Silica Nanobeads Research Articles

A novel ascorbic acid sensor based on the Fe3+/Fe2+ modulated photoluminescence of CdTe quantum dots@SiO2 nanobeads

In this paper, CdTe quantum dot (QD)@silica nanobeads were used as modulated photoluminescence (PL) sensors for the sensing of ascorbic acid in aqueous solution for the first time. The sensor was developed based on the different quenching effects of Fe(2+) and Fe(3+) on the PL intensity of the CdTe QD@ silica nanobeads. Firstly, the PL intensity of the CdTe QDs was quenched in the presence of Fe(3+). Although both Fe(2+) and Fe(3+) could quench the PL intensity of the CdTe QDs, the quenching efficiency were quite different for Fe(2+) and Fe(3+). The PL intensity of the CdTe QD@silica nanobeads can be quenched by about 15% after the addition of Fe(3+) (60 μmol L(-1)), while the PL intensity of the CdTe QD@silica nanobeads can be quenched about 49% after the addition of Fe(2+) (60 μmol L(-1)). Therefore, the PL intensity of the CdTe QD@silica nanobeads decreased significantly when Fe(3+) was reduced to Fe(2+) by ascorbic acid. To confirm the strategy of PL modulation in this sensing system, trace H2O2 was introduced to oxidize Fe(2+) to Fe(3+). As a result, the PL intensity of the CdTe QD@silica nanobeads was partly recovered. The proposed sensor could be used for ascorbic acid sensing in the concentration range of 3.33-400 μmol L(-1), with a detection limit (3σ) of 1.25 μmol L(-1) The feasibility of the proposed sensor for ascorbic acid determination in tablet samples was also studied, and satisfactory results were obtained.

A novel multifunctional nano-platform with enhanced anti-cancer and photoacoustic imaging modalities using gold-nanorod-filled silica nanobeads

The novel nano-seaurchin structure is characteristic of high-density and well-dispersed gold nanorods in one mesoporous silica nanobead. This nanoplatform provided increased photothermal stability, stable photoacoustic signal and highly efficient hyperthermia effect both in vitro and in vivo, indicating a powerful theranostic modality.

A new on-chip whole blood/plasma separator driven by asymmetric capillary forces

A new on-chip whole blood/plasma separator driven by asymmetric capillary forces, which are produced through a microchannel with sprayed nanobead multilayers, has been designed, fabricated and fully characterized. The silica nanobead multilayers revealing as superhydrophilic surfaces have been fabricated using a spray layer-by-layer (LbL) nano-assembly method. This new on-chip blood plasma separator has been targeted for a sample-to-answer (S-to-A) microfluidic lab-on-a-chip (LOC) toward point-of-care clinical testing (POCT). Effective plasma separation from undiluted whole blood was achieved through the microchannel which was composed of asymmetric superhydrophilic surfaces with a 10 mm hydrophobic patch. Blood cells were continuously accumulated over the hydrophobic patch while the blood plasma was able to flow over the patch. Therefore, the blood plasma was successfully separated from the whole blood throughout the accumulated blood cells which worked as a so-called 'self-built-in blood cell microfilter'. The separated plasma was approximately 102 nL from a single drop of 3 μL whole blood within 10 min, which is very suitable for single-use disposable POCT devices.

SUPPRESSION OF SIDELOBES IN SINGLE-PHOTON 4PI CONFOCAL MICROSCOPY BY FÖRSTER RESONANT ENERGY TRANSFER

Recently, we theoretically demonstrate that utilization of silica nanobeads co-doped with Cy3 and Cy5 molecules instead of single dye molecules as fluorescent labels can enable optical resolutions far beyond the diffraction-limit. Here, we show that by combining the 4Pi microscopy and the novel fluorescent label, it is possible to completely suppress the sidelobes in 4Pi focal spot and significantly enhance the optical resolution in the axial direction.

Real-time monitoring of DNA hybridization and melting processes using a fiber optic sensor

In this paper a fiber optic surface plasmon resonance (FO-SPR) sensor was used to analyze the melting process of DNA linked to silica nanoparticles. Real-time monitoring of a DNA melting process has rarely been studied using surface plasmon resonance (SPR), since most commercial SPR setups do not allow for dynamic and accurate temperature control above 50 °C. The FO-SPR sensor platform, with silica nanobead signal amplification, allows sensing inside a standard PCR thermocycler, which makes high resolution DNA melting curve analysis possible. This innovative combination was used to characterize the hybridization and melting events between DNA immobilized on the sensor surface and DNA probes on silica nanoparticles. At optimized hybridization conditions complementary DNA strands of different lengths could be distinguished. While the real-time FO-SPR analysis of DNA hybridization did not result in significant variances, the analysis of DNA melting determined the exact length of overlap and the matching Gibbs energy.

Effect of Surface Nanotopography on Immunoaffinity Cell Capture in Microfluidic Devices

Immunoaffinity microfluidic devices have recently become a popular choice to isolate specific cells for many applications. To increase cell capture efficiency, several groups have employed capture beds with nanotopography. However, no systematic study has been performed to quantitatively correlate surface nanopatterns with immunoaffinity cell immobilization. In this work, we controlled substrate topography by depositing close-packed arrays of silica nanobeads with uniform diameters ranging from 100 to 1150 nm onto flat glass. These surfaces were functionalized with a specific antibody and assembled as the base in microfluidic channels, which were then used to capture CD4+ T cells under continuous flow. It is observed that capture efficiency generally increases with nanoparticle size under low flow rate. At higher flow rates, cell capture efficiency becomes increasingly complex; it initially increases with the bead size then gradually decreases. Surprisingly, capture yield plummets atop depositions of some particle diameters. These dips likely stem from dynamic interactions between nanostructures on the substrate and cell membrane as indicated by roughness-insensitive cell capture after glutaraldehyde fixing. This systematic study of surface nanotopography and cell capture efficiency will help optimize the physical properties of microfluidic capture beds for cell isolation from biological fluids.

Deposition of anionic conjugated poly(phenylenevinylene) onto silica nanoparticles via electrostatic interactions — Assembly and single-particle spectroscopy

Fluorescent nanoparticles were prepared via adsorption of the conjugated polyelectrolyte poly[5-methoxy-2-(3-sulfopropoxy)-1,4-phenylenevinylene] (MPS-PPV) onto 50 and 100 nm aminosilane functionalized silica beads. The particles were investigated via ensemble and single-molecule or -particle spectroscopy techniques to quantify the effect of the silica bead core on the exciton migration efficiency within the polymer. Ensemble emission spectra and ensemble fluorescence quenching studies with methyl viologen are consistent with good exciton migration along the polymer in the polymer-coated bead. The silica nanobead scaffolding preserves the sensitivity of the free polymer and provides a controllable architecture that minimizes nonspecific interactions. Single-particle spectroscopy studies were conducted on particles immobilized onto the positively charged surface of glass cover slips. Particle immobilization enabled us to monitor the effect of oxygen scavenger solutions on individual particles by changing the surrounding solution. The intensity–time trajectories of individual beads provide a mechanism of signal transduction with potential applications in multiplexing studies. Hundreds of individual beads can be imaged in a rapid parallel fashion.

Lanthanopolyoxotungstates in silica nanoparticles: multi-wavelength photoluminescent core/shell materials

Photoluminescent lanthanopolyoxotungstate core/shell nanoparticles are prepared by the encapsulation of lanthanide-containing polyoxometalates (POMs) with amorphous silica shells. The preparation of morphological well-defined core/shell nanoparticles is achieved by the hydrolysis of tetraethoxysilane in the presence of POMs using a reverse microemulsion method. The POMs used are decatungstolanthanoates of [Ln(W5O18)2]9− type (Ln(III) = Eu, Gd and Tb). Photoluminescence studies show that there is efficient emission from the POM located inside the SiO2 shells, through excitation paths that involve O → Eu/Tb and O → W ligand-to-metal charge transfer. It is also shown that the excitation of the POM containing europium(III) may be tuned towards longer wavelengths via an antenna effect, by coordination of an organic ligand such as 3-hydroxypicolinate. The POM/SiO2 nanoparticles form stable suspensions in aqueous solution having the advantage of POM stabilization inside the core and the possibility of further surface grafting of chemical moieties via well known derivatization procedures for silica surfaces. These features together with the possibility of tuning the excitation wavelength by modifying the coordination sphere in the lanthanopolyoxometalate, make this strategy promising to develop a new class of optical bio-tags composed of silica nanobeads with multi-wavelength photoluminescent lanthanopolyoxometalate cores.

Large‐Area, Nanoimprint‐Assisted Microcontact Stripping for the Fabrication of Microarrays of Fouling/Nonfouling Nanostructures

Methods for the accurate positioning of nanometric beads on a substrate have been developed over a number of years, and range from serial atomic force microscopy (AFM) techniques for single-bead positioning to parallel techniques for the positioning of large populations of beads in monolayer or multilayer architectures, typically from a liquid suspension. For example, topographic cues have been used for bead-based protein array production, although in this case, there is a random distribution of beads within the topography. Bead patterning has also been achieved in capillaries using a micromolding in capillaries (MIMIC) technique. Line patterns with micrometer widths are possible with this technique, achieving good multilayer organization. For monolayer bead patterning at micrometer dimensions, electrostatic forces and similar electrostatic assemblies using nanoxerography, as well as patterning by selective chemical functionalization, by transfer of particles from a liquid–liquid interface, and by subtracting top–down processes, are possible. Recently, approaches to the micropatterning of nanodimensioned beads based on contact printing have appeared. Single-particle resolution has been achieved by directed assembly of the nanobeads on structured poly(dimethylsiloxane) (PDMS) templates. The beads are then transferred from the filled PDMS template to a substrate by microcontact printing. The beads’ surface composition during assembly must be tuned tomaximize the bead–surface interaction forces and to avoid strong adherence to the PDMS. Printing of dry nanobeads is, however, hard to realize. On the other hand, selective removal of beads from a surface using PDMSstructured molds has been achieved by lift-off and microcontact stripping. While the former needs a 3 h contact heat treatment to pattern close-packed silica nanobeads, the latter reports on a resolution limitation due to the crystal packing of the beads. Normally, in the reported contact-printing-based methods, the beads have to be loosely attached so that bead transfer or removal will not be inhibited. Here we present a contact-stripping method for micropatterning nanobead arrays, based on structured poly(methyl methacrylate) (PMMA) stamps and using a nanoimprinter apparatus, which allows careful control of the temperature and pressure during the contact stripping. Scheme 1 represents the patterning method. PMMA stamps, produced by nanoimprint lithography, are placed on the top of the nanobead-coated substrate with the structured parts of the stamp in contact with the beads inside the nanoimprinter chamber. Then pressure and temperature are applied for a few minutes. Afterwards, the stamps are carefully separated from the substrate. As a result, the particles in contact with the stamp are removed from the substrate, producing nanobead-patterned regions that reproduce the structure of the stamp. Microcontact

Effect of High Surface Curvature on the Main Phase Transition of Supported Phospholipid Bilayers on SiO2 Nanoparticles

Investigation of the physical properties of highly curved membranes is important in biology, for example, in fusion intermediates, and in pharmaceutical or chromatographic applications, where nanoscale features may affect substrate binding. However, vesicle fusion below 40 nm precludes study of this size regime. In this investigation, the effect of high surface curvature on the adsorption and morphology of phosphotidylcholine lipids with alkyl chain lengths of 14 (DMPC), 16 (DPPC), and 18 (DSPC) onto silica (SiO2) nanobeads was investigated by thermogravimetric analysis (TGA), high sensitivity nanocalorimetry, and vibrational spectroscopy. The SiO2 beads ranged in size from 5 to 100 nm. Stable supported bilayers were formed on all bead sizes by vesicle fusion of the parent MLVs at temperatures above the main phase transition temperature (T(m)) of the lipids. A downward shift in T(m), and a broadening (deltaT1/2) of the transition with respect to the parent MLVs, was observed for the 100 nm beads. With decreasing bead size, T(m) first decreased, but then increased. On the smallest bead size, whose dimensions were comparable to those of the adsorbed lipids, T(m)'s were higher than those of the parent MLVs. The increase in T(m) indicated a stiffening of the supported bilayer, which was confirmed by Raman spectroscopic data. Narrowing of the phase transition or the appearance of peak doublets occurred at the smaller bead sizes. The results were consistent with a model in which the high free volume and increased outer headgroup spacing of lipids on highly curved surfaces induced interdigitation in the supported lipids.

Circular dichroism analysis of penicillin G acylase covalently immobilized on silica nanoparticles

Circular dichroism (CD) was used to characterize the secondary structure of penicillin G acylase upon covalent immobilization on silica nanoparticles. Covalent immobilization was achieved by functionalizing the silica nanoparticles with glutardialdehyde and coupling to the free NH 2 groups of the enzyme (lysine and arginine side chains). The loading of the covalently bound enzyme was increased up to saturation, which was reached at 54.6 mg immobilized enzyme per g silica nanobeads. For structural characterization of the commercially available enzyme its exact molecular mass was determined by mass spectrometry in order to enable precise evaluation of the CD data. The fraction of secondary structure elements of the free and immobilized enzyme were estimated from the respective CD spectra using standard algorithms (CONTINLL, CDSSTR, SELCON3). The fractions obtained by the different algorithms for the free enzyme agreed well with one another and also with data from X-ray diffraction described in the literature. Interestingly, the secondary structure fractions found for the immobilized enzyme were very similar to the free enzyme and nearly constant over all experiments. These results indicate that even a loading of up to 55.8 mg/g (enzyme per silica nanoparticles) causes only slight structural changes. However, the specific activity determined by a kinetic assay decreased by around 60%, when increasing the loading from 14.9 to 55.8 mg/g. Because of the fact that we found no major changes in the secondary structure, diffusion limitation seems to be the main reason for the decline of the specific activity.

Luminescent Silica Nanobeads: Characterization and Evaluation as Efficient Cytoplasmatic Transporters for T-Lymphocytes

We report the fabrication and characterization of neutravidin-conjugated silica nanobeads doped with a ruthenium-complex luminophore and functionalized with antihuman CD3, antihuman CD28, and an acid-sensitive polymer. We observed that the nanobeads were readily delivered into Jurkat T leukemia cells by endocytosis, transported into lysosomes and subsequently into the cytoplasm as revealed by pH-sensitive luminescence. Since signs of cytotoxicity were not observed, the reported nanobeads could be an excellent and nontoxic building block for efficient intracellular transporters.

Biomedical Platforms Based on Composite Nanomaterials and Cellular Toxicity

Carbon nanotubes possess unique chemical, physical, optical, and magnetic properties, which make them suitable for many uses in industrial products and in the field of nanotechnology, including nanomedicine. We describe fluorescent nanocomposites for use in biosensors or nanoelectronics. Then we describe recent results on the issue of cytotoxicity of carbon nanotubes obtained in our labs. Silica nanoparticles have been widely used for biosensing and catalytic applications due to their large surface area-to-volume ratio, straightforward manufacture, and the compatibility of silica chemistry with covalent coupling of biomolecules. Carbon nanotubes-composite materials, such as those based on Carbon nanotubes bound to nanoparticles, are suitable, in order to tailor Carbon nanotubes properties for specific applications. We present a tunable synthesis of Multi Wall Carbon nanotubes-Silica nanoparticles. The control of the nanotube morphology and the bead size, coupled with the versatility of silica chemistry, makes these structures an excellent platform for the development of biosensors (optical, magnetic and catalytic applications). We describe the construction and characterization of supramolecular nanostructures consisting of ruthenium-complex luminophores, directly grafted onto short oxidized single-walled carbon nanotubes or physically entrapped in silica nanobeads, which had been covalently linked to short oxidized single-walled carbon nanotubes or hydrophobically adsorbed onto full-length multi-walled carbon nanotubes. These structures have been evaluated as potential electron-acceptor complexes for use in the fabrication of photovoltaic devices, and for their properties as fluorescent nanocomposites for use in biosensors or nanoelectronics. Finally, we compare the toxicity of pristine and oxidized Multi Walled Carbon nanotubes on human T cells - which would be among the first exposed cell types upon intravenous administration of Carbon nanotubes in therapeutic and diagnostic nanodevices. Our results suggest that carbon nanotubes indeed can be very toxic and induce massive loss of cell viability through programmed cell death at sufficiently high concentrations (>1ng/cell). The cytotoxicity of Carbon nanotubes does depend on many other factors than concentration, including their physical form, diameter, length, and the nature of attached molecules or nanomaterials: carbon black, for instance, is less toxic than pristine CNTs (what shows the relevance of structure and topology); oxidized CNTs are more toxic than pristine CNTs.

Synthesis and Characterization of Supramolecular Nanostructures of Carbon Nanotubes and Ruthenium-Complex Luminophores

We constructed and characterized supramolecular nanostructures consisting of ruthenium-complex luminophores, which were directly grafted onto short oxidized single-walled carbon nanotubes or physically entrapped in silica nanobeads, which had been covalently linked to short oxidized single-walled carbon nanotubes or hydrophobically adsorbed onto full-length multi-walled carbon nanotubes. These structures were evaluated as potential electron-acceptor complexes for use in the fabrication of photovoltaic devices, and for their properties as fluorescent nanocomposites for use in biosensors or nanoelectronics.

399. Solid Nanobeads Prevents Polycations from Entering the Nuclei and Enhanced Transfection Efficiency

Objective: Employment of polycations for gene delivery to treat human diseases remains in doubt as long as the potential for polycations to adversely interact with host genes exists, which is incurred from entering of polycations into nuclei during gene delivery. In this study, we address this issue by conjugating polymer vector- gene complexes to silica nanobeads (SNB) and evaluated the transfection efficacy of marker and therapeutic genes.

Silica Nanobeads-decorated Multi-walled Carbon Nanotubes by Vapor-phase Method

Abstract We report a new concise route to prepare carbon nanotube–silica nanobeads composites. The assembly of silica beads and nanotube by vapor-phase method make these structures an excellent platform for the development of biosensors, or for optical, magnetic and catalytic applications.

Control of the Colloidal Stability of Polymer‐Grafted‐Silica Nanoparticles Obtained by Atom Transfer Radical Polymerization

AbstractPolymer chains are grafted from silica nanobeads. The method consists in grafting first the initiator molecules on the silica surface. Then, the polymerization of styrene or n‐butyl methacrylate using Atom Transfer Radical Polymerization, is conducted. The nanoparticles are kept in solution during the whole process to avoid irreversible aggregation. The state of dispersion of the grafted silica nanoparticles is followed by Small Angle Neutron Scattering, as well as the quantity and the spatial organisation of the polymer. This is done during the functionalisation and the polymerization, but also after purification where free polymer chains are eliminated. This permits to reach a quantitative level of SANS analysis from these purified particles, which is compared to chemical data given by Size Exclusion Chromatography and Thermogravimetric analysis.

Covalent decoration of multi-walled carbon nanotubes with silica nanoparticles

We describe a novel tunable approach for the synthesis of carbon nanotube-silica nanobead composites. The control of nanotube morphology and bead size coupled with the versatility of silica chemistry makes these structures an excellent platform for the development of biosensors, or for optical, magnetic and catalytic applications.

Sub-micrometer silica spheres dissymmetrically decorated with gold nanoclusters

The elaboration of silica nanobeads where gold nanoclusters are strongly adsorbed onto the surface of only one hemisphere was performed by (i) immobilizing a monolayer of silica nanoparticles along the air/water or onto a glass substrate and (ii) reacting with colloidal gold nanoparticles or sputtered metallic gold. The dissymetrization routes are described, analyzed and compared.

Attaching Silica Nanoparticles from Suspension onto Surface Charge Patterns Generated by a Conductive Atomic Force Microscope Tip

A conductive atomic force microscope (AFM) tip acts as a nanopencilto write positive or negative charge patterns into a fluorocarbon film. Silica nanobeads (with a positive surface charge) can be attached to negative patterns by Coulombic interaction. While the resolution of the writing process is up to 100 nm, coagulation of the silica beads makes 1 μm a realistic minimum width for structures thus formed (see Figure and also cover).