In this study, we synthesized polyacrylic acid (PAA)-Ca (Eu) nanoclusters as a luminescence sensor of phosphate ion by a complex method, and we aimed to achieve the quantitative detection of PO43− based on the sensitivity of the charge transfer band of Eu3+ to anionic ligand. The resulting PAA-Ca(Eu) nanoclusters showed a well-dispersed and a dot-like morphology, with an ultra-small diameter (the average size of 2.17 nm) under high resolution transmission electron microscopy(HRTEM) observation. A dynamic light scattering particle size analyzer (DLS) showed a hydrodynamic size of 2.39 nm. The (PAA)-Ca (Eu) nanoclusters as a luminescence sensor showed a significantly higher sensitivity for PO43− than other anions (CO32−, SiO32−, SO42−, SO32−, Br−, Cl−, F−). The luminescence intensity displayed a linear increase (y = 19.32x + 74.75, R2 > 0.999) in a PO43 concentration range (0–10 mM) with the concentration of PO43− increase, and the limit of detection was 0.023 mM. The results showed good recovery rates and low relative standard deviations. These (PAA)-Ca (Eu) nanoclusters are hopeful to become a luminescence sensor for quantitatively detecting PO43−.
Initial-stage prenucleation clusters (PNCs) are critical
in calcium
phosphate (CaP) biomineralization and thus the formation mechanisms
of human bones and teeth. However, several features of PNCs require
further examination, e.g., structure, ionic stoichiometry, kinetics,
thermodynamics, and nucleation mechanism. In this study, we used poly(acrylic
acid) (PAA)–Ca(Eu) complexes with partial Eu3+ substitution
as pre-PNCs and established a fluorescence method to study PNC formation
in situ based on Eu–O charge-transfer transitions. The kinetics
and thermodynamics of PNC formation were explored by probing the fluorescence
changes of Eu–O charge-transfer transitions during bonding
between the pre-PNCs and PO4
3–. PNC formation
was consistent with the pseudo-second-order kinetic and Langmuir isothermal
adsorption models. The flexible structures of PNCs aided in regulating
the subsequent nucleation and crystallization. This study provides
an in situ fluorescence probing method with critical guiding significance
in addressing the features of PNC formation, in addition to biomineralization.
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