SiO2 NP Research Articles

Adsorption behavior of some metal ions on nanoparticles used in pharmaceutical matrices: Application to laboratory made drug formulation

The adsorption behavior of some metal ions (Pb, Mn, Mg, Zn and Ca) was studied on silicon dioxide nanoparticles, SiO2 NP, alone and its mixture with microcrystalline cellulose, MCC, powder (1:1) as drug carriers in pharmaceutical preparations. The effect of different conditions as temperature and pH on adsorption was investigated. It was found that upon increasing the temperature, the ability of the adsorbent material increases. The pH of the metal solution has the same effect as temperature till pH 8. However, above pH 8 the adsorbent material began to lose its adsorption efficiency. Although, the use of SiO2 NP mixture with MCC powder can improve the excipient functionality, it is important to take into consideration their metal adsorption behavior. The study was applied on laboratory made drug formulation contains different drug carriers. The study points at the importance of adjusting the permissible level of metals in different active and inactive ingredients used in pharmaceutical preparations containing nanoparticles as drug carriers. The type of nanoparticles used and the pH of these preparations are important factors affecting the metal adsorption behavior. At the maximum temperature of adsorption, the calculated metal adsorption capacity of a mixture of MCC and SiO2 NP (1:1) compared to SiO2 NP alone was found to be 0.2043 and 0.1169 for Pb, 0.1948 and 0.1041 for Zn, 0.2114 and 0.1207 for Mg, 0.2220 and 0.1222 for Ca and 0.2068 and 0.1054 for Mn, respectively. Flame atomic spectrometry was used for determining metal remained concentration after adsorption.

Interfacial engineering of hole transport layers with metal and dielectric nanoparticles for efficient perovskite solar cells.

In this work, we have demonstrated the incorporation of metal (Ag NPs) and dielectric nanoparticles (SiO2 NPs) into the hole transporting layers of inverted PSCs using facile deposition methods. Interfacial engineering in PSCs is accomplished by incorporating 50 nm Ag NPs or SiO2 NPs within the PEDOT:PSS interlayer. Dielectric SiO2 NPs were used for comparison purposes as a control sample to isolate morphological impacts without plasmonic effects. The photovoltaic performance of the devices significantly improved due to increased charge selectivity and enhanced charge collection properties across the interface (HTL). The recombination resistance of the SiO2 NP incorporated HTL based PSCs was 193% higher than that of the conventional devices. In-depth analysis using impedance measurements revealed that devices containing Ag or SiO2 NPs have low electrode polarization and consequently lower charge accumulation at the interface. Lower electrode polarization in the modified devices was also found to improve the charge carrier selectivity, which eventually led to enhanced fill factor and lower parasitic resistances. Interfacial engineering via NPs yielded improvements in the electrical characteristics of non-optical origin, which not only enhanced device performance, but also reduced the hysteresis effects to much lower than in the conventional inverted PSCs based on a pristine PEDOT:PSS interlayer.

Transcriptional activation of follistatin by Nrf2 protects pulmonary epithelial cells against silica nanoparticle-induced oxidative stress.

Silica nanoparticles (SiO2 NPs) cause oxidative stress in respiratory system. Meanwhile, human cells launch adaptive responses to overcome SiO2 NP toxicity. However, besides a few examples, the regulation of SiO2 NP-responsive proteins and their functions in SiO2 NP response remain largely unknown. In this study, we demonstrated that SiO2 NP induced the expression of follistatin (FST), a stress responsive gene, in mouse lung tissue as well as in human lung epithelial cells (A549). The levels of Ac-H3(K9/18) and H3K4me2, two active gene markers, at FST promoter region were significantly increased during SiO2 NP treatment. The induction of FST transcription was mediated by the nuclear factor erythroid 2-related factor 2 (Nrf2), as evidenced by the decreased FST expression in Nrf2-deficient cells and the direct binding of Nrf2 to FST promoter region. Down-regulation of FST promoted SiO2 NP-induced apoptosis both in cultured cells and in mouse lung tissue. Furthermore, knockdown of FST increased while overexpression of FST decreased the expression level of NADPH oxidase 1 (NOX1) and NOX5 as well as the production of cellular reactive oxygen species (ROS). Taken together, these findings demonstrated a protective role of FST in SiO2 NP-induced oxidative stress and shed light on the interaction between SiO2 NPs and biological systems.

Interferences of Silica Nanoparticles in Green Fluorescent Protein Folding Processes.

We investigated the relationship between unfolded proteins, silica nanoparticles and chaperonin to determine whether unfolded proteins could stick to silica surfaces and how this process could impair heat shock protein activity. The HSP60 catalyzed green fluorescent protein (GFP) folding was used as a model system. The adsorption isotherms and adsorption kinetics of denatured GFP were measured, showing that denaturation increases GFP affinity for silica surfaces. This affinity is maintained even if the surfaces are covered by a protein corona and allows silica NPs to interfere directly with GFP folding by trapping it in its unstructured state. We determined also the adsorption isotherms of HSP60 and its chaperonin activity once adsorbed, showing that SiO2 NP can interfere also indirectly with protein folding through chaperonin trapping and inhibition. This inhibition is specifically efficient when NPs are covered first with a layer of unfolded proteins. These results highlight for the first time the antichaperonin activity of silica NPs and ask new questions about the toxicity of such misfolded proteins/nanoparticles assembly toward cells.

Engineered silica nanoparticles as additives in lubricant oils

Silica nanoparticles (SiO2 NPs) synthesized by the sol–gel approach were engineered for size and surface properties by grafting hydrophobic chains to prevent their aggregation and facilitate their contact with the phase boundary, thus improving their dispersibility in lubricant base oils. The surface modification was performed by covalent binding of long chain alkyl functionalities using lauric acid and decanoyl chloride to the SiO2 NP surface. The hybrid SiO2 NPs were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, simultaneous differential thermal analysis, nuclear magnetic resonance and dynamic light scattering, while their dispersion in two base oils was studied by static multiple light scattering at low (0.01% w/v) and high (0.50%w/v) concentrations. The nature of the functional layer and the functionalization degree seemed to be directly involved in the stability of the suspensions. The potential use of the functional SiO2 NPs as lubricant additives in base oils, specially designed for being used in hydraulic circuits, has been outlined by analyzing the tribological properties of the dispersions. The dendritic structure of the external layer played a key role in the tribological characteristics of the material by reducing the friction coefficient and wear. These nanoparticles reduce drastically the waste of energy in friction processes and are more environmentally friendly than other additives.

Selective removal of toxic anionic dyes using a novel nanocomposite derived from cationically modified guar gum and silica nanoparticles

A novel nanocomposite derived from cationically modified guar gum and in-situ incorporated SiO2 NP (cat-GG/SiO2) has been developed. The cat-GG has been synthesised by grafting poly(2-(diethylamino)ethyl methacrylate) on GG backbone. Various analyses endorse the suitability of cat-GG as well-organized template for the development of homogeneous SiO2 NPs. Dye adsorption studies predict that cat-GG/SiO2 efficiently and selectively adsorb anionic dyes (reactive blue—RB and Congo red—CR) from mixture of dye solutions. This is because of high surface area, multifunctional chelating H-bonding interactions and electrostatic interactions of cationic adsorbent with anionic dyes. Dyes adsorbed on the composite surface are desorbed reversibly using pH 10 stripping solution. Besides, cat-GG/SiO2 has been recycled efficiently with no prominent loss of dye uptake capacity, even after 4 adsorption–desorption cycles.

Unique Surface Modification of Silica Nanoparticles with Polyethylenimine (PEI) for siRNA Delivery Using Cerium Cation Coordination Chemistry.

The discovery of RNA interference (RNAi) as a naturally occurring mechanism for gene knockdown has attracted considerable attention toward the use of small interfering RNAs (siRNAs) for therapeutic purposes. The main obstacles of harnessing siRNAs as drugs are their inefficient delivery to cells and off-target effect making clinical applications very challenging. The positively charged, branched 25 kDa polyethylenimine (b-PEI) polymer is widely regarded as one of the most efficient nonviral commercially available transfection agents. However, it has also been shown that 25 kDa b-PEI is highly cytotoxic and can readily lead to cell death. In this specific context, this study presents the preparation and characterization of innovative 25 kDa b-PEI-decorated polycationic silica nanoparticles (SiO2 NPs) for cellular siRNA delivery and subsequent gene silencing. A new method of b-PEI attachment onto the SiO2 NP surface has been developed that makes use of cerium(III) cations (Ce(3+)), a lanthanide group element, as an effective noncovalent inorganic linker between both polyNH2-SiO2 nanoparticle (SPA NPs) surface and polycationic 25 kDa b-PEI polymer. Two resulting novel SPA-Ce-PEI NPs consist of similar amounts of b-PEI, while possessing different amounts of Ce(3+). Various analytical techniques (TEM, DLS, ζ potential, ICP-AES, and TGA) have been used to deeply characterize NPs physicochemical qualities. The observed results of Ce(3+)-dependent gene silencing and cytotoxic activities led us to conclusions about the role of Ce(3+)-N bonding during the chemical attachment of the 25 kDa b-PEI shell onto the NP surface.

Fate of fluorescent core-shell silica nanoparticles during simulated secondary wastewater treatment

Increasing use of silica nanoparticles (SiO2 NPs) in consumer products and industrial processes leads to SiO2 NP discharge into wastewater. Thus, there is a need to understand the fate of SiO2 NPs during wastewater treatment. However, the detection of SiO2 NPs in environmental systems is hindered by the elevated background levels of natural silicon. In this work, laboratory-synthesized fluorescent core-shell SiO2 NPs were used to study the fate of these NPs during secondary wastewater treatment. Fluorescent measurements provided an easy and fast method for SiO2 NP tracking. A laboratory-scale activated sludge system consisting of an aeration tank and a settler was fed with synthetic wastewater containing ca. 7.5 mg L−1 of fluorescent SiO2 NPs for 30 days. SiO2 NPs were effectively removed from the wastewater (>96%) during the first 6 days, however the concentration of SiO2 NPs in the effluent gradually increased afterwards and the NP discharge was as high as 65% of the input after 30 days of NP dosing. The poor removal of the SiO2 NPs was related to the high colloidal stability of the NPs in the wastewater and their limited propensity to biosorption. Although some degree of NP adsorption on the biomass was observed using fluorescence microscopy, the affinity of SiO2 NPs for the activated sludge was not enough for a sustained and effective removal of the SiO2 NPs from the wastewater.

A SiO2 NP-DNA/silver nanocluster sandwich structure-enhanced fluorescence polarization biosensor for amplified detection of hepatitis B virus DNA.

A novel homogeneous biosensor based on the fluorescence polarization enhancement effect of the SiO2 NP-DNA/Ag nanocluster sandwich structure has been developed for sensitive and selective detection of hepatitis B virus DNA.

Size and Cell Type Dependent Uptake of Silica Nanoparticles

As silica nanoparticles (SiO2 NP) gain increasing interest for medical applications it is important to understand their potential adverse effects for humans. Here we prepared well-defined core-shell fluorescently labelled SiO2 NP of 15, 60 and 200 nm diameter and analyzed their cytotoxicity in THP-1 derived macrophages, A549 epithelial cells, HaCaT keratinocytes and NRK-52E kidney cells. We observed a size-dependent cytotoxicity in all cell types in serumfree conditions. HaCaT cells were least and macrophages or lung derived A549 cells were highly sensitive towards SiO2 NP treatment. Differences in cytotoxicity could be correlated with different uptake rates. By using flow cytometry and confocal microscopy we quantified the uptake. Furthermore we used specific inhibitors for clathrin- and caveolinmediated endocytosis to elucidate the uptake mechanisms, which were found to be dependent on the NP size and the cell type. Clathrin-mediated endocytosis was involved in the uptake of SiO2 NP of all sizes and was the major pathway for 60 nm or 200 nm SiO2 NP. Caveolin-mediated endocytosis contributed to the uptake of 60 and 200 nm SiO2 NP in THP-1 macrophages but only to uptake of 200 nm SiO2 NP in A549. However, in the presence of serum all SiO2 NP were non-toxic. The presence of serum furthermore could alter the uptake mechanism. In summary, this study demonstrates size- and cell type dependent differences in SiO2 NP uptake and toxicity.

Silica Nanoparticles and Polyethyleneimine (PEI)-Mediated Functionalization: A New Method of PEI Covalent Attachment for siRNA Delivery Applications

Small-interfering RNA (siRNA) is a synthetic double-stranded RNA that consists of approximately 21 nucleotides (nts). It induces degradation of target mRNAs in a sequence-specific manner by the RNA interference (RNAi) mechanism. Thus, siRNAs offer a potential strategy for silencing mutated or defective genes that cause a variety of human diseases. The main obstacles of harnessing siRNAs as drugs are their inefficient delivery to cells and off-target effect making clinical applications very challenging. To address these issues, researchers have studied a variety of nanocarrier systems for siRNA delivery. This study presents the design, fabrication, and full characterization of innovative polyethyleneimine (PEI)-decorated polycationic 34.2 ± 4.2 nm silica (SiO2) NPs for siRNA-mediated gene silencing. More specifically, a new means of introduction (covalent mode of attachment) of the polycationic 25 kDa PEI polymer onto the SiO2 NP surface has been developed that makes use of an effective electrophilic double Michäel acceptor, divinyl sulfone (DVS). The resulting novel SiO2-PEI nanoparticles (SPEI NPs) have been fully characterized using a wide range of analytical, spectroscopic, and microscopic methods (TEM, DLS, ζ potential, elemental analysis (EA), XPS, TGA, and FTIR). Disclosing quite low cytotoxicity due to this unique mode of PEI covalent grafting, SPEI NPs/siRNA polyplexes have been successfully tested for the induction of gene silencing using dual-reporter luciferase transfected human osteosarcoma U2OS cells. The corresponding gene silencing data showed a clear correlation between PEI/siRNA ratios, siRNA concentration(s), and the level of gene silencing. Moreover, these SPEI NPs have been demonstrated to be thermodynamically stable with an ability to efficiently bind siRNAs and induce silencing for at least a one-year-long storage.

Monitoring migration and transformation of nanomaterials in polymeric composites during accelerated aging

The incorporation of small amounts of nanoadditives in polymeric compounds can introduce new mechanical, physical, electrical, magnetic, thermal and/or optical properties. The properties of these advanced materials have enabled new applications in several industrial sectors (electronics, automotive, textile...). In particular, for the nanomaterials (NM) described in this work, multi-walled carbon nanotubes (MWCNT) and silicon dioxide nanoparticles (SiO2 NP), the following properties have been described: MWCNT act as nucleating agents in thermoplastics, and change viscosity, affecting dispersion, orientation, and therefore mechanical, thermal, and electrical properties; and SiO2 NP act as flame retardant and display improved electrical and mechanical properties.The work described here is focused on the evaluation of the migration and transformation of NM included in polymer nanocomposites (NC) during accelerated climatic ageing. To this aim, we generated polyamide 6 (PA6) NC with different degree of compatibility between the NM and the polymeric matrix. These NC were submitted to accelerated aging conditions to simulate outdoor conditions (simulation of the use phase of the polymeric NC). The NC contain as nanofillers MWCNT and SiO2 NP with different surface properties to influence the compatibility with the polymeric matrix. The generated NC were evaluated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) with Energy-dispersive X-ray spectroscopy (EDX), thermogravimetry (TGA) and differential scanning calorimetry (DSC) before and after the aging process, to monitor the compatibility of the NM with the matrix: dispersion within the matrix, migration during aging, and modification of the polymer properties.The dispersion of SiO2 NP in the NC depended on their compatibility with the matrix. However, independently of their compatibility with the matrix, SiO2 NP were aggregated at the end of the accelerated aging process. In addition, degradation of the matrix and migration of nanoparticles to the surface was observed as well in the different types of SiO2 NP aged NC. Oppositely, compatibilized MWCNT (MWCNTMB) decreased the degradation of the polymer. Nevertheless, the nanomaterial migrated likewise to the surface during the ageing process.In order to evaluate the possible changes in the structure of nanomaterials due to the aging process, NM were extracted from the polymer by calcination. The nanomaterials extracted were analyzed by TGA, Fourier transform infrared spectroscopy (FT-IR), BET and TEM and its properties compared with calcinated raw NM. SiO2 hydrophilic nanoparticles were not affected by the aging process. However, both types of MWCNT were affected by the aging of the NC.

Electrostatically driven adsorption of silica nanoparticles on functionalized surfaces

Adsorption of nanoparticles on solid supports is a scientifically interesting and technologically important phenomenon that has been attracting ever-increasing attention. Formation of particle-based films onto surfaces from stable suspensions is at the center of the development of new devices that utilize the plethora of newly synthesized nanoparticles with exciting properties. In this study we exploit the attractive electrostatic interactions between silica (SiO2) nanoparticles and functionalized substrates that display an amine termination in order to devise a simple method for the fabrication of SiO2 nanoparticle films. Electrostatically controlled adsorption allows for uniform coverage of nanoparticles over large areas. The Stöber method (a sol–gel approach) was employed to prepare uniformly sized SiO2 nanoparticles with a diameter of 50–80nm. Native oxide-covered silicon wafer substrates were amino-functionalized utilizing the self-assembled monolayer of 3-aminopropyltrimethoxysilane (APS). The adsorption of SiO2 nanoparticle film onto the silicon wafer substrate was controlled by modulation of the electrostatic interaction between nanoparticles and the substrate. Modification of surface charge of either the SiO2 NP or the substrate is a crucial step in the process. Thus the effect of APS adsorption time on the surface energy of the substrate was investigated. Also, process parameters such as NP concentration and solvent composition were varied in order to investigate the extent of NP adsorption. Moreover, NaCl was introduced to the SiO2 suspension as a charge-screening agent to reduce the inter-particle repulsion in the suspension as well as interaction of the particles with the surface. This resulted in denser/thicker films.

A role of silica nanoparticles in layer-by-layer self-assembled carbon nanotube and In2O3 nanoparticle thin-film pH sensors: Tunable sensitivity and linearity

A role of the dielectric silica nanoparticle (SiO2 NP) in nanomaterial chemoresistors and ion-sensitive field-effect transistors (ISFET) is demonstrated in this study. Single-walled carbon nanotubes (SWCNT) and indium oxide nanoparticles (In2O3 NP) are layer-by-layer self-assembled alternately with oppositely charged polyelectrolytes, respectively. Nanomaterial multilayer thin-film is patterned using photolithography and electrochemically characterized in various pH buffers. The pH sensors are implemented as resistor and transistor in absence and presence of SiO2 NP layer. We observed tunable sensitivity and linearity of output current flowing through the conducting channel in SWCNT chemoresistor and ISFET. The role of SiO2 NP is proven to modulate and linearize the sensitivity to pH. The linearization is attributed to a positive shift in pH gating voltage in p-type semiconducting SWCNTs. On the other hand, a tunable sensitivity is observed whereas the linearization is not demonstrated in In2O3 NP ISFETs. The increased sensitivity with SiO2 NP in acidic region is caused by a positive shift in gate voltage due to the protonation of the surface hydroxyl groups. This facile modulation and linearization of the electrochemical sensitivity in semiconducting nanomaterial thin-film device by means of the additional SiO2 NP layer is useful for developing various functional nanomaterial-based biosensors.

Temperature-response polymer coating for in-tube solid-phase microextraction coupled to high-performance liquid chromatography

The silica nanoparticle (SiO2 NP)-deposited capillary fabricated by liquid phase deposition (LPD) was bonded by 3-(triethoxysilyl) propyl methacrylate and then modified with poly(N-isopropylacrylamide) (PNIPAAm) by polymerization. The resulting PNIPAAm modified SiO2 NP-deposited capillary was applied to in-tube solid-phase microextraction coupled to high-performance liquid chromatography (in-tube SPME–HPLC). To investigate the extraction performance of the prepared capillary, diethylstilbestrol (DES) with moderate polarity was selected as the model analyte. Results demonstrate that PNIPAAm modified SiO2 NP-deposited capillary exhibited obvious temperature responsive character. Finally, the PNIPAAm modified SiO2 NP-deposited capillary was applied to the analysis of three synthetical estrogens from milk samples. The detection limit of the method was found to be in the range 1.2–2.2ng/g, and recovery was 71.7–98.9% with relative standard deviations in the range of 2.8–12.6%.

Preparation of Nanoporous Polyelectrolyte Multilayer Films via Nanoparticle Templating

Polyelectrolyte−nanoparticle hybrid multilayer films were used as templates for the preparation of nanoporous polymer thin films. The hybrid multilayers were constructed by consecutively depositing an anionic blend of silica nanoparticles (SiO2 NPs) and poly(acrylic acid) (PAA) and a cationic polyelectrolyte, poly(allyamine hydrochloride) (PAH). Layer-by-layer growth of the multilayers with different SiO2 NP sizes (25, 45, and 85 nm in diameter) and at different pH was followed by quartz crystal microgravimetry (QCM). Film buildup, as assessed by QCM mass changes, was 3 times larger when assembled with PAH at pH 9 than with PAH at pH 5. After chemically cross-linking the PAA/PAH within the films, the SiO2 NPs were removed by dissolution with hydrofluoric acid. Atomic force microscopy and transmission electron microscopy were used to characterize the porous films formed and revealed that the pore size could be controlled by using SiO2 NPs of different size. The adsorption of bovine serum albumin (BSA) on the porous thin films showed that the amount of BSA adsorbed increased with increasing bilayer number, suggesting the protein infiltrated the films. This provides opportunities to tune the protein content in the films, which is of interest for applications in biocatalysis and biosensing.