Abstract
Luminescent lanthanide-containing biocompatible nanosystems represent promising candidates as nanoplatforms for bioimaging applications. Herein, citrate-functionalized calcium-doped terbium phosphate hydrate nanophosphors of the rhabdophane type were prepared at different synthesis times and different Ca2+/Tb3+ ratios by a bioinspired crystallization method consisting of thermal decomplexing of Ca2+/Tb3+/citrate/phosphate/carbonate solutions. Nanoparticles were characterized by XRD, TEM, SEM, HR-TEM, FTIR, Raman, Thermogravimetry, inductively coupled plasma spectroscopy, thermoanalysis, dynamic light scattering, electrophoretic mobility, and fluorescence spectroscopy. They displayed ill-defined isometric morphologies with sizes ≤50 nm, hydration number n ~ 0.9, tailored Ca2+ content (0.42–8.11 wt%), and long luminescent lifetimes (800–2600 µs). Their relative luminescence intensities in solid state are neither affected by Ca2+, citrate content, nor by maturation time for Ca2+ doping concentration in solution below 0.07 M Ca2+. Only at this doping concentration does the maturation time strongly affect this property, decreasing it. In aqueous suspensions, neither pH nor ionic strength nor temperature affect their luminescence properties. All the nanoparticles displayed high cytocompatibility on two human carcinoma cell lines and cell viability correlated positively with the amount of doping Ca2+. Thus, these nanocrystals represent promising new luminescent nanoprobes for potential biomedical applications and, if coupled with targeting and therapeutic moieties, they could be effective tools for theranostics.
Highlights
Mainly organic dyes, and nanomaterials including semiconductor quantum dots, nanodiamonds, gold nanoparticles [2,3,4], several nanostructures labeled with organic dyes [5], and more recently calcium phosphate apatite nanoparticles both labeled with organic dyes [6] or doped with luminescent lanthanides (Ln3+ ) ions [7,8], have been proposed for these applications
The X-ray powder diffraction (XRD) patterns of the solids precipitated for increasing concentration of Ca2+ (x, from 0.01 M to 0.07 M) and increasing maturation times are reported in
Cit-Ca2+ :TbPO4 ·nH2 O nanocrystals of the hexagonal rhabdophane phase, with n ~ 0.9 and tailored Ca2+ content between 0.42 and 8.11 wt% were successfully obtained by thermal decomplexing of Ca2+ /Tb3+ /citrate/phosphate/carbonate solutions
Summary
Mainly organic dyes, and nanomaterials including semiconductor quantum dots, nanodiamonds, gold nanoparticles [2,3,4], several nanostructures labeled with organic dyes [5], and more recently calcium phosphate apatite nanoparticles (nAp) both labeled with organic dyes [6] or doped with luminescent lanthanides (Ln3+ ) ions [7,8], have been proposed for these applications. ) started to attract much attention because they combine the very low solubility and high thermal conductivity of the metal phosphates as host matrices with the favorable features of the luminescent lanthanide ions, such as sharp emission bands, Stokes shift of hundreds of nanometers, and luminescence lifetimes of the order of milliseconds
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