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3D visualization of additive occlusion and tunable full-spectrum fluorescence in calcite

View Article: PubMed Central - PubMed

ABSTRACT

From biomineralization to synthesis, organic additives provide an effective means of controlling crystallization processes. There is growing evidence that these additives are often occluded within the crystal lattice. This promises an elegant means of creating nanocomposites and tuning physical properties. Here we use the incorporation of sulfonated fluorescent dyes to gain new understanding of additive occlusion in calcite (CaCO3), and to link morphological changes to occlusion mechanisms. We demonstrate that these additives are incorporated within specific zones, as defined by the growth conditions, and show how occlusion can govern changes in crystal shape. Fluorescence spectroscopy and lifetime imaging microscopy also show that the dyes experience unique local environments within different zones. Our strategy is then extended to simultaneously incorporate mixtures of dyes, whose fluorescence cascade creates calcite nanoparticles that fluoresce white. This offers a simple strategy for generating biocompatible and stable fluorescent nanoparticles whose output can be tuned as required.

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Effect of occlusion on photophysical properties of fluorescent dyes.(a) Excitation (dotted) and emission (solid) spectra for aqueous solutions of BLUE (blue), GREEN (green) and RED (red). (b–d) Emission spectra of dye/calcite composites of different initial concentrations of dyes in [Ca2+]=[CO32−]=5 mM experiments (b) BLUE, (c) GREEN and (d) RED. For clarity, the spectra deriving from different starting concentrations of dyes are indicated in the legends.
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f4: Effect of occlusion on photophysical properties of fluorescent dyes.(a) Excitation (dotted) and emission (solid) spectra for aqueous solutions of BLUE (blue), GREEN (green) and RED (red). (b–d) Emission spectra of dye/calcite composites of different initial concentrations of dyes in [Ca2+]=[CO32−]=5 mM experiments (b) BLUE, (c) GREEN and (d) RED. For clarity, the spectra deriving from different starting concentrations of dyes are indicated in the legends.

Mentions: The spectral properties of GREEN in aqueous solution were established with fluorescence spectroscopy, where broad excitation maxima were observed at λex=334 and 415 nm, and an emission maximum at 508 nm was observed on excitation at 415 nm (Fig. 4a). Occlusion of GREEN in calcite crystals precipitated at [Ca2+]=[CO32−]=5 mM resulted in a change in λem from 508 to 512 nm, and additional peaks emerged at longer wavelengths with increasing levels of incorporation (Fig. 4c). Changes in excitation and emission spectra are frequently seen on the occlusion of dyes within crystals due to changes in their conformations or local environments18. For example, rhodamine19, aniline32 and pyrene-based dyes19 occluded in K2SO4 show red shifts in the emission maxima, while blue shifts of absorption maxima and either red or blue shifts in emission maxima were observed for dyes incorporated within potassium dihydrogen phosphate3334. Notably, however, in addition to a small shift in the primary emission maximum, we also observe a significant increase in the intensity of a secondary peak at 550–553 nm with increasing levels of occluded dyes. This spectral change is often observed in more concentrated solutions of dyes, and is attributed to H-type π-stacking353637. As HPTS is anionic under the reaction conditions used, such stacking could be promoted by ion-bridging by Ca2+ ions, and the contribution of π–π stacking. Our data suggest, therefore, that both dye stacking and local environmental changes may contribute to the spectral changes observed here.


3D visualization of additive occlusion and tunable full-spectrum fluorescence in calcite
Effect of occlusion on photophysical properties of fluorescent dyes.(a) Excitation (dotted) and emission (solid) spectra for aqueous solutions of BLUE (blue), GREEN (green) and RED (red). (b–d) Emission spectra of dye/calcite composites of different initial concentrations of dyes in [Ca2+]=[CO32−]=5 mM experiments (b) BLUE, (c) GREEN and (d) RED. For clarity, the spectra deriving from different starting concentrations of dyes are indicated in the legends.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5120221&req=5

f4: Effect of occlusion on photophysical properties of fluorescent dyes.(a) Excitation (dotted) and emission (solid) spectra for aqueous solutions of BLUE (blue), GREEN (green) and RED (red). (b–d) Emission spectra of dye/calcite composites of different initial concentrations of dyes in [Ca2+]=[CO32−]=5 mM experiments (b) BLUE, (c) GREEN and (d) RED. For clarity, the spectra deriving from different starting concentrations of dyes are indicated in the legends.
Mentions: The spectral properties of GREEN in aqueous solution were established with fluorescence spectroscopy, where broad excitation maxima were observed at λex=334 and 415 nm, and an emission maximum at 508 nm was observed on excitation at 415 nm (Fig. 4a). Occlusion of GREEN in calcite crystals precipitated at [Ca2+]=[CO32−]=5 mM resulted in a change in λem from 508 to 512 nm, and additional peaks emerged at longer wavelengths with increasing levels of incorporation (Fig. 4c). Changes in excitation and emission spectra are frequently seen on the occlusion of dyes within crystals due to changes in their conformations or local environments18. For example, rhodamine19, aniline32 and pyrene-based dyes19 occluded in K2SO4 show red shifts in the emission maxima, while blue shifts of absorption maxima and either red or blue shifts in emission maxima were observed for dyes incorporated within potassium dihydrogen phosphate3334. Notably, however, in addition to a small shift in the primary emission maximum, we also observe a significant increase in the intensity of a secondary peak at 550–553 nm with increasing levels of occluded dyes. This spectral change is often observed in more concentrated solutions of dyes, and is attributed to H-type π-stacking353637. As HPTS is anionic under the reaction conditions used, such stacking could be promoted by ion-bridging by Ca2+ ions, and the contribution of π–π stacking. Our data suggest, therefore, that both dye stacking and local environmental changes may contribute to the spectral changes observed here.

View Article: PubMed Central - PubMed

ABSTRACT

From biomineralization to synthesis, organic additives provide an effective means of controlling crystallization processes. There is growing evidence that these additives are often occluded within the crystal lattice. This promises an elegant means of creating nanocomposites and tuning physical properties. Here we use the incorporation of sulfonated fluorescent dyes to gain new understanding of additive occlusion in calcite (CaCO3), and to link morphological changes to occlusion mechanisms. We demonstrate that these additives are incorporated within specific zones, as defined by the growth conditions, and show how occlusion can govern changes in crystal shape. Fluorescence spectroscopy and lifetime imaging microscopy also show that the dyes experience unique local environments within different zones. Our strategy is then extended to simultaneously incorporate mixtures of dyes, whose fluorescence cascade creates calcite nanoparticles that fluoresce white. This offers a simple strategy for generating biocompatible and stable fluorescent nanoparticles whose output can be tuned as required.

No MeSH data available.


Related in: MedlinePlus