The influence of NaYF₄:Yb,Er size/phase on the multimodality of co-encapsulated magnetic photon-upconverting polymeric nanoparticles

Abstract

We report the synthesis, characterisation and evaluation of the in vitro biocompatibility of polymeric nanoparticles with both magnetic and upconverting fluorescent properties. The particles consist of superparamagnetic iron oxide nanoparticles and upconverting NaYF4:Yb,Er nanoparticles co-encapsulated within a poly(glycidyl methacrylate) sphere. Two different upconverting nanoparticles (10 nm α-NaYF4:Yb,Er and 50 nm β-NaYF4:Yb,Er) were synthesised and the optical and magnetic properties of the composite polymeric nanoparticle systems assessed by near infra-red laser spectroscopy, SQUID magnetometry and proton relaxometry. A live-dead assay was used to assess the viability of PC-12 neural cells incubated with varying concentrations of the nanoparticles. The composite nanoparticles produced no observed impact on cellular viability even at concentrations as high as 1000 μg mL(-1). Confocal microscopy revealed uptake of nanoparticles by PC-12 cells and peri-nuclear cytoplasmic localisation. Both particle systems show favourable magnetic properties. However, only the nanospheres containing 50 nm β-NaYF4:Yb,Er were suitable for optical tracking because the presence of iron oxide within the composites imparts a significant quenching of the upconversion emission. This study demonstrates the size and phase of the upconverting nanoparticles are important parameters that have to be taken into account in the design of multimodal nanoparticles using co-encapsulation strategies.

An overview of nanoparticles commonly used in fluorescent bioimaging

“…An important recent finding is the effect of the size and the phase on the multimodality of co-encapsulated magnetic photonupconverting polymeric NPs for use in bimodal (fluorescent/ magnetic resonance) imaging. 256 In another sophisticated approach, the large potential of multimodal functionality was impressively demonstrated 257 by showing that NPs of the layer architecture UCNP@mSiO 2 -Ln(dbm) 4 (where mSiO 2 stands for mesoporous silica, Ln for any trivalent ion out of Eu, Sm, Er, Nd, Yb; and dbm stands for the organic ligand complexing the Ln ion). Both downconversion and upconversion luminescence are found, and this results in multicolor emission (covering the spectral region from 450 nm to 1700 nm) under visible-light excitation and 980 nm excitation, respectively.…”

Polymeric nanocapsules with up-converting nanocrystals cargo make ideal fluorescent bioprobes

“…We are, however, proposing a new approach for the construction of theranostic agents, which goes beyond the archetype of a single NP being functionalized with ligands or functional molecules, and envisage various types of nanocontainers as universal therapeutic and diagnostic cargo carriers. In fact, polymeric nanocarriers with sizes lower than 200 nm have been receiving increasing attention as containers for hydrophobic NPs encapsulation, providing good solubility, high long-term stability and loading capacity as well as ability of sustained release of active cargo 7 8 9 . There are numerous biological benefits of simultaneous multiple NPs encapsulation including (i) their improved and prolonged biodistribution in the body; (ii) enhanced biocompatibility and (iii) better internalization by tumor cells 10 11 .…”

Poly(glycidyl methacrylate) coated dual mode upconverting nanoparticles for neuronal cell imaging

“…The attachment of cationic polymers to the surface of polymeric nanoparticles has long been established as an integral modification to enhance nanoparticle interaction with cells and in turn cellular uptake. 22,24,25 In the present case,…”