Dissolution and Phosphate-Induced Transformation of ZnO Nanoparticles in Synthetic Saliva Probed by AGNES without Previous Solid–Liquid Separation. Comparison with UF-ICP-MS

Abstract

The variation over time of free Zn 2+ ion concentration in stirred dispersions of ZnO nanoparticles (ZnO NPs) prepared in synthetic saliva at pH 6.80 and 37º C was followed in situ (without solid-liquid separation step) with the electroanalytical technique AGNES (Absence of Gradients and Nernstian Equilibrium Stripping). At these conditions, ZnO NPs are chemically unstable due to their reaction with phosphates. The initial stage of transformation (around 5-10 h) involves the formation of a metastable solid (presumably ZnHPO4), which later evolves into the more stable hopeite phase. The overall decay rate of ZnO NPs is significantly reduced in comparison with phosphate-free background solutions of the same ionic strength and pH. The effective equilibrium solubilities of ZnO (0.29-0.47 mg•L-1), as well as conditional excess-ligand stability constants and fractional distributions of soluble Zn species were determined in absence and presence of organic components. The results were compared with the conventional ultrafiltration and inductively coupled plasmamass spectrometry (UF-ICP-MS) methodology. AGNES proves to be advantageous in terms of speed, reproducibility and access to speciation information.

Aged Zinc Oxide Nanoparticles Did Not Induce Cytotoxicity Through Apoptosis Signaling Pathway as Fresh NPs

“…And the protein adsorbed by ZnO NPs formed a special protein crown, which affected its biological effect [25]. Phosphates widely present in physiological solutions (such as saliva) could convert ZnO NPs into metastable ZnHPO 4 and Zn 3 (PO 4 ) 2 within about 5-10 h, and showed cytotoxicity to digestive tract epithelial cells [16]. Ivasket al proved the occurrence of complete transformation of ZnO NPs (≤ 3 µg/mL) in the in vitro exposure system to human T lymphocytes (37 °C, cell culture medium RPMI1640 containing 10% FBS for 24 h) using synchrotron radiation X-ray absorption near-edge structure spectroscopy (XANES).…”

“…And the protein adsorbed by ZnO NPs forms a special protein crown, which affects its biological effect [15]. Phosphates in physiological solutions could convert ZnO NPs into metastable ZnHPO 4 and Zn 3 (PO 4 ) 2 within about 5-10 h [16].The occurrence of complete transformation of ZnO NPs (≤ 3 µg/mL) in the in vitro exposure system to human T lymphocytes (37 °C, cell culture medium RPMI1640 containing 10% FBS for 24 h) was investigated by using synchrotron radiation X-ray absorption near-edge structure spectroscopy (XANES) [17]. The above studies suggest that it is not enough to study pristine (fresh) NPs to assess their environmental and health risks.…”

Dissolution kinetics of zinc oxide and its relationship with physicochemical characteristics

“…The authors report the difficulties to assess kinetics in these media due to their complexity. Nevertheless, pH and temperature are key parameters influencing dissolution of metals in in vitro assays, and biological medium may have constituents, such as organic and inorganic ligands that may increase or decrease dissolution, and therefore impact understanding the dissolution mechanism of compounds [19,20].…”

The Role of Apoptosis Pathway in the Cytotoxicity Induced by Fresh and Aged Zinc Oxide Nanoparticles

“…And the protein adsorbed by ZnO NPs formed a special protein crown, which affected its biological effect [ 19 ]. Phosphates widely present in physiological solutions (such as saliva) could convert ZnO NPs into metastable ZnHPO 4 and Zn 3 (PO 4 ) 2 within about 5–10 h and showed cytotoxicity to digestive tract epithelial cells [ 20 ]. Ivask et al proved the occurrence of complete transformation of ZnO NPs (≤ 3 μg/mL) in the in vitro exposure system to human T lymphocytes (37 °C, cell culture medium RPMI1640 containing 10% FBS for 24 h) using synchrotron radiation X-ray absorption near-edge structure spectroscopy (XANES).…”