Core-shell Silica Nanoparticles Research Articles

Assessment of uptake and toxicity of fluorescent silica nanoparticles in zebrafish ( Danio rerio) early life stages

In this study, we determined uptake and toxicity of fluorescent core-shell silica nanoparticles (FSNP) in early life stages of zebrafish. For this purpose fluorescent Ru@SiO 2 nanoparticles with average size of ∼200 nm encapsulating [Ru(bpy) 3] 2+Cl 2 dye (excitation wavelength λ exci = 488 nm), and Cy5.5@SiO 2 with average size of ∼60 nm ( λ exci = 700 nm) were synthesized. The FSNP were highly luminescent. Field emission SEM analysis showed monodispersed dual-shell Ru@SiO 2 nanoparticles of ∼200 nm size. Zebrafish embryos were exposed less than 6 h post-fertilization (hpf) to the ∼60 and ∼200 nm FSNP at concentrations between 0.0025 and 200 mg/L in 24-well plates for up to 96 hpf. The concentrations were analysed using an Fourier transform infra-red (FTIR) technique. Uptake of FSNP by embryos was monitored using transmission and confocal fluorescence microscopy. Toxicity was assessed by mortality, hatching time and success, and by morphological alterations. The ∼60 and ∼200 nm-sized FSNP and/or aggregates were adsorbed on the chorion of eggs. Uptake and translocation in embryos was not observed, but nanoparticle uptake not detectable by confocal microscopy may have occurred. Hatching time and hatching success were not affected. No mortality or deformities occurred. These nanoparticles and/or aggregates mainly accumulate on the chorion of embryos and exhibit no overt embryotoxicity.

The One-Step Pickering Emulsion Polymerization Route for Synthesizing Organic-Inorganic Nanocomposite Particles

Polystyrene-silica core-shell nanocomposite particles are successfully prepared via one-step Pickering emulsion polymerization. Possible mechanisms of Pickering emulsion polymerization are addressed in the synthesis of polystyrene-silica nanocomposite particles using 2,2-azobis(2-methyl-N-(2-hydroxyethyl)propionamide (VA-086) and potassium persulfate (KPS) as the initiator. Motivated by potential applications of “smart” composite particles in controlled drug delivery, the one-step Pickering emulsion polymerization route is further applied to synthesize polystyrene/poly(N-isopropylacrylamide) (PNIPAAm)-silica core-shell nanoparticles with N-isopropylacrylamide incorporated into the core as a co-monomer. The polystyrene/PNIPAAm-silica composite nanoparticles are temperature sensitive and can be taken up by human prostate cancer (PC3-PSMA) cells.

Sonochemical Synthesis of Networked Silica Shell with Reduced Microporosity on Titania Nanocores for Photocatalytic Activity Reduction

Silica shells with a high density of networks and reduced microporosity has been formed on titania nanocores via a sonochemical approach in the absence of ammonia as a hydrolyzing catalyst. The TiO 2 -silica core-shell nanoparticles were characterized by transmission electron microscopy, energy-dispersive X-ray analysis, Fourier transform infrared spectroscopy (FTIR), and microporosity measurements. The photocatalytic activity of coated titania was also reported. FTIR measurements showed that the silica shell was formed with a high density of networks through the formation of asymmetric Si-O-Si vibration and asymmetric Si-O-Si stretching vibration bonds. Moreover, the thickness and microporosity of the silica shell could be altered by controlling the sonochemical power and time parameters.

Functional Tomographic Fluorescence Imaging of pH Microenvironments in Microbial Biofilms by Use of Silica Nanoparticle Sensors

Attached bacterial communities can generate three-dimensional (3D) physicochemical gradients that create microenvironments where local conditions are substantially different from those in the surrounding solution. Given their ubiquity in nature and their impacts on issues ranging from water quality to human health, better tools for understanding biofilms and the gradients they create are needed. Here we demonstrate the use of functional tomographic imaging via confocal fluorescence microscopy of ratiometric core-shell silica nanoparticle sensors (C dot sensors) to study the morphology and temporal evolution of pH microenvironments in axenic Escherichia coli PHL628 and mixed-culture wastewater biofilms. Testing of 70-, 30-, and 10-nm-diameter sensor particles reveals a critical size for homogeneous biofilm staining, with only the 10-nm-diameter particles capable of successfully generating high-resolution maps of biofilm pH and distinct local heterogeneities. Our measurements revealed pH values that ranged from 5 to >7, confirming the heterogeneity of the pH profiles within these biofilms. pH was also analyzed following glucose addition to both suspended and attached cultures. In both cases, the pH became more acidic, likely due to glucose metabolism causing the release of tricarboxylic acid cycle acids and CO(2). These studies demonstrate that the combination of 3D functional fluorescence imaging with well-designed nanoparticle sensors provides a powerful tool for in situ characterization of chemical microenvironments in complex biofilms.

Site-Specific Labeling of Surface Proteins on Living Cells Using Genetically Encoded Peptides that Bind Fluorescent Nanoparticle Probes

We report a highly specific, robust, and generic method for noncovalent labeling of cellular proteins with highly fluorescent core-shell silica nanoparticles termed C dots. Our approach uses short genetically engineered peptides with affinity for silica (GEPS) that are site-specifically introduced at the termini or in loops of cellular proteins. Because GEPS are absent from native cell surface proteins, GEPS-tagged recombinant proteins can be selectively and rapidly labeled with fluorescent C dots. To demonstrate the versatility of our method, we targeted 30 nm C dots to two structurally distinct integral outer membrane proteins in Escherichia coli, FhuA and OmpX. Efficient labeling was achieved in 15 min or less and was observed to be highly sensitive and specific. This strategy provides a powerful technique, comparable to other chemical and biological labeling strategies, for efficient and quantitative investigation of protein function in live biological cells.

Fluorescent Biological Label for Recognizing Human Ovarian Tumor Cells Based on Fluorescent Nanoparticles

In this paper, we report a method for recognizing human ovarian tumor (HOT) cells using fluorescent biological label based on core-shell nanoparticles. The luminescent nanoparticles were synthesized with a water-in-oil (W/O) microemulsion technique. The fluorescent silica core-shell nanoparticles modified with anti-HER2 antibody using bifunctional cross-linker glutaraldehyde targeted the corresponding tumor antigen in the cell surface of the SKOV3 ovarian cancer cells. The specific immunoreactivity of antibody-nanoparticles with cells was characterized by laser scanning microscopy (LSM) and scanning electron microscope (SEM). The results showed that the method offered potential advantages of sensitivity and simplicity due to high binding efficiency between nanoparticles and cells and provided an alternative method for the detection of HOT.

Measurement of Plasma Volume using Nanoparticles in Mice

Plasma volume (PV) is an important pathogenic factor in hypertension and cardiovascular disease, and a target of infusion and diuretic therapies. However, PV is not commonly measured because available methods (distribution V of Evans Blue, radioactively labeled albumin or indocyanine green) are not well suited for routine hospital application. To measure PV we have used precisely sized and biologically inert core‐shell silica nanoparticles comprised of a dye‐rich core (Cy5), silica shell, and a coating of polyethylene glycol ("C dots"). Size‐gradated C dots (diameter in nm: 25, 20, 18, 14, 6 and 3) injected iv were not detected in the urine (fluorescence correlation spectroscopy) down to a size of 14 nm; in contrast, 6 and 3 nm C dots were rapidly excreted. To determine PV, C57 mice received a retro‐orbital injection of 25 nm C dots under brief isoflurane anesthesia. Plasma samples were taken from conscious mice after 10, 20, 30, and 60 min. Calculated distribution volume was not significantly different between time points suggesting retention of C dots in the vascular space. At 30 min PV averaged 1056 ± 81 μl (3.7 ± 0.1 % BW) in male and 843 ± 33 μl (3.1 ± 0.1 % BW) in female mice. After 24 h only 5.4 ± 1.7 % of injected particles was found in plasma. C dots may be a useful tool for assessing PV. Their range of applicability could be extended by using different particle sizes and encapsulated dyes with different fluorescent wavelengths.

Dye structure–optical property correlations in near-infrared fluorescent core-shell silica nanoparticles

In this paper we report on dye structure–optical property correlations for a range of near-infrared emitting (NIR, 650–900 nm) fluorescent dyes in a 9–14 nm diameter core-shell silica particle architecture (C dots), including Cy5, Alexa Fluor 700, DY730, Alexa Fluor 750, and DY780. For each dye an apparent per-dye enhancement in fluorescence is observed over free dye in aqueous solution ranging from 1.2× to 6.6×, highlighting the versatility of the silica encapsulation approach. For the Cy5 and DY730 dye/particle sample pairs photobleaching was undertaken and revealed that the particles photobleach slower than the dyes. For a particular NIR dye series with identical chemical backbone, DY730, DY731, DY732, and DY734, we demonstrate that with increasing number of sulfonated substituent groups the per-dye brightness enhancement decreases. Finally, we show that in special cases, like Cy5, brightness enhancement of dyes in dots over free dye may be a combination of effects from dye conjugation chemistry and immobilization in the silica matrix. These results provide powerful design criteria for next generation optical probes for applications ranging from bioimaging to security.

Silica Nanoparticle Architecture Determines Radiative Properties of Encapsulated Fluorophores

Silica nanoparticles with embedded fluorescent molecules are used in a variety of applications requiring the observation of single nanoprobes. We describe a class of fluorescent, core–shell silica nanoparticles with a radius of ∼15 nm, narrow particle size distribution, and controlled internal architecture. Particles covalently encapsulating multiple rhodamine molecules are over 20 times brighter than the single dye molecule in water. The photophysical behavior of rhodamine can be manipulated by small changes in the internal architecture of particles with otherwise similar composition, leading to 3-fold enhancement of quantum efficiency per dye with no observable energy transfer between neighboring dyes. This enhancement of quantum efficiency per dye is due to a uniform 2-fold enhancement in radiative rate and a variable reduction in nonradiative rate which varies inversely with the degree of rotational mobility of the dye allowed by the particle architecture. These results demonstrate a practical method ...

Preparation of iron boride–silica core–shell nanoparticles with soft ferromagneticproperties

A one-pot aqueous chemical synthesis for silica-passivated ferromagneticnanoparticles is presented. The average size of these particles is84 ± 20 nm. The x-ray and electron diffraction experiments revealed that the nanoparticles aremainly composed of polycrystalline iron boride. The broad x-ray diffraction peak leads toan average crystallite size of 1.8 nm, which is much smaller than the overall size of theparticles, and is consistent with the polycrystalline nature of the samples. Mössbauerspectroscopy and magnetization experiments were used to establish the roomtemperature magnetic properties as well as the chemical nature of the particles.Fe2B dominates the composition of the nanoparticles, having a hyperfine field broadlydistributed in the 10–33 T range. Alpha iron, the second ferromagnetic material identified inthe particles, amounts to 4.6% of the composition. Finally, a paramagnetic phaseaccounting for approximately 14.6% of the material of the particles was also detected.These nanoparticles contain a core with soft ferromagnetic properties surrounded by apassivating silica layer, and are suitable for magnetically targeted drug delivery andelectromagnetic induction heating applications.

Fluorescent core-shell silicananoparticles as tunable precursors: towards encoding and multifunctional nano-probes

Core-shell silica nanoparticles comprised of a RuBpy doped silica core and a Pas-DTPA doped silica shell were synthesized and post-functionalized with an encoding fluorescence combination and multiplex imaging function.

Intracellular delivery of core–shell fluorescent silica nanoparticles

Highly fluorescent core–shell silica nanoparticles made by the modified Stöber process (C dots) are promising as tools for sensing and imaging subcellular agents and structures but will only be useful if they can be easily delivered to the cytoplasm of the subject cells. This work shows that C dots can be electrostatically coated with cationic polymers, changing their surface charge and enabling them to escape from endosomes and enter the cytoplasm and nucleus. As an example of cellular delivery, we demonstrate that these particles can also be complexed with DNA and mediate and trace DNA delivery and gene expression.

Functionally modified core-shell silica nanoparticles by one-pot synthesis

In this work functionally modified silica nanoparticles were synthesized in base-catalyzed reaction of the elementary molecules: TEOS and vinyltriethoxysilane (VTEOS) using ethanol as the solvent. The main feature of the developed method is the addition of the modifier molecule, VTEOS, after appearance of the first primary particles in the reaction mixture. A core-shell structure was detected for the final particles having carbon-rich phase in the shell and silicon-rich phase in the core. The effect of TEOS/VTEOS molar ratio, solvent, reaction temperature and time was investigated on the particle size and morphology of the particles. The results showed that TEOS/VTEOS molar ratio of 90/10 and, reaction temperature of 40 °C using ethanol as the solvent yield the desired core-shell structure after 30 min of reaction time.

Core-shell silica nanoparticles as fluorescent labels for nanomedicine

Progress in biomedical imaging depends on the development of probes that combine low toxicity with high sensitivity, resolution, and stability. Toward that end, a new class of highly fluorescent core-shell silica nanoparticles with narrow size distributions and enhanced photostability, known as C dots, provide an appealing alternative to quantum dots. Here, C dots are evaluated with a particular emphasis on in-vivo applications in cancer biology. It is established that C dots are nontoxic at biologically relevant concentrations, and can be used in a broad range of imaging applications including intravital visualization of capillaries and macrophages, sentinel lymph node mapping, and peptide-mediated multicolor cell labeling for real-time imaging of tumor metastasis and tracking of injected bone marrow cells in mice. These results demonstrate that fluorescent core-shell silica nanoparticles represent a powerful novel imaging tool within the emerging field of nanomedicine.

Dispersion behavior of core–shell silica-polymer nanoparticles

Core–shell silica nanoparticles are superior in modifying surface wetting behavior, enhancing nucleation and growth in crystallization, improving dispersion of naked nanoparticles, and thus upgrading the overall properties of organic polymers. The dispersion behavior and morphology of monodisperse core–shell silica particles in several polymers including polyesters are reviewed and their potential applications are discussed.

Metal Enhanced Fluorescence Solution-based Sensing Platform 2: Fluorescent Core-Shell Ag@SiO2 Nanoballs

In this Rapid Communication, we present the development of monodisperse core-shell (silver core-silica shell) nanoparticles with various shell thicknesses featuring a fluorophore, subsequently named Metal-Enhanced Fluorescence (MEF) nanoballs. MEF nanoballs consist of a approximately 130 nm silver nanoparticle core, a silica shell with up to 35 nm thickness and fluorophores doped within the silica shell. Fluorescent nanobubbles where the silver core is removed by chemical etching are used as control samples to show the benefits of using silver nanoparticles, i.e, Metal-Enhanced Fluorescence. Finally, we demonstrate the broad potential biological applications of MEF nanoballs by employing near-infra red emitting probes (Rhodamine 800) within the silica shell, for potential applications in cellular imaging and solution-based sensing.

Functionalized fluorescent core-shell nanoparticles used as a fluorescent labels in fluoroimmunoassay for IL-6

Nanoparticle labels conjugated with biomolecules are used in a variety of different assay applications. In this paper, a sensitive fluoroimmunoassay for recombinant human interleukin-6 (IL-6) with the functionalized Rubpy-encapsulated fluorescent core-shell silica nanoparticles labeling technique has been proposed. IL-6 was measured based on the specific interaction between captured IL-6 antigen and functionalized fluorescent core-shell nanoparticles-labeled anti-IL-6 monoclonal antibody. The calibration graph for IL-6 was linear over the range 20–1250 pg ml −1 with a detection limit of 7 pg ml −1 (3 σ). The regression equation of the working curve is I F = 7.665 + 32.499 [IL-6] (ng ml −1) ( r = 0.9980). The relative standard deviation (R.S.D.) for 11 parallel measurements of 78 pg ml −1 IL-6 was 3.2%. Furthermore, the application of fluorescence microscopy imaging in the study of the antibody labeling and sandwich fluoroimmunoassay with the functionalized fluorescent core-shell silica nanoparticles was also explored. This proposed method has the advantage of showing the specificity of immunoassay and sensitivity of fluorescent nanoparticle labels technology. The results demonstrate that the method offers potential advantages of sensitivity, simplicity and reproducibility for the determination of IL-6, and is applicable to the determination of IL-6 in serum samples and enabling fluorescence microscopy imaging for the determination of IL-6.

Fluorescent Core—Shell Silica Nanoparticles: Towards “Lab on a Particle” Architectures for Nanobiotechnology

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Au–silica nanoparticles by “reverse” synthesis of cores in hollow silica shells

Core-silica shell nanoparticles were prepared in a "reverse" manner by nucleation and growth of Au cores within hollow silica nanospheres.

A novel sensitive staphylococcal enterotoxin C 1 fluoroimmunoassay based on functionalized fluorescent core-shell nanoparticle labels

A highly sensitive fluoroimmunoassay for the determination of staphylococcal enterotoxin C 1 (SEC 1) is proposed. It is based on the functionalized fluorescent core-shell nanoparticles as the labels coated with anti-SEC 1 monoclonal antibodies in “sandwich” fluoroimmunoassay. With the simple, inverse microemulsion polymerisation method, the functionalized fluorescent core-shell nanoparticles were prepared easily. The preparation process produces a silica shell on the surface of the Ru(bpy) 3Cl 2 (Rubpy) dye with one step cohydrolysis of tetraethylorthosilicate (TEOS), and the coupling agent (3-aminopropy1)triethoxysilane (APS) provided the amine groups that can be used for biological conjugation. The nanoparticles were then labeled with the anti-SEC 1 monoclonal antibodies and the antibody-labeled nanoparticles were successfully used for the determination of SEC 1. The calibration graph for SEC 1 was linear over the range 1.0–75.0 ng ml −1 with a detection limit of 0.3 ng ml −1. The regression equation of the working curve was I F = 24.583 + 0.6426[SEC 1] (ng ml −1) ( r = 0.9991). The relative standard deviation (RSD) for five parallel measurements of 25.0 ng ml −1 SEC 1 was 2.5%. Furthermore, the application of fluorescence microscopy imaging in the study of the antibody labeling and sandwich fluoroimmunoassay with the functionalized fluorescent core-shell silica nanoparticles was also explored. The results demonstrate that the method offers potential advantages of easily labeling to the antibody, sensitivity, simplicity and reproducibility for the determination of SEC 1 and is applicable to the determination of SEC 1 in real samples and enables fluorescence microscopy imaging for the determination of SEC 1.