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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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GREEN/calcite host–guest composites.(a,f,k) Representative SEM micrographs of GREEN/calcite composite crystals precipitated under the conditions (a–e=[Ca2+]=[CO32−]=25 mM and [GREEN]=0.1 mM; f–j=[Ca2+]=[CO32−]=5 mM and [GREEN]=0.1 mM; and k–o=[Ca2+]=[HCO3−]=3.5 mM and [GREEN]=0.1 mM). (b,g,l) Three-dimensional (3D) representation of the morphologies of the crystals imaged in c,h,m, with approximate faces labelled, and the growth sectors coloured in green. The + and − labels denote obtuse and acute step morphologies, respectively. (c,h,m) Confocal fluorescence micrographs of composite crystals grown under the conditions. (d,i,n) Orthogonal views (XY, YZ and XZ) of composites obtained from z-stacked confocal micrographs, showing the distribution of dye in 3D (z+ direction is away from the substrate, XY is the imaging plane) Colour scale: blue (low intensity) to red (high intensity); black, no signal; White, detector saturation. (e,j,o) Line profiles (e) and intensity histograms (j,o) corresponding to the lines or regions shown on the orthogonal view images in (d,i,n) respectively. Scale bars, 15 μm (a); 10 μm (f); 25 μm (k); 20 μm (c,h,m).
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f1: GREEN/calcite host–guest composites.(a,f,k) Representative SEM micrographs of GREEN/calcite composite crystals precipitated under the conditions (a–e=[Ca2+]=[CO32−]=25 mM and [GREEN]=0.1 mM; f–j=[Ca2+]=[CO32−]=5 mM and [GREEN]=0.1 mM; and k–o=[Ca2+]=[HCO3−]=3.5 mM and [GREEN]=0.1 mM). (b,g,l) Three-dimensional (3D) representation of the morphologies of the crystals imaged in c,h,m, with approximate faces labelled, and the growth sectors coloured in green. The + and − labels denote obtuse and acute step morphologies, respectively. (c,h,m) Confocal fluorescence micrographs of composite crystals grown under the conditions. (d,i,n) Orthogonal views (XY, YZ and XZ) of composites obtained from z-stacked confocal micrographs, showing the distribution of dye in 3D (z+ direction is away from the substrate, XY is the imaging plane) Colour scale: blue (low intensity) to red (high intensity); black, no signal; White, detector saturation. (e,j,o) Line profiles (e) and intensity histograms (j,o) corresponding to the lines or regions shown on the orthogonal view images in (d,i,n) respectively. Scale bars, 15 μm (a); 10 μm (f); 25 μm (k); 20 μm (c,h,m).

Mentions: CaCO3 was precipitated in the presence of GREEN by combining equimolar solutions of CaCl2, and either Na2CO3 (5 or 25 mM) or NaHCO3 (3.5 mM). ACC is precipitated as the first phase under the former, but not under the latter conditions. Composite calcite crystals grown from [Ca2+]=[CO32−]=25 mM with [GREEN]/[Ca2+]=0.02 exhibited perfect rhombohedral morphologies and showed the highest fluorescence intensity towards the upper face (that is, that furthest from the glass substrate), indicating more efficient occlusion at later growth stages (Fig. 1a–e). This was confirmed from grey value line profiles, which showed that fluorescence intensity increased from the centre of the crystal towards the faces (Fig. 1e). Crystals additionally displayed a characteristic lower intensity cross spanning opposite vertices, where the CFM image presents a slice through the centre of the crystal.


3D visualization of additive occlusion and tunable full-spectrum fluorescence in calcite
GREEN/calcite host–guest composites.(a,f,k) Representative SEM micrographs of GREEN/calcite composite crystals precipitated under the conditions (a–e=[Ca2+]=[CO32−]=25 mM and [GREEN]=0.1 mM; f–j=[Ca2+]=[CO32−]=5 mM and [GREEN]=0.1 mM; and k–o=[Ca2+]=[HCO3−]=3.5 mM and [GREEN]=0.1 mM). (b,g,l) Three-dimensional (3D) representation of the morphologies of the crystals imaged in c,h,m, with approximate faces labelled, and the growth sectors coloured in green. The + and − labels denote obtuse and acute step morphologies, respectively. (c,h,m) Confocal fluorescence micrographs of composite crystals grown under the conditions. (d,i,n) Orthogonal views (XY, YZ and XZ) of composites obtained from z-stacked confocal micrographs, showing the distribution of dye in 3D (z+ direction is away from the substrate, XY is the imaging plane) Colour scale: blue (low intensity) to red (high intensity); black, no signal; White, detector saturation. (e,j,o) Line profiles (e) and intensity histograms (j,o) corresponding to the lines or regions shown on the orthogonal view images in (d,i,n) respectively. Scale bars, 15 μm (a); 10 μm (f); 25 μm (k); 20 μm (c,h,m).
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f1: GREEN/calcite host–guest composites.(a,f,k) Representative SEM micrographs of GREEN/calcite composite crystals precipitated under the conditions (a–e=[Ca2+]=[CO32−]=25 mM and [GREEN]=0.1 mM; f–j=[Ca2+]=[CO32−]=5 mM and [GREEN]=0.1 mM; and k–o=[Ca2+]=[HCO3−]=3.5 mM and [GREEN]=0.1 mM). (b,g,l) Three-dimensional (3D) representation of the morphologies of the crystals imaged in c,h,m, with approximate faces labelled, and the growth sectors coloured in green. The + and − labels denote obtuse and acute step morphologies, respectively. (c,h,m) Confocal fluorescence micrographs of composite crystals grown under the conditions. (d,i,n) Orthogonal views (XY, YZ and XZ) of composites obtained from z-stacked confocal micrographs, showing the distribution of dye in 3D (z+ direction is away from the substrate, XY is the imaging plane) Colour scale: blue (low intensity) to red (high intensity); black, no signal; White, detector saturation. (e,j,o) Line profiles (e) and intensity histograms (j,o) corresponding to the lines or regions shown on the orthogonal view images in (d,i,n) respectively. Scale bars, 15 μm (a); 10 μm (f); 25 μm (k); 20 μm (c,h,m).
Mentions: CaCO3 was precipitated in the presence of GREEN by combining equimolar solutions of CaCl2, and either Na2CO3 (5 or 25 mM) or NaHCO3 (3.5 mM). ACC is precipitated as the first phase under the former, but not under the latter conditions. Composite calcite crystals grown from [Ca2+]=[CO32−]=25 mM with [GREEN]/[Ca2+]=0.02 exhibited perfect rhombohedral morphologies and showed the highest fluorescence intensity towards the upper face (that is, that furthest from the glass substrate), indicating more efficient occlusion at later growth stages (Fig. 1a–e). This was confirmed from grey value line profiles, which showed that fluorescence intensity increased from the centre of the crystal towards the faces (Fig. 1e). Crystals additionally displayed a characteristic lower intensity cross spanning opposite vertices, where the CFM image presents a slice through the centre of the crystal.

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