Abstract
We present a systematic study on the effect of surface ligands on the luminescence properties and colloidal stability of β-NaYF4:Yb(3+),Er(3+) upconversion nanoparticles (UCNPs), comparing nine different surface coatings to render these UCNPs water-dispersible and bioconjugatable. A prerequisite for this study was a large-scale synthetic method that yields ∼2 g per batch of monodisperse oleate-capped UCNPs providing identical core particles. These ∼23 nm sized UCNPs display an upconversion quantum yield of ∼0.35% when dispersed in cyclohexane and excited with a power density of 150 W cm(-2), underlining their high quality. A comparison of the colloidal stability and luminescence properties of these UCNPs, subsequently surface modified with ligand exchange or encapsulation protocols, revealed that the ratio of the green (545 nm) and red (658 nm) emission bands determined at a constant excitation power density clearly depends on the surface chemistry. Modifications relying on the deposition of additional (amphiphilic) layer coatings, where the initial oleate coating is retained, show reduced non-radiative quenching by water as compared to UCNPs that are rendered water-dispersible via ligand exchange. Moreover, we could demonstrate that the brightness of the upconversion luminescence of the UCNPs is strongly affected by the type of surface modification, i.e., ligand exchange or encapsulation, yet hardly by the chemical nature of the ligand.
Highlights
Lanthanide-doped upconverting nanoparticles (UCNPs) have gained much attention as a promising class of novel labels and probes in bioanalytical and theranostic applications.[1,2,3,4] The sequential absorption of multiple low energy excitation photons by lanthanide ions incorporated into an inorganic host material results in anti-Stokes emission, referred to as upconversion luminescence (UCL).[5]
We present a systematic study on the effect of surface ligands on the luminescence properties and colloidal stability of β-NaYF4:Yb3+,Er3+ upconversion nanoparticles (UCNPs), comparing nine different surface coatings to render these UCNPs water-dispersible and bioconjugatable
A comparison of the colloidal stability and luminescence properties of these UCNPs, subsequently surface modified with ligand exchange or encapsulation protocols, revealed that the ratio of the green (545 nm) and red (658 nm) emission bands determined at a constant excitation power density clearly depends on the surface chemistry
Summary
Lanthanide-doped upconverting nanoparticles (UCNPs) have gained much attention as a promising class of novel labels and probes in bioanalytical and theranostic applications.[1,2,3,4] The sequential absorption of multiple low energy excitation photons by lanthanide ions incorporated into an inorganic host material results in anti-Stokes emission, referred to as upconversion luminescence (UCL).[5]. Besides a preferably high upconversion efficiency under application-relevant conditions, which requires synthetic strategies yielding high quality spherical and monodisperse UCNPs of pure crystallinity and exact stoichiometric composition, there are several other requirements that must be fulfilled by UCNPs for use in bioanalytical and biological applications These include water dispersibility, high colloidal stability, the possibility of subsequent (bio)functionalization, and good bio-compatibility.[15] These require post synthetic treatments and the introduction of hydrophilic and bioconjugatable ligands,[16] as current advanced synthetic strategies for the preparation of high-quality lanthanide-doped hexagonal (= β-phase) NaYF4 UCNPs are based on oil-phase methods, yielding hydrophobic UCNPs.[15,17,18]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
