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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.


Excitation and emission spectra of aqueous solutions of IR 806 and silica nanoparticles doped with IR 806 (3c, 4c).
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Figure 7: Excitation and emission spectra of aqueous solutions of IR 806 and silica nanoparticles doped with IR 806 (3c, 4c).

Mentions: The results are presented in Figure 7, and show three excitation peaks upon emission at 806 nm. The main excitation peak was observed as a sharp peak at 824 nm. Especially noteworthy was the observation of significant overlapping secondary peaks at 702 and 746 nm, equivalent in intensity. The emission peak was recorded at 837 nm. A comparison of the excitation and emission spectra measured for silica-based samples 1c, 2c, 3c and 4c gave various results. Fluorescence was measured but not recorded for samples 1c and 2c indicating the non-encapsulation of the IR 806 dye under those conditions. Most probably, the encapsulation's failures imply that the kinetic rate of hydrolysis of the TEOS prevent from ideal encapsulation conditions. Slow hydrolysis to produce the silica network can emphasise the exclusion of the molecule as well as an enhancement of the porosity of the silica network of the nanoparticles [55]. Hence, two straightforward explanations come to mind, either the dye is excluded during the growth of the silica matrix of the nanoparticle, or it is first encapsulated then released during the different washing steps due to the porosity of the silica network. Opposite results were observed for experiments 3c and 4c which encapsulations were successful. Fluorescent spectra of sample 3c are illustrated in Figure 5. The single excitation peak and emission peak were recorded at 827 and 839 nm, respectively. The slight bathochromic shift observed (2-3 nm) suggests an effect/influence of the confined IR 806 dye into the silica nanoparticles. Fluorescent spectra of sample 4c are also shown in Figure 7. Important hypsochromic shifts are observed as well as disappearance of the main sharp excitation peak occurring at 824 nm. The single excitation peak was recorded at 660 nm and the corresponding emission peak was observed at 743 nm. The encapsulation of IR 806 in the silica network of the nanoparticles tends to totally quench the low energy transition, therefore exhibiting only the secondary or high energy transition. Measurements of fluorescence of an aqueous solution of IR 806 did not exhibit luminescence at 743 nm upon excitation at 660 nm. The induced shift effect was observed and resulted from the confinement of the fluorescent dye within the silica particle, when prepared with TMOS. Subsequently, it is reasonable to assume that the interactions of the hydroxyl groups of the silica network with the IR 806 fluorescent dye tend to block preferably the radiative transitions at 806 nm than those at 743 nm. Furthermore, the successful encapsulation can result in the use of TMOS instead of TEOS which possess a faster rate of hydrolysis and build a denser silica network embedding more efficiently the IR 806 dye as explained in the paragraph above.


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)

Excitation and emission spectra of aqueous solutions of IR 806 and silica nanoparticles doped with IR 806 (3c, 4c).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 7: Excitation and emission spectra of aqueous solutions of IR 806 and silica nanoparticles doped with IR 806 (3c, 4c).
Mentions: The results are presented in Figure 7, and show three excitation peaks upon emission at 806 nm. The main excitation peak was observed as a sharp peak at 824 nm. Especially noteworthy was the observation of significant overlapping secondary peaks at 702 and 746 nm, equivalent in intensity. The emission peak was recorded at 837 nm. A comparison of the excitation and emission spectra measured for silica-based samples 1c, 2c, 3c and 4c gave various results. Fluorescence was measured but not recorded for samples 1c and 2c indicating the non-encapsulation of the IR 806 dye under those conditions. Most probably, the encapsulation's failures imply that the kinetic rate of hydrolysis of the TEOS prevent from ideal encapsulation conditions. Slow hydrolysis to produce the silica network can emphasise the exclusion of the molecule as well as an enhancement of the porosity of the silica network of the nanoparticles [55]. Hence, two straightforward explanations come to mind, either the dye is excluded during the growth of the silica matrix of the nanoparticle, or it is first encapsulated then released during the different washing steps due to the porosity of the silica network. Opposite results were observed for experiments 3c and 4c which encapsulations were successful. Fluorescent spectra of sample 3c are illustrated in Figure 5. The single excitation peak and emission peak were recorded at 827 and 839 nm, respectively. The slight bathochromic shift observed (2-3 nm) suggests an effect/influence of the confined IR 806 dye into the silica nanoparticles. Fluorescent spectra of sample 4c are also shown in Figure 7. Important hypsochromic shifts are observed as well as disappearance of the main sharp excitation peak occurring at 824 nm. The single excitation peak was recorded at 660 nm and the corresponding emission peak was observed at 743 nm. The encapsulation of IR 806 in the silica network of the nanoparticles tends to totally quench the low energy transition, therefore exhibiting only the secondary or high energy transition. Measurements of fluorescence of an aqueous solution of IR 806 did not exhibit luminescence at 743 nm upon excitation at 660 nm. The induced shift effect was observed and resulted from the confinement of the fluorescent dye within the silica particle, when prepared with TMOS. Subsequently, it is reasonable to assume that the interactions of the hydroxyl groups of the silica network with the IR 806 fluorescent dye tend to block preferably the radiative transitions at 806 nm than those at 743 nm. Furthermore, the successful encapsulation can result in the use of TMOS instead of TEOS which possess a faster rate of hydrolysis and build a denser silica network embedding more efficiently the IR 806 dye as explained in the paragraph above.

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.