as multifunctional nanoprobes to explore their performance in the UCL imaging of living cells and T1-weighted MRI in vitro and in vivo.

Nd3+ sensitized core-shell-shell nanocomposites loaded with IR806 dye for photothermal therapy and up-conversion luminescence imaging by a single wavelength NIR light irradiation

“…From the TEM images we were able to estimate the volumes of the core and shells in these NPs according to a literature publised method with minor modifications 73 (Method S1, Supplementary materials ). At the added 1:1:2 mole ratio for the core:first shell:second shell starting material mixtures, the core:first shell:second shell volume ratio was found to be about 1:0.88:1.64 after the reaction and purification, indicating that the loading efficiency was gradually reduced as the number of shells was increased from one to two.…”

Recent Advances in Magnetic Upconversion Nanocomposites for Bioapplications

“…As iron oxide-based MNPs can always reduce the upconversion luminescence to some extent, alternatives have also been reported recently. Chen et al [41] [42] to construct core-shell structured nanoprobes for UCL/MRI bimodal bioimaging.…”

Micellization of Photo-Responsive Block Copolymers

“…For direct modification of these photo-responsive chromophores via UCNPs, the reader is referred to a recent review by Wu and Butt [178]. However, statistical copolymers having spiropyranes incorporated have been already attached to UCNP by Chen and coworkers [179]. These nanoparticles were used to polymerize poly(NIPAAm- co -spiropyrane methacrylate) and reversible switching of spiropyrane to the merocyanine form was achieved upon irradiation with light at 980 nm [180].…”