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A comparative study of non-covalent encapsulation methods for organic dyes into silica nanoparticles.

Auger A, Samuel J, Poncelet O, Raccurt O - Nanoscale Res Lett (2011)

Bottom Line: Nevertheless, the behaviour and effect of such luminescent molecules appear to have been much less studied and may possibly prevent the encapsulation process from occurring.Mainly, the photophysical characteristics of the dyes are retained upon their encapsulation into the silica matrix, leading to fluorescent silica nanoparticles.This feature article surveys recent research progress on the fabrication strategies of these dye-doped silica nanoparticles.

View Article: PubMed Central - HTML - PubMed

Affiliation: CEA Grenoble, Department of Nano Materials, NanoChemistry and NanoSafety Laboratory (DRT/LITEN/DTNM/LCSN), 17 rue des Martyrs, 38054 Grenoble Cedex 9, France. aurelien.auger@cea.fr.

ABSTRACT
Numerous luminophores may be encapsulated into silica nanoparticles (< 100 nm) using the reverse microemulsion process. Nevertheless, the behaviour and effect of such luminescent molecules appear to have been much less studied and may possibly prevent the encapsulation process from occurring. Such nanospheres represent attractive nanoplatforms for the development of biotargeted biocompatible luminescent tracers. Physical and chemical properties of the encapsulated molecules may be affected by the nanomatrix. This study examines the synthesis of different types of dispersed silica nanoparticles, the ability of the selected luminophores towards incorporation into the silica matrix of those nanoobjects as well as the photophysical properties of the produced dye-doped silica nanoparticles. The nanoparticles present mean diameters between 40 and 60 nm as shown by TEM analysis. Mainly, the photophysical characteristics of the dyes are retained upon their encapsulation into the silica matrix, leading to fluorescent silica nanoparticles. This feature article surveys recent research progress on the fabrication strategies of these dye-doped silica nanoparticles.

No MeSH data available.


Transmittance spectra of aqueous solutions of PABI and silica nanoparticles doped with PABI (1a, 2a, 3a and 4a).
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Figure 5: Transmittance spectra of aqueous solutions of PABI and silica nanoparticles doped with PABI (1a, 2a, 3a and 4a).

Mentions: The transmission spectra of pure PABI dye and PABI nanoparticles were measured in aqueous solution (Figure 5). Since the PABI dye is not fluorescent, the encapsulation phenomenon could be checked by transmission measurements. The pure dye solution showed three typical absorption peaks characteristic of the aromatic macrocyclic π-electron of phthalocyanine dyes. Absorption maxima were recorded at 342 nm (B-band), 612 nm (vibrational band) and 668 nm (Q-band). The transmission spectra for the pure PABI and the samples 1a, 2a, 3a and 4a displayed almost the same profile in aqueous solution, though there was only a very slight red-shift (1-2 nm) for their absorbance maxima when compared to each PABI nanoparticles prepared respectively. Those results indicate that the four methods of encapsulation used were successful. The PABI dye seemed to be proper towards encapsulation conditions. Once embedded into the silica nanoparticles (samples 1a, 2a, 3a and 4a), the flat and rigid aromatic core of the phthalocyanine derivative can no longer escape, and remain well trapped within the silica network. Furthermore, phthalocyanine dyes are well-known to aggregate and generate π-stacking, and such phenomenon could emphasise the stability of those dyes towards encapsulation. The ordering of the π-stacking of the PABI molecules can favour their insertion into the silica network. Also, the π-stacking could be generated into the micelle, enhancing the rigidity of the organically bulk structure and therefore favouring the encapsulation process. Additionally, the interactions between the nitrogen atoms of the four imino bridges of the phthalocyanine aromatic core of the PABI, and the hanging hydroxyl of the silica core-shell facilitate further the encapsulation. The interactions of the dye to encapsulate with the silica network of the nanoparticles added to the rigidity of its aromatic core confer excellent conditions towards encapsulation. Prior to the results obtained with PABI, such conditions have been reported for the encapsulation of fluorescein 1 h and rhodamine B 1g. Similarly, those molecules possess reasonably flat and rigid aromatic cores, in part due to the conjugated system, emphasising the aromaticity and the stability of those dyes, and also due to the spiro centre contained in the structure of the fluorescein, and the lack of freedom towards the vertical bond in the molecule of rhodamine B, between the oxo-anthracenyl analogue core and the vertical ortho-carboxyphenyl substituent. The latest could introduce atropisomerism, exhibiting blocked isomers leading to rigid structures lacking of three-dimensional freedom, and therefore facilitating the encapsulation process.


A comparative study of non-covalent encapsulation methods for organic dyes into silica nanoparticles.

Auger A, Samuel J, Poncelet O, Raccurt O - Nanoscale Res Lett (2011)

Transmittance spectra of aqueous solutions of PABI and silica nanoparticles doped with PABI (1a, 2a, 3a and 4a).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211415&req=5

Figure 5: Transmittance spectra of aqueous solutions of PABI and silica nanoparticles doped with PABI (1a, 2a, 3a and 4a).
Mentions: The transmission spectra of pure PABI dye and PABI nanoparticles were measured in aqueous solution (Figure 5). Since the PABI dye is not fluorescent, the encapsulation phenomenon could be checked by transmission measurements. The pure dye solution showed three typical absorption peaks characteristic of the aromatic macrocyclic π-electron of phthalocyanine dyes. Absorption maxima were recorded at 342 nm (B-band), 612 nm (vibrational band) and 668 nm (Q-band). The transmission spectra for the pure PABI and the samples 1a, 2a, 3a and 4a displayed almost the same profile in aqueous solution, though there was only a very slight red-shift (1-2 nm) for their absorbance maxima when compared to each PABI nanoparticles prepared respectively. Those results indicate that the four methods of encapsulation used were successful. The PABI dye seemed to be proper towards encapsulation conditions. Once embedded into the silica nanoparticles (samples 1a, 2a, 3a and 4a), the flat and rigid aromatic core of the phthalocyanine derivative can no longer escape, and remain well trapped within the silica network. Furthermore, phthalocyanine dyes are well-known to aggregate and generate π-stacking, and such phenomenon could emphasise the stability of those dyes towards encapsulation. The ordering of the π-stacking of the PABI molecules can favour their insertion into the silica network. Also, the π-stacking could be generated into the micelle, enhancing the rigidity of the organically bulk structure and therefore favouring the encapsulation process. Additionally, the interactions between the nitrogen atoms of the four imino bridges of the phthalocyanine aromatic core of the PABI, and the hanging hydroxyl of the silica core-shell facilitate further the encapsulation. The interactions of the dye to encapsulate with the silica network of the nanoparticles added to the rigidity of its aromatic core confer excellent conditions towards encapsulation. Prior to the results obtained with PABI, such conditions have been reported for the encapsulation of fluorescein 1 h and rhodamine B 1g. Similarly, those molecules possess reasonably flat and rigid aromatic cores, in part due to the conjugated system, emphasising the aromaticity and the stability of those dyes, and also due to the spiro centre contained in the structure of the fluorescein, and the lack of freedom towards the vertical bond in the molecule of rhodamine B, between the oxo-anthracenyl analogue core and the vertical ortho-carboxyphenyl substituent. The latest could introduce atropisomerism, exhibiting blocked isomers leading to rigid structures lacking of three-dimensional freedom, and therefore facilitating the encapsulation process.

Bottom Line: Nevertheless, the behaviour and effect of such luminescent molecules appear to have been much less studied and may possibly prevent the encapsulation process from occurring.Mainly, the photophysical characteristics of the dyes are retained upon their encapsulation into the silica matrix, leading to fluorescent silica nanoparticles.This feature article surveys recent research progress on the fabrication strategies of these dye-doped silica nanoparticles.

View Article: PubMed Central - HTML - PubMed

Affiliation: CEA Grenoble, Department of Nano Materials, NanoChemistry and NanoSafety Laboratory (DRT/LITEN/DTNM/LCSN), 17 rue des Martyrs, 38054 Grenoble Cedex 9, France. aurelien.auger@cea.fr.

ABSTRACT
Numerous luminophores may be encapsulated into silica nanoparticles (< 100 nm) using the reverse microemulsion process. Nevertheless, the behaviour and effect of such luminescent molecules appear to have been much less studied and may possibly prevent the encapsulation process from occurring. Such nanospheres represent attractive nanoplatforms for the development of biotargeted biocompatible luminescent tracers. Physical and chemical properties of the encapsulated molecules may be affected by the nanomatrix. This study examines the synthesis of different types of dispersed silica nanoparticles, the ability of the selected luminophores towards incorporation into the silica matrix of those nanoobjects as well as the photophysical properties of the produced dye-doped silica nanoparticles. The nanoparticles present mean diameters between 40 and 60 nm as shown by TEM analysis. Mainly, the photophysical characteristics of the dyes are retained upon their encapsulation into the silica matrix, leading to fluorescent silica nanoparticles. This feature article surveys recent research progress on the fabrication strategies of these dye-doped silica nanoparticles.

No MeSH data available.