Abstract
We studied the dissolution behavior of β NaYF4:Yb(20%), Er(2%) UCNP of two different sizes in biologically relevant media i.e., water (neutral pH), phosphate buffered saline (PBS), and Dulbecco’s modified Eagle medium (DMEM) at different temperatures and particle concentrations. Special emphasis was dedicated to assess the influence of different surface functionalizations, particularly the potential of mesoporous and microporous silica shells of different thicknesses for UCNP stabilization and protection. Dissolution was quantified electrochemically using a fluoride ion selective electrode (ISE) and by inductively coupled plasma optical emission spectrometry (ICP OES). In addition, dissolution was monitored fluorometrically. These experiments revealed that a thick microporous silica shell drastically decreased dissolution. Our results also underline the critical influence of the chemical composition of the aqueous environment on UCNP dissolution. In DMEM, we observed the formation of a layer of adsorbed molecules on the UCNP surface that protected the UCNP from dissolution and enhanced their fluorescence. Examination of this layer by X-ray photoelectron spectroscopy (XPS) and mass spectrometry (MS) suggested that mainly phenylalanine, lysine, and glucose are adsorbed from DMEM. These findings should be considered in the future for cellular toxicity studies with UCNP and other nanoparticles and the design of new biocompatible surface coatings.
Highlights
We studied the dissolution behavior of β NaYF4:Yb(20%), Er(2%) upconversion nanoparticles (UCNP) of two different sizes in biologically relevant media i.e., water, phosphate buffered saline (PBS), and Dulbecco’s modified Eagle medium (DMEM) at different temperatures and particle concentrations
The investigation of organic molecules adsorbed on the surface of UCNP aged in DMEM was conducted by X-ray photoelectron spectroscopy (XPS) and mass spectrometry (MS)
Ligand exchange was supported by zeta potential measurements as shown in the supplementary information (Table S3, SI). 20 nm and 30 nm-sized β-NaYF4:20%Yb3+, 2%Er3+ UCNP with different surface chemistries were dispersed in concentrations of 5 and 50 mg/L in water, PBS, and DMEM and aged for time intervals of 6, 15, 24, 48, and 72 h at room temperature and at 37 °C
Summary
We studied the dissolution behavior of β NaYF4:Yb(20%), Er(2%) UCNP of two different sizes in biologically relevant media i.e., water (neutral pH), phosphate buffered saline (PBS), and Dulbecco’s modified Eagle medium (DMEM) at different temperatures and particle concentrations. 20 nm and 30 nm-sized β-NaYF4:20%Yb3+, 2%Er3+ UCNP with different surface chemistries were dispersed in concentrations of 5 and 50 mg/L in water, PBS, and DMEM and aged for time intervals of 6, 15, 24, 48, and 72 h at room temperature and at 37 °C.
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