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

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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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Fluorescent dye/calcite composite nanoparticles.(a) Representative TEM micrograph of calcite nanoparticles occluding GREEN and selected-area electron diffraction pattern (inset). (b) Powder X-ray diffraction analysis of calcite nanoparticles demonstrating wide-line broadening associated with small crystalline domain size (τ=53 nm). (c–f) photographs of ethanolic suspensions of fluorescent calcite nanoparticles containing (c) BLUE, (d) GREEN, (e) RED and (f) dye mixture under normal light (top) and ultraviolet light (365 nm, bottom). (g) Emission spectra of ethanolic suspensions of calcite nanoparticles occluding BLUE (blue, λex=360 nm), GREEN (green, λex=430 nm), RED (orange, λex=512 nm) and dye mixture (black, λex=360 nm; section at ∼700–760 nm removed due to signal from excitation light at 2λex). Scale bar, 100 nm (a).
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f8: Fluorescent dye/calcite composite nanoparticles.(a) Representative TEM micrograph of calcite nanoparticles occluding GREEN and selected-area electron diffraction pattern (inset). (b) Powder X-ray diffraction analysis of calcite nanoparticles demonstrating wide-line broadening associated with small crystalline domain size (τ=53 nm). (c–f) photographs of ethanolic suspensions of fluorescent calcite nanoparticles containing (c) BLUE, (d) GREEN, (e) RED and (f) dye mixture under normal light (top) and ultraviolet light (365 nm, bottom). (g) Emission spectra of ethanolic suspensions of calcite nanoparticles occluding BLUE (blue, λex=360 nm), GREEN (green, λex=430 nm), RED (orange, λex=512 nm) and dye mixture (black, λex=360 nm; section at ∼700–760 nm removed due to signal from excitation light at 2λex). Scale bar, 100 nm (a).

Mentions: Finally, our concept of fluorescent dye occlusion was extended to calcite nanoparticles. These were formed via a modified carbonation method (Supplementary Figs 14 and 15)42, and TEM and powder X-ray diffraction analysis revealed 55 nm calcite particles (Fig. 8 and Supplementary Fig. 16). The synthesis was performed in the presence of individual or mixtures of dyes, and neither the morphologies nor particle sizes were significantly affected by the presence of dye. The calcite nanoparticles exhibited bright fluorescence from both dried nanoparticles (Supplementary Fig. 17) and ethanolic suspensions (Fig. 8c–g) on excitation with ultraviolet light, where the emitted light was dependent on the dye (or mixture of dyes) present during nanoparticle growth. Quantification of the amounts of fluorescent dye occluded revealed an identical trend to that seen for micron-scale calcite (that is, RED>BLUE>GREEN) (Supplementary Table 2), and no significant differences in the spectroscopic data were observed as compared with the micron-scale calcite crystals. The fluorescence lifetime of GREEN in nanoparticulate calcite was τ=3.0 ns, which is comparable to values obtained for internal regions of calcite single crystals grown from [Ca2+]=[CO32−]=2.5 mM.


3D visualization of additive occlusion and tunable full-spectrum fluorescence in calcite
Fluorescent dye/calcite composite nanoparticles.(a) Representative TEM micrograph of calcite nanoparticles occluding GREEN and selected-area electron diffraction pattern (inset). (b) Powder X-ray diffraction analysis of calcite nanoparticles demonstrating wide-line broadening associated with small crystalline domain size (τ=53 nm). (c–f) photographs of ethanolic suspensions of fluorescent calcite nanoparticles containing (c) BLUE, (d) GREEN, (e) RED and (f) dye mixture under normal light (top) and ultraviolet light (365 nm, bottom). (g) Emission spectra of ethanolic suspensions of calcite nanoparticles occluding BLUE (blue, λex=360 nm), GREEN (green, λex=430 nm), RED (orange, λex=512 nm) and dye mixture (black, λex=360 nm; section at ∼700–760 nm removed due to signal from excitation light at 2λex). Scale bar, 100 nm (a).
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f8: Fluorescent dye/calcite composite nanoparticles.(a) Representative TEM micrograph of calcite nanoparticles occluding GREEN and selected-area electron diffraction pattern (inset). (b) Powder X-ray diffraction analysis of calcite nanoparticles demonstrating wide-line broadening associated with small crystalline domain size (τ=53 nm). (c–f) photographs of ethanolic suspensions of fluorescent calcite nanoparticles containing (c) BLUE, (d) GREEN, (e) RED and (f) dye mixture under normal light (top) and ultraviolet light (365 nm, bottom). (g) Emission spectra of ethanolic suspensions of calcite nanoparticles occluding BLUE (blue, λex=360 nm), GREEN (green, λex=430 nm), RED (orange, λex=512 nm) and dye mixture (black, λex=360 nm; section at ∼700–760 nm removed due to signal from excitation light at 2λex). Scale bar, 100 nm (a).
Mentions: Finally, our concept of fluorescent dye occlusion was extended to calcite nanoparticles. These were formed via a modified carbonation method (Supplementary Figs 14 and 15)42, and TEM and powder X-ray diffraction analysis revealed 55 nm calcite particles (Fig. 8 and Supplementary Fig. 16). The synthesis was performed in the presence of individual or mixtures of dyes, and neither the morphologies nor particle sizes were significantly affected by the presence of dye. The calcite nanoparticles exhibited bright fluorescence from both dried nanoparticles (Supplementary Fig. 17) and ethanolic suspensions (Fig. 8c–g) on excitation with ultraviolet light, where the emitted light was dependent on the dye (or mixture of dyes) present during nanoparticle growth. Quantification of the amounts of fluorescent dye occluded revealed an identical trend to that seen for micron-scale calcite (that is, RED>BLUE>GREEN) (Supplementary Table 2), and no significant differences in the spectroscopic data were observed as compared with the micron-scale calcite crystals. The fluorescence lifetime of GREEN in nanoparticulate calcite was τ=3.0 ns, which is comparable to values obtained for internal regions of calcite single crystals grown from [Ca2+]=[CO32−]=2.5 mM.

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