Long‐Term Colloidal and Chemical Stability in Aqueous Media of NaYF₄‐Type Upconversion Nanoparticles Modified by Ligand‐Exchange

Abstract

Surface capping is an essential component of nanoparticles as it provides access to their outstanding properties in the real world. Upconversion nanoparticles are predominantly interesting for use in biological environments, due to their excellent optical properties such as the conversion of near‐infrared excitation light into emissions in the visible or UV range of the spectrum, high photostability, and the absence of any intermittence. One of the most efficient upconversion nanoparticles, consisting of lanthanide doped NaYF4, suffers from limited stability in aqueous media. This study investigates a set of five types of surface coatings, ranging from small ligands to polymers of different charge and different coordinating groups, on monodisperse 28 ± 0.9 nm sized NaYF4(Yb,Er) nanoparticles modified by a two‐step ligand exchange mediated by NOBF4. Information on the long‐term chemical and colloidal stability for highly diluted aqueous dispersions of these particles is acquired by transmission electron microscopy, dynamic light scattering, and luminescence spectroscopy. The findings are of importance for the development of probes and labels based on upconversion nanoparticles for biological applications.

Assessing the protective effects of different surface coatings on NaYF4:Yb3+, Er3+ upconverting nanoparticles in buffer and DMEM

“…NaYF 4 :20%Yb 3+ ,2%Er 3+ UCNP were synthesized according to a previously reported procedure 26 – 28 with some modifications 25 , 44 . Surface modifications and silica coating experiments followed published procedures 45 – 49 .…”

Evaluation of Nanoparticle Penetration in the Tumor Spheroid Using Two-Photon Microscopy

“…We investigated the role of MSN physicochemical stability by measuring the fluorescence intensity change in a slightly acid medium (pH~6.5–6.7), which mimicked the tumor microenvironment’s pH. The change in fluorescence stability was related to the MSN’s chemical and/or physical changes, such as the homogeneity, degradation and aggregation of NP in the solution [ 34 ]. The degree of NP dispersity change under a slightly acid medium is shown as the polydispersity index (PDI) values presented in Table S2 .…”

Engineering osteogenic microenvironments by combination of multilayers from collagen type I and chondroitin sulfate with novel cationic liposomes

“…This result indicates a highly positive charged surface, useful as a polycationic component for multilayer formation, as it was shown previously by our group using cationic polymeric particles with a ζ potential of ≈30 mV [ 38 ]. A further advantage is that the positive charge also provides colloidal stability in suspension [ 39 ]. X-ray diffraction studies demonstrated that OO4/DOPE 1/3 forms non-correlated bilayers even at high lipid concentrations due to electrostatic repulsion [ 39 ].…”

“…A further advantage is that the positive charge also provides colloidal stability in suspension [ 39 ]. X-ray diffraction studies demonstrated that OO4/DOPE 1/3 forms non-correlated bilayers even at high lipid concentrations due to electrostatic repulsion [ 39 ]. This behavior causes the tendency to form spontaneously unilamellar vesicles.…”