Submicron Silica Research Articles

Comparing novel small-angle x-ray scattering approaches for absolute size and number concentration measurements of spherical SiO2 particles to established methods

Biomedical analytical applications, as well as the industrial production of high-quality nano- and sub-micrometre particles, require accurate methods to quantify the absolute number concentration of particles. In this context, small-angle x-ray scattering (SAXS) is a powerful tool to determine the particle size and concentration traceable to the Système international d’unités (SI). Therefore, absolute measurements of the scattering cross-section must be performed, which require precise knowledge of all experimental parameters, such as the electron density of solvent and particles, whereas the latter is often unknown. Within the present study, novel SAXS-based approaches to determine the size distribution, density and number concentrations of sub-micron spherical silica particles with narrow size distributions and mean diameters between 160 nm and 430 nm are presented. For the first-time traceable density and number concentration measurements of silica particles are presented and current challenges in SAXS measurements such as beam-smearing, poorly known electron densities and moderately polydisperse samples are addressed. In addition, and for comparison purpose, atomic force microscopy has been used for traceable measurements of the size distribution and single particle inductively coupled plasma mass spectrometry with the dynamic mass flow approach for the accurate quantification of the number concentrations of silica particles. The possibilities and limitations of the current approaches are critically discussed in this study.

Structural performance and durability assessment of ultrafine powdered concrete in modern buildings

Abstract This paper investigates the impact of various ultrafine powders on the flow characteristics and mechanical properties of concrete, with the aim of enhancing its overall performance. Examine the compressive and flexural strengths of cement, establish distinct matching ratios, and clarify the actual mixing quantity of silica fume and ultrafine powder. Analyze the durability of concrete structures and propose causes for carbonation and formation of concrete. Obtain the durability evaluation indexes, propose the variable weight fuzzy comprehensive judgment method, and establish the durability evaluation system for ultrafine powder concrete buildings. When the on-site test results for reinforcement corrosion, concrete strength, carbonation depth, cracks, and damage degree are added together, the values of each assessment vector of the fuzzy comprehensive evaluation are found. This lets us figure out the bridge’s durability grade. The highest compressive degree was achieved by both ultrafine silica-aluminum material and ultrafine mineral fishery powder at a 20% dosage. The submicron silica material achieved the highest compressive strength with a 40% dosage. In the test and analysis of the ultrafine powder concrete bridge building structure, the fuzzy comprehensive judgment grade is III. That is, there is a certain degree of damage state, and measures must be taken, which is consistent with the field test results.

Large scale synthesis of mesoporous and nonporous silica submicron particles via polymer‐derived ceramic method

AbstractMesoporous silica particles (MSPs) are highly important in applications like H2 storage, catalysis/biocatalysis, adsorption, separation, and particularly in biomedical applications. The typical methods for producing MSPs are fast self‐assembly, soft and hard templating, and the modified Stöber method. These approaches have drawbacks like high cost, being time‐consuming, and low scale. Herein, as a novel strategy, a polymer‐derived ceramic method for large‐scale production of mesoporous and dense silica submicron particles with high yield and low cost is presented. This method requires commercial silicone resin, polydimethylsiloxane, as the main precursor of silica. However, this technique did not show high control over the size and surface area compared with the typical methods of MSPs synthesis but is definitely a significant step toward the large‐scale synthesis of MSPs.

Novel zone elution mode in coiled tube field-flow fractionation for online separation and characterization of environmental submicron particles.

Coiled tube field-flow fractionation (CTFFF) is currently applied to environmental and material studies. In the present work, a novel zone elution mode in CTFFF has been proposed and developed. Zone elution mode is based on the separation of particles by stepwise decreasing the flow rate of the carrier fluid and their subsequent elution at a constant flow rate. The fractionation parameters were optimized using a mixture of standard silica submicron particles (150, 390, and 900nm). Taking samples of volcanic ash as examples, it has been demonstrated that zone elution mode can be successfully used for the fractionation of environmental nano- and submicron particles. For the first time, CTFFF was coupled online with a dynamic light scattering detector for the size characterization of eluted particles. Zone elution in CTFFF can serve for the further development of hyphenated techniques enabling efficient fractionation and size/elemental characterization of environmental particles in nano- and submicrometric size ranges.

Quantitative Elasticity Mapping of Submicron Silica Hollow Particles by PeakForce QNM AFM Mode.

Silica hollow spheres with a diameter of 100-300 nm and a shell thickness of 8±2 nm were synthesized using a self-templating amphiphilic polymeric precursor, i.e., poly(ethylene glycol)-substituted hyperbranched polyethoxysiloxane. Their elastic properties were addressed with a high-frequency AFM indentation method based on the PeakForce QNM (quantitative nanomechanical mapping) mode enabling simultaneous visualization of the surface morphology and high-resolution mapping of the mechanical properties. The factors affecting the accuracy of the mechanical measurements such as a local slope of the particle surface, deformation of the silica hollow particles by a solid substrate, shell thickness variation, and applied force range were analysed. The Young's modulus of the shell material was evaluated as E=26±7 GPa independent of the applied force in the elastic regime of deformations. Beyond the elastic regime, the buckling instability was observed revealing a non-linear force-deformation response with a hysteresis between the loading and unloading force-distance curves and irreversible deformation of the shell at high applied forces. Thus, it was demonstrated that PeakForce QNM mode can be used for quantitative measurements of the elastic properties of submicon-sized silica hollow particles with nano-size shell thickness, as well as for estimation of the buckling behaviour beyond the elastic regime of shell deformations.

Absolute Counting Method with Multiplexing Capability for Estimating the Number Concentration of Nanoparticles Using Anisotropically Collapsed Gels.

Number concentration─the number of nanoparticles in a given volume─is an important characteristic of any nanoparticle dispersion. However, its estimation for small nanoparticles (∼30 nm) is generally challenging. We introduce an absolute and widely applicable method for analyzing aqueous dispersions of nanoparticles. An innovative immobilization of nanomaterials in the anisotropically collapsed agarose gel is pioneered, followed by optical microscopy and nanoparticle counting. The number of counted nanoparticles is inherently coupled with sampled volume (517 pL) and translates to the number concentration. Photon-upconversion, fluorescence, bright-field, and dark-field microscopy techniques have been proven applicable and used for imaging lanthanide-doped photon-upconversion nanoparticles, their bioconjugates with antibodies, silica dye-doped fluorescent nanoparticles, quantum dots, and pure silica submicron particles. The precision and linearity were characterized by constructing a dilution series of photon-upconversion nanoparticles. The limit of detection was 2.0 × 106 mL-1, and the working range was from 4.4 × 107 to 2.2 × 1010 mL-1. The quantification of nanoparticle clusters was achieved by a thorough analysis of the micrographs. The accuracy was confirmed using gravimetric analysis and transmission electron microscopy as a reference. Multiplexed detection of two nanoparticle types in a mixed dispersion was feasibly demonstrated. The low thickness of the collapsed gel (<1 μm) supported extremely sensitive imaging. This was proven by imaging Tm3+-doped photon-upconversion nanoparticles (17 nm hydrodynamic diameter) with a nanoparticle emission rate of only ∼900 photons/s at a wavelength of 800 nm (excitation wavelength 976 nm).

Design of an Artificial Opal/Photonic Crystal Interface for Alcohol Intoxication Assessment: Capillary Condensation in Pores and Photonic Materials Work Together

Alcohol intoxication has a dangerous effect on human health and is often associated with a risk of catastrophic injuries and alcohol-related crimes. A demand to address this problem adheres to the design of new sensor systems for the real-time monitoring of exhaled breath. We introduce a new sensor system based on a porous hydrophilic layer of submicron silica particles (SiO2 SMPs) placed on a one-dimensional photonic crystal made of Ta2O5/SiO2 dielectric layers whose operation relies on detecting changes in the position of surface wave resonance during capillary condensation in pores. To make the active layer of SiO2 SMPs, we examine the influence of electrostatic interactions of media, particles, and the surface of the crystal influenced by buoyancy, gravity force, and Stokes drag force in the frame of the dip-coating preparation method. We evaluate the sensing performance toward biomarkers such as acetone, ammonia, ethanol, and isopropanol and test sensor system capabilities for alcohol intoxication assessment. We have found this sensor to respond to all tested analytes in a broad range of concentrations. By processing the sensor signals by principal component analysis, we selectively determined the analytes. We demonstrated the excellent performance of our device for alcohol intoxication assessment in real-time.

Fluorescent molecularly imprinted polymer particles for glyphosate detection using phase transfer agents

In this work, molecular imprinting was combined with direct fluorescence detection of the pesticide Glyphosate (GPS). Firstly, the solubility of highly polar GPS in organic solvents was improved by using lipophilic tetrabutylammonium (TBA+) and tetrahexylammonium (THA+) counterions. Secondly, to achieve fluorescence detection, a fluorescent crosslinker containing urea-binding motifs was used as a probe for GPS-TBA and GPS-THA salts in chloroform, generating stable complexes through hydrogen bond formation. The GPS/fluorescent dye complexes were imprinted into 2–3 nm fluorescent molecularly imprinted polymer (MIP) shells on the surface of sub-micron silica particles using chloroform as porogen. Thus, the MIP binding behavior could be easily evaluated by fluorescence titrations in suspension to monitor the spectral changes upon addition of the GPS analytes. While MIPs prepared with GPS-TBA and GPS-THA both displayed satisfactory imprinting following titration with the corresponding analytes in chloroform, GPS-THA MIPs displayed better selectivity against competing molecules. Moreover, the THA+ counterion was found to be a more powerful phase transfer agent than TBA+ in a biphasic assay, enabling the direct fluorescence detection and quantification of GPS in water. A limit of detection of 1.45 µM and a linear range of 5–55 µM were obtained, which match well with WHO guidelines for the acceptable daily intake of GPS in water (5.32 µM).

All-silica optical fiber bonding.

In this work, we demonstrate a spot-welding method for fabrication of all-silica fiber components. A CO2 laser was used to locally sinter sub-micron silica powders, enabling rigid bonding of optical fiber to glass substrates. The bonding was achieved without inducing any fiber transmission losses. The components showed no sign of deterioration or structural change when heated up to 1100 °C. These single material assemblies are therefore well suited for use in harsh environments where high stability and robustness is required.

Thiourea- and Amino-Substituted Benzoxadiazole Dyes with Large Stokes Shifts as Red-Emitting Probe Monomers for Imprinted Polymer Layers Targeting Carboxylate-Containing Antibiotics.

Bifunctional fluorescent molecular oxoanion probes based on the benzoxadiazole (BD) chromophore are described which integrate a thiourea binding motif and a polymerizable 2‐aminoethyl methacrylate unit in the 4,7‐positions of the BD core. Concerted charge transfer in this electron donor‐acceptor‐donor architecture endows the dyes with strongly Stokes shifted (up to >250 nm) absorption and fluorescence. Binding of electron‐rich carboxylate guests at the thiourea receptor leads to further analyte‐induced red‐shifts of the emission, shifting the fluorescence maximum of the complexes to ≥700 nm. Association constants for acetate are ranging from 1–5×105 M−1 in acetonitrile. Integration of one of the fluorescent probes through its polymerizable moiety into molecularly imprinted polymers (MIPs) grafted from the surface of submicron silica cores yielded fluorescent MIP‐coated particle probes for the selective detection of antibiotics containing aliphatic carboxylate groups such as enoxacin (ENOX) at micromolar concentrations in highly polar solvents like acetonitrile.

Red-Emitting Polymerizable Guanidinium Dyes as Fluorescent Probes in Molecularly Imprinted Polymers for Glyphosate Detection

The development of methodologies to sense glyphosate has gained momentum due to its toxicological and ecotoxicological effects. In this work, a red-emitting and polymerizable guanidinium benzoxadiazole probe was developed for the fluorescence detection of glyphosate. The interaction of the fluorescent probe and the tetrabutylammonium salt of glyphosate was studied via UV/vis absorption and fluorescence spectroscopy in chloroform and acetonitrile. The selective recognition of glyphosate was achieved by preparing molecularly imprinted polymers, able to discriminate against other common herbicides such as 2,4-dichlorophenoxyacetic acid (2,4-D) and 3,6-dichloro-2-methoxybenzoic acid (dicamba), as thin layers on submicron silica particles. The limits of detection of 4.8 µM and 0.6 µM were obtained for the sensing of glyphosate in chloroform and acetonitrile, respectively. The reported system shows promise for future application in the sensing of glyphosate through further optimization of the dye and the implementation of a biphasic assay with water/organic solvent mixtures for sensing in aqueous environmental samples.

Experimental Measurement of Sharp THz Absorption Signatures from Nucleic Acid Solutions in Nanofluidic Channels

We report on the room-temperature experimental measurement of THz absorption signatures in aqueous, double-stranded nucleic acid solutions confined to the submicron silica channels on fused quartz substrates using THz frequency-domain (photomixing) spectroscopy. Three sharp (i.e., strong and narrow) signatures, ~10–20 GHz FWHM, are observed in the shortest base pair sample—small interfering, double-stranded (ds) RNA—in the range of 800 GHz to 1.1 THz. Three similar signatures are also observed in a 50-bp dsDNA ladder sample. For a 1-kbp dsDNA ladder sample, the three are still evident, but are broadened and weakened. For a 48.5-kbp sample (λ-DNA), no prominent signatures are observed, but rather a quasi-sinusoidal transmittance spectrum consistent with a substrate etalon effect. The division between sharp signatures and no signatures is consistent with the molecular length being shorter or longer than the persistence length.

Effects of desensitizing dentifrices on dentin tubule occlusion and resistance to erosive challenges

BackgroundMany studies have demonstrated efficacy of casein phosphopeptide (CPP) containing products for dentin tubule occlusion for treatment of dentin sensitivity, but their effectiveness under dynamic erosive challenges remains to be elucidated. The purpose of the present study was to investigate the effectiveness of a desensitizing dentifrice containing CPP in occluding dentin tubules and resisting erosive challenges in comparison to that containing polyvinyl methyl ether/maleic acid (PVM/MA) copolymers.Methods A total of 33 dentin discs were prepared from coronal sections of human third molars and divided into 3 groups: a toothpaste containing CPP; a toothpaste containing PVM/MA and submicron silica; and a regular toothpaste (Controls). A soft-bristle toothbrush was used to brush the dentin discs with the dentifrices for 45 strokes in 30 s at a force of approximately 200 g. The brushing cycle was repeated after immersion of the dentin discs in artificial saliva overnight. The dentin discs were then challenged in orange juice for 10 min in an incubator rocking at 120 rpm. Three fields were randomly selected on each dentin disk surface to assess dentin tubule occlusions after each brushing cycle and after orange juice challenge with a 3D laser scanning microscope. Specimen cross sections were examined with a scanning electron microscope equipped with energy dispersive spectroscopy (SEM/EDS).ResultsAfter the first and second cycles of brushing, dentin tubules were occluded on average by 56.3% and 85.7% in CPP group, 66.2% and 88.1% in PVM/MA group, and 0.0 and 13.0% in the controls, respectively. There were no statistically significant differences in dentin tubule occlusions between the CPP and PVM/MA groups after two cycles of brushing (p>0.05). After dynamic erosive challenges with orange juice, 20.3% of the dentin tubules in the CPP group, 79.1% in the PVM/MA group and none in the control remained occluded (P<0.05). SEM/EDS imaging showed that dentin tubules were blocked with plugs containing dentifrice substances in CPP and PVM/MA groups after treatments, but none in the controls.ConclusionsDesensitizing dentifrices containing CPP or PVM/MA could effectively occlude dentin tubules after two cycles of brushing. PVM/MA in combination with submicron silicon dioxide exhibited stronger resistance to dynamic erosive challenges by acidic beverages. Inorganic fillers that can enter dentin tubules and resist erosive challenges may be key for desensitizing dentifrices.

Shaping in the Third Direction; Synthesis of Patterned Colloidal Crystals by Polyester Fabric-Guided Self-Assembly.

A polyester fabric with rectangular openings was used as a sacrificial template for the guiding of a sub-micron sphere (polystyrene (PS) and silica) aqueous colloid self-assembly process during evaporation as a patterned colloidal crystal (PCC). This simple process is also a robust one, being less sensitive to external parameters (ambient pressure, temperature, humidity, vibrations). The most interesting feature of the concave-shape-pattern unit cell (350 μm × 400 μm × 3 μm) of this crystal is the presence of triangular prisms at its border, each prism having a one-dimensional sphere array at its top edge. The high-quality ordered single layer found inside of each unit cell presents the super-prism effect and left-handed behavior. Wider yet elongated deposits with ordered walls and disordered top surfaces were formed under the fabric knots. Rectangular patterning was obtained even for 20 μm PS spheres. Polyester fabrics with other opening geometries and sizes (~300–1000 μm) or with higher fiber elasticity also allowed the formation of similar PCCs, some having curved prismatic walls. A higher colloid concentration (10–20%) induces the formation of thicker walls with fiber-negative replica morphology. Additionally, thick-wall PCCs (~100 μm) with semi-cylindrical morphology were obtained using SiO2 sub-microspheres and a wavy fabric. The colloidal pattern was used as a lithographic mask for natural lithography and as a template for the synthesis of triangular-prism-shaped inverted opals.

Relationship between Occupational Exposure to Airborne Nanoparticles, Nanoparticle Lung Burden and Lung Diseases.

The biomonitoring of nanoparticles in patients’ broncho-alveolar lavages (BAL) could allow getting insights into the role of inhaled biopersistent nanoparticles in the etiology/development of some respiratory diseases. Our objective was to investigate the relationship between the biomonitoring of nanoparticles in BAL, interstitial lung diseases and occupational exposure to these particles released unintentionally. We analyzed data from a cohort of 100 patients suffering from lung diseases (NanoPI clinical trial, ClinicalTrials.gov Identifier: NCT02549248) and observed that most of the patients showed a high probability of exposure to airborne unintentionally released nanoparticles (>50%), suggesting a potential role of inhaled nanoparticles in lung physiopathology. Depending on the respiratory disease, the amount of patients likely exposed to unintentionally released nanoparticles was variable (e.g., from 88% for idiopathic pulmonary fibrosis to 54% for sarcoidosis). These findings are consistent with the previously performed mineralogical analyses of BAL samples that suggested (i) a role of titanium nanoparticles in idiopathic pulmonary fibrosis and (ii) a contribution of silica submicron particles to sarcoidosis. Further investigations are necessary to draw firm conclusions but these first results strengthen the array of presumptions on the contribution of some inhaled particles (from nano to submicron size) to some idiopathic lung diseases.

Submicron silica particles have cytotoxicities on hepatocellular carcinoma, non-small cell lung cancer and breast cancer by unified regulating the XLOC_001659/miR-98-5p/MAP3K2-mediated pathway.

The cytotoxicities of silica (SiO2s) particles against cancers are still controversial. In this study, the purchased submicron silica particles (SM-SiO2s) were identified by transmission electron microscopy and energy dispersive spectrometer, and it showed potent cytotoxicities on hepatocellular carcinoma (HCC), non-small cell lung cancer (NSCLC) and breast cancer (BC), which ranked the top in the incidence among the tumor types. Through the microarray assay on long noncoding RNAs (lncRNAs) from the SM-SiO2s-treated HCC, NSCLC and BC cells, followed by Venn analysis, we found that a series of lncRNAs were significantly regulated by SM-SiO2s, among of which XLOC_001659 was mostly decreased. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) assay confirmed that XLOC_001659 could be decreased in all the SM-SiO2s-treated HCC, NSCLC and BC cells, coupled to inhibited cell proliferation. Further, XLOC_001659 was recognized as a miR-98-5p sponge and therefore modulates the "pro-inflammatory tumor promoter" MAP3K2 expressions. The XLOC_001659/miR-98-5p/MAP3K2 axis uniformly mediated the regulation of SM-SiO2s on proliferation of HCC, NSCLC and BC cells. Further clinical experiments demonstrated that XLOC_001659 was negatively correlated with miR-98-5p level and positively correlated with MAP3K2 level, and XLOC_001659/miR-98-5p/MAP3K2 axis was significantly associated with progressions and prognosis in HCC, NSCLC and BC patients. These results provide a new clue for the anti-tumor mechanism of SM-SiO2s and a new way for drug development by using SM-SiO2s.

Ecotoxicological Assessment of DNA-Tagged Silica Particles for Environmental Tracing.

Environmental tracers are chemical species that move with a fluid and allow us to understand its origin and material transport properties. DNA-based materials have been proposed and used for tracing due to their potential for multitracing with high specificity and sensitivity. For large-scale applications of this new material it is of interest to understand its impact on the environment. We therefore assessed the ecotoxicity of sub-micron silica particles with and without encapsulated DNA in the context of surface and underground tracing of natural waterflows using standard ecotoxicity assays according to ISO standards. Acute toxicity tests were performed with Daphnia magna (48 h), showing no effect on mobility at tracer concentrations below 300 ppm. Chronic ecotoxicological potential was tested with Raphidocelis subcapitata (green algae) (72 h) and Ceriodaphnia species (7 d) with no effect observed at realistic exposure scenario concentrations for both silica particles with and without encapsulated DNA. These results suggest that large-scale environmental tracing with DNA-tagged silica particles in the given exposure scenarios has a low impact on aquatic species with low trophic levels such as select algae and planktonic crustaceans.

Micro-mesoporous submicron silica particles with pore size tunable in a wide range: synthesis, properties and prospects for LED manufacturing

An approach has been developed that allows the synthesis of submicron spherical silica particles with a controlled micro-mesoporous structure possessing a large specific surface area (up to 1300 m2 g−1). Particle synthesis is carried out by the hydrolysis of a mixture of various organosilanes mostly associated either with CTAB or with each other. A change in the concentration of CTAB in the reaction mixture apparently leads to a change in the formation mechanism of nuclei for the silica particle growth, which allows for varying the diameter of the synthesized particles in the range from 40–450 nm. The effect of the composition of the silica precursor ([3-(methacryloyloxy)propyl]trimethoxysilane, (3-aminopropyl)triethoxysilane and tetraethoxysilane) on the formation process and porosity of the resulting particles is studied. It was shown that by simply varying the ratio of organosilanes in the composition of the precursor, one can control the pore diameter of the particles in a wide range from 0.6–15 nm. The large-pore (up to 15 nm) silica particles are used as a matrix for the spatial distribution of luminescent carbon dots. The incorporation of carbon dots into SiO2 particles prevents their aggregation leading to emission quenching after drying, thus allowing us to obtain highly luminescent composite particles. LEDs based on the obtained composite material show bright visible luminescence with spectral characteristics similar to that of a commercial cold white LED.

Facile and rapid ultrasound-mediated synthesis of spherical mesoporous silica submicron particles with high surface area and worm-like mesoporosity

Here, a facile and rapid ultrasound-mediated synthesis at ambient conditions is proposed for production of novel spherical mesoporous silica submicron particles (MSP) with high specific surface area (SSA) and high worm-like mesoporosity. A one-pot synthesis was designed to involve soft-templating with cationic surfactant cetyltrimethylammonium bromide (CTAB), application of high-power ultrasound (Us) for hydrolysis/condensation of tetraethyl orthosilicate (TEOS) in methanol/NH4OH solution and vigorous magnetic stirring. Spherical MSP with worm-like mesoporous structure were produced with average particle diameter ~545 nm, SSA ca. 1544 m2/g, total pore volume as high as 0.75 cm3/g and NLDFT pore diameter of 2.94 nm. The developed MSP hold great promise for applications e.g. H2 storage, CO2 capture, removal of Hg from gas as well as drug delivery.

Highly Dispersed RuOOH Nanoparticles on Silica Spheres: An Efficient Photothermal Catalyst for Selective Aerobic Oxidation of Benzyl Alcohol

HighlightsUltrasmall RuOOH nanoparticles of 2–3 nm are loaded on submicron silica spheres and capable of activating molecular oxygen.Photothermal conversion efficiency of the supported RuOOH nanoparticles is nearly unity.Photothermal effect promotes selective oxidation of benzyl alcohol under the illumination of visible light.