Modern research in diagnostics is stimulating the development of highly luminescent and photostable biolabeling reagents for bioanalysis and cellular imaging, that can overcome limitations and drawbacks of organic fluorophores. Recently new kinds of biomarkers have been developed that are characterized by high photostability, signal enhancement, biocompatibility, easy handling and bioconjugation; among them, silica nanoparticles (NPs) loaded with fluorescent dyes are receiving an increasing attention. Here we report the synthesis of silica NPs loaded with cyanine dyes, that are really interesting for their high fluorescence yield and their structural versatility, that allows to obtain fluorescence in the Vis-NIR region where autofluorescence of biological samples is minimal. Their entrapment in a silica matrix should limit their conformational freedom degrees, resulting in an increase of their quantum yield, and prevent their interaction with O2. Hybrid cyanine-silica NPs were prepared in w/o microemulsion, via co-polymerization of TEOS (TetraEthoxySilane) and cyanine-APTS (AminoPropylTriethoxySilane). Cyanine loaded NPs were then characterised in term of morphology, size distribution, dispersion and surface properties by TEM, Dynamic Light Scattering and FT-IR spectroscopy. Photophysical properties were investigated with relation to sample form and dilution, in comparison with the dye in the molecular free form by UV-Vis absorption and emission spectroscopy, these latter augmented by lifetime measurements. Cyanine loaded NPs showed homogeneous spherical morphology and size distribution (=50±1 nm). The absence of any solvatochromic behaviour indicates that cyanine molecules were actually located within the silica matrix. FT-IR investigation showed the presence of surface free silanols, available for link with biomolecules of interest. The encapsulation inside the NPs resulted in a 10 folds increase of the photoemission lifetime of the fluorophore, as well as of the photoemission intensity per molecule. In addition, after prolonged irradiation the photoemission of hybrid NPs appeared quite stable (intensity loss: 10%), with respect to the fluorophores in the molecular free form (intensity loss: 50%).
Encapsulation of cyanine dyes in silica nanoparticles: effect on the photophysical properties
ALBERTO, Gabriele;MILETTO, IVANA;CAPUTO, Giuseppe;VISCARDI, Guido;MARTRA, Gianmario
2009-01-01
Abstract
Modern research in diagnostics is stimulating the development of highly luminescent and photostable biolabeling reagents for bioanalysis and cellular imaging, that can overcome limitations and drawbacks of organic fluorophores. Recently new kinds of biomarkers have been developed that are characterized by high photostability, signal enhancement, biocompatibility, easy handling and bioconjugation; among them, silica nanoparticles (NPs) loaded with fluorescent dyes are receiving an increasing attention. Here we report the synthesis of silica NPs loaded with cyanine dyes, that are really interesting for their high fluorescence yield and their structural versatility, that allows to obtain fluorescence in the Vis-NIR region where autofluorescence of biological samples is minimal. Their entrapment in a silica matrix should limit their conformational freedom degrees, resulting in an increase of their quantum yield, and prevent their interaction with O2. Hybrid cyanine-silica NPs were prepared in w/o microemulsion, via co-polymerization of TEOS (TetraEthoxySilane) and cyanine-APTS (AminoPropylTriethoxySilane). Cyanine loaded NPs were then characterised in term of morphology, size distribution, dispersion and surface properties by TEM, Dynamic Light Scattering and FT-IR spectroscopy. Photophysical properties were investigated with relation to sample form and dilution, in comparison with the dye in the molecular free form by UV-Vis absorption and emission spectroscopy, these latter augmented by lifetime measurements. Cyanine loaded NPs showed homogeneous spherical morphology and size distribution (=50±1 nm). The absence of any solvatochromic behaviour indicates that cyanine molecules were actually located within the silica matrix. FT-IR investigation showed the presence of surface free silanols, available for link with biomolecules of interest. The encapsulation inside the NPs resulted in a 10 folds increase of the photoemission lifetime of the fluorophore, as well as of the photoemission intensity per molecule. In addition, after prolonged irradiation the photoemission of hybrid NPs appeared quite stable (intensity loss: 10%), with respect to the fluorophores in the molecular free form (intensity loss: 50%).
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