Abstract
Dual labeled contrast agents could provide better complementary information for bioimaging than available solely from a single modality. In this paper we investigate the suitability of Yb3+ and Er3+-doped BaYF5 upconversion nanoparticles (UCNPs) as both optical and X-ray micro computed tomography (μCT) contrast agents. Stable, aqueous UCNP dispersions were synthesised using a hydrothermal method with the addition of polyethyleneimine (PEI). UCNPs were single crystal and had a truncated cuboidal and/or truncated octahedral morphology, with average particle size of 47 ±9 nm from transmission electron microscopy which was further used to characterize the structure and composition in detail. A zeta potential value of +51 mV was measured for the aqueous nanoparticle dispersions which is beneficial for cell permeability. The outer hydrated PEI layer is also advantageous for the attachment of proteins for targeted delivery in biological systems. The prepared UCNPs were proven to be non-toxic to endothelial cells up to a concentration of 3.5 mg/mL, when assessed using an MTT assay. The particles showed intense green upconversion photoluminescence when excited at a wavelength of 976 nm using a diode laser. Quantitative X-ray μCT contrast imaging confirmed the potential of these UCNPs as X-ray contrast agents and confirming their dual modality for bioimaging.
Highlights
Upconversion (UC) is a process that converts two or more lowerenergy photons in the near-infrared wavelengths into one higher en ergy photon in the visible or ultraviolet (UV) wavelengths [1]
Nano particles doped with lanthanide ions that can produce efficient upconversion are known as upconversion nanoparticles (UCNPs) and have been proven to be useful as fluorescent labels for biomedical im aging [1,2,3,4,5]
The lanthanide ion-doped barium yttrium fluoride system has been proposed as a host material due to the structural as well as optical properties [14,18,19,20]; it is reported that bulk BaYF5 doped with Er3+ can present approximately eight times the UC emission than that of Er3+-doped LaF3 nanocrystals [21]
Summary
Upconversion (UC) is a process that converts two or more lowerenergy photons in the near-infrared wavelengths into one higher en ergy photon in the visible or ultraviolet (UV) wavelengths [1]. The lanthanide ion-doped barium yttrium fluoride system has been proposed as a host material due to the structural as well as optical properties [14,18,19,20]; it is reported that bulk BaYF5 doped with Er3+ can present approximately eight times the UC emission than that of Er3+-doped LaF3 nanocrystals [21]. Syntheses of lanthanide-doped BaYF5 nanocrystals have been carried out by codecomposition in organic solvents under inert gas atmosphere and high temperature [18,19,20,21,22,23] Most of these methods produce hydrophobic nanoparticles which need further surface modification for biological. The non-toxic effects of these particles have been established via testing on endothelial cells, which demonstrates the suitability of the particles for use in biological applications
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