Experimental and theoretical studies of the optimisation of fluorescence from near-infrared dye-doped silica nanoparticles

Biomedical Diagnostics Institute, National Centre for Sensor Research, School of Physical Sciences, Dublin City University, Glasnevin, Dublin 9, Ireland.
Analytical and Bioanalytical Chemistry (Impact Factor: 3.44). 11/2008; 393(4):1143-9. DOI: 10.1007/s00216-008-2418-9
Source: PubMed

ABSTRACT There is substantial interest in the development of near-infrared dye-doped nanoparticles (NPs) for a range of applications including immunocytochemistry, immunosorbent assays, flow cytometry, and DNA/protein microarray analysis. The main motivation for this work is the significant increase in NP fluorescence that may be obtained compared with a single dye label, for example Cy5. Dye-doped NPs were synthesised and a reduction in fluorescence as a function of dye concentration was correlated with the occurrence of homo-Förster resonance energy transfer (HFRET) in the NP. Using standard analytical expressions describing HFRET, we modelled the fluorescence of NPs as a function of dye loading. The results confirmed the occurrence of HFRET which arises from the small Stokes shift of near-infrared dyes and provided a simple method for predicting the optimum dye loading in NPs for maximum fluorescence. We used the inverse micelle method to prepare monodispersed silica NPs. The NPs were characterised using dynamic light scattering, UV spectroscopy, and transmission electron microscopy (TEM). The quantum efficiency of the dye inside the NPs, as a function of dye loading, was also determined. The fluorescent NPs were measured to be approximately 165 times brighter than the free dye, at an optimal loading of 2% (w/w). These experimental results were in good agreement with model predictions.

The change in nanoparticle fluorescence versus increased dye loading modelled using homo-Förster resonance energy transfer.

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Available from: Xavier Le Guével, Jul 01, 2014
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    • "Wiesner et al. have published several papers on the synthesis of far-red dye doped silica NPs, called C-DOTs, using a modified Stöber method which is discussed elsewhere [21] [22] [23]. With regard to the microemulsion method we have successfully incorporated a far-red dye (FR664) into silica NPs using a quaternary microemulsion method with Triton X surfactant [2]. However, the efficiency of dye loading was less than 20%, and loading with alternative far-red dyes was unsuccessful. "
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    ABSTRACT: Silica nanoparticles (NPs) doped with far-red fluorescent cyanine dyes, Cy5 and FR670, were prepared using the microemulsion method. The effects of nucleation pathway on dye loading and NP morphology were investigated using UV–Vis spectroscopy and transmission electron microscopy for different combinations of three surfactants, Triton® X-100, AOT and NP-5. Successful synthesis of monodispersed NPs with efficient dye loading was achieved using an intramicellar nucleation pathway combined with a negatively charged surfactant. For effective bioconjugation NPs were coated with a silica shell using either the microemulsion or the Stöber method. To maximise fluorescence intensity a series of NPs were doped with different amounts of dye ranging from 0.5 to 6% (w/w). At dye loadings of 0.5 and 0.25% (w/w) for Cy5 and FR670, respectively, NPs were 72 and 87 times more fluorescent than free dye labels. For Cy5 the change in fluorescence intensity with dye loading matched closely with a standard model for homo Förster resonance energy transfer (hFRET). A significant drop in fluorescence lifetime inside the NPs with increased dye loading was also observed and correlated with changes in energy transfer and quantum efficiency. Cy5 dye doped NPs were tested as biolabels in a fluorescence immunoassay to detect C-reactive protein, which is a recommended biomarker for cardiovascular disease. The NP label assay showed approximately an order of magnitude improvement in limit-of-detection when compared to a free dye assay.
    Sensors and Actuators B Chemical 12/2015; 221:470-479. DOI:10.1016/j.snb.2015.06.117 · 4.10 Impact Factor
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    • "All chemicals were obtained from Sigma Aldrich, (Sigma-Aldrich Corp., St. Louis, MO) unless otherwise stated. Silica nanoparticles (φ=74 nm) containing fluorescein (3 (w/w)) and synthetic premiR-34a (0.1 (w/w)), or a scrambled miR-negative control (0.1 (w/w)) were prepared using a microemulsion method [71]. The mechanism for formation of silica nanoparticles, outlined in Figure S1C, involves hydrolysis and condensation of a silica precursor (tetraethylorthosilicate). The proposed mechanism of drug delivery is dissolution of the nanoparticle and release of the dye under physiological conditions via hydrolysis of the silica network. "
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    ABSTRACT: Neuroblastoma is one of the most challenging malignancies of childhood, being associated with the highest death rate in paediatric oncology, underlining the need for novel therapeutic approaches. Typically, patients with high risk disease undergo an initial remission in response to treatment, followed by disease recurrence that has become refractory to further treatment. Here, we demonstrate the first silica nanoparticle-based targeted delivery of a tumor suppressive, pro-apoptotic microRNA, miR-34a, to neuroblastoma tumors in a murine orthotopic xenograft model. These tumors express high levels of the cell surface antigen disialoganglioside GD2 (GD(2)), providing a target for tumor-specific delivery. Nanoparticles encapsulating miR-34a and conjugated to a GD(2) antibody facilitated tumor-specific delivery following systemic administration into tumor bearing mice, resulted in significantly decreased tumor growth, increased apoptosis and a reduction in vascularisation. We further demonstrate a novel, multi-step molecular mechanism by which miR-34a leads to increased levels of the tissue inhibitor metallopeptidase 2 precursor (TIMP2) protein, accounting for the highly reduced vascularisation noted in miR-34a-treated tumors. These novel findings highlight the potential of anti-GD(2)-nanoparticle-mediated targeted delivery of miR-34a for both the treatment of GD(2)-expressing tumors, and as a basic discovery tool for elucidating biological effects of novel miRNAs on tumor growth.
    PLoS ONE 05/2012; 7(5):e38129. DOI:10.1371/journal.pone.0038129 · 3.23 Impact Factor
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    • "Use of a higher dye concentration, however, led to a bathochromic shift of the emission spectra due to re-absorption and a decrease in absolute fluorescence quantum yield of the bound dyes (Table 3). This is ascribed to fluorescence quenching dye-dye interactions (Schobel et al. 1999; Johansson and Cook 2003; Nooney et al. 2009), the size of which depends on the distance between the attached fluorophores and thus, on dye labelling density. The formation of nonfluorescent aggregates on the SNP surface is indicated by changes in the absorption spectra of the highly labelled SNPs (Figure 3, right, increase in the shorter wavelength peak of the dye´s main absorption band). "
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    ABSTRACT: Current and future developments in the emerging field of nanobiotechnology are closely linked to the rational design of novel fluorescent nanomaterials, e. g. for biosensing and imaging applications. Here, the synthesis of bright near infrared (NIR)-emissive nanoparticles based on the grafting of silica nanoparticles (SNPs) with 3-aminopropyl triethoxysilane (APTES) followed by covalent attachment of Alexa dyes and their subsequent shielding by an additional silica shell are presented. These nanoparticles were investigated by dynamic light scattering (DLS), transmission electron microscopy (TEM) and fluorescence spectroscopy. TEM studies revealed the monodispersity of the initially prepared and fluorophore-labelled silica particles and the subsequent formation of raspberry-like structures after addition of a silica precursor. Measurements of absolute fluorescence quantum yields of these scattering particle suspensions with an integrating sphere setup demonstrated the influence of dye labelling density-dependent fluorophore aggregation on the signaling behaviour of such nanoparticles.
    Journal of Nanoparticle Research 01/2011; 14(2). DOI:10.1007/s11051-011-0680-9 · 2.18 Impact Factor
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