Chitosan–SiO2–multiwall carbon nanotubes nanocomposite: A novel matrix for the immobilization of creatine amidinohydrolase

A matrix made up of chitosan–SiO₂–multiwall carbon nanotubes (CHIT–SiO₂–MWCNTs) nanocomposite was fabricated to investigate the immobilization of creatine amidinohydrolase (CAH). CAH enzyme was covalently immobilized with the CHIT–SiO₂–MWCNTs matrix using glutaraldehyde as a linker. The resulting CAH/CHIT–SiO₂–MWCNTs biomatrix was characterized with Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and cyclic voltammetry (CV) taking CHIT–SiO₂–MWNTs as a reference. The influence of various parameters on CAH enzyme activity within the matrix was investigated including pH, temperature, and time. The Michaelis–Menten constant and apparent activities for the CAH enzyme were calculated to be 0.58 mM and 83.16 mg/cm², respectively; indicating CHIT–SiO₂–MWCNTs nanocomposite matrix has a high affinity to immobilize CAH enzyme.     

Heat insulation performance,mechanics and hydrophobic modification of cellulose–SiO2 composite aerogels

Cellulose–SiO₂ composite hydrogel was prepared by combining the NaOH/thiourea/H₂O solvent system and the immersion method with controlling the hydrolysis–fasculation rate of tetraethyl orthosilicate (TEOS). The hydrophobic composite aerogels were obtained through the freeze-drying technology and the cold plasma modification technology. Composite SiO₂ could obviously reduce the thermal conductivity of cellulose aerogel. The thermal conductivity could be as low as 0.026 W/(mK). The thermal insulation mechanism of the aerogel material was discussed. Composite SiO₂ reduced hydrophilicity of cellulose aerogel, but environmental humidity had a significant influence on heat insulation performance. After hydrophobic modification using CCl₄ as plasma was conducted, the surface of composite aerogel was changed from hydrophilic to hydrophobic and water contact angle was as high as 132°. The modified composite aerogel still kept good heat insulation performance. This work provided a foundation for the possibility of applying cellulose–SiO₂ composite aerogel in the insulating material field.     

A highly sensitive fluorescence sensor based on lucigenin/chitosan/SiO2 composite nanoparticles for microRNA detection using magnetic separation

In this paper, a convenient reverse‐phase microemulsion method for the synthesis of SiO₂ nanoparticles (NPs) by simply introducing the chitosan and fluorescent dye of lucigenin during the formation reaction of SiO₂ NPs was proposed. Addition of chitosan can make the SiO₂ NPs porous, and increases lucigenin molecule incorporation into chitosan/SiO₂ NPs nanopores based on electrostatic interaction and supermolecular forces. Therefore, fluorescence quantum yield of the lucigenin/chitosan/SiO₂ composite nanoparticles was increased by introduction of chitosan and compared with lucigenin/SiO₂ NPs without chitosan. Because the number of negative charges carried when using single‐stranded DNA (ssDNA) was different from that of double‐stranded DNA (dsDNA), the numbers of lucigenin/chitosan/SiO₂ composite nanoparticles with positive charge adsorbed using ssDNA or dsDNA were different. Consequently, fluorescence intensity caused using ssDNA or dsDNA/miRNA was clearly discriminative. With increase in target DNA/miRNA concentration, the difference in fluorescence intensity also increased, resulting in a good linear relationship between fluorescence intensity sensitizing value and target miRNA concentrations. Therefore, a new fluorescence analysis method for direct detection of let‐7a in human gastric cancer cell samples without enzyme, label free and no immobilization was established using lucigenin/chitosan/SiO₂ composite nanoparticles as a DNA hybrid indicator. The proposed method had high sensitivity and selectivity, low cost and the detection limit was 10 fM (S/N = 3).     

Comparative study of three magnetic nano-particles (FeSO4, FeSO4/SiO2, FeSO4/SiO2/TiO2) in plasmid DNA extraction

Recent updates on Magnetic Nano-Particles (MNPs) based separation of nucleic acids have received more attention due to their easy manipulation, simplicity, ease of automation and cost-effectiveness. It has been indicated that DNA molecules absorb on solid surfaces via hydrogen-bonding, and hydrophobic and electrostatic interactions. These properties highly depend on the surface condition of the solid support. Therefore, surface modification of MNPs may enhance their functionality and specification. In the present study, we functionalized Fe₃O₄ nano-particle surface utilizing SiO₂ and TiO₂ layer as Fe₃O₄/SiO₂ and Fe₃O₄/SiO₂/TiO₂ and then compare their functionality in the adsorption of plasmid DNA molecules with the naked Fe₃O₄ nano-particles. The result obtained showed that the purity and amount of DNA extracted by Fe₃O₄ coated by SiO₂ or SiO₂/TiO₂ were higher than the naked Fe₃O₄ nano-particles. Furthermore, we obtained pH 8 and 1.5 M NaCl as an optimal condition for desorption of DNA from MNPs. The result further showed that, 0.2 mg nano-particle and 10 min at 55 °C are the optimal conditions for DNA desorption from nano-particles. In conclusion, we recommended Fe₃O₄/SiO₂/TiO₂ as a new MNP for separation of DNA molecules from biological sources.     

The role of reactive oxygen species in silicon dioxide nanoparticle-induced cytotoxicity and DNA damage in HaCaT cells

The increasing applications of silicon dioxide (SiO₂) nanomaterials have been widely concerned over their biological effects and potential hazard to human health. In this study, we explored the effects of SiO₂ nanoparticles (15, 30, and 100 nm) and their micro-sized counterpart on cultured human epidermal Keratinocyte (HaCaT) cells. Cell viability, cell morphology, reactive oxygen species (ROS), DNA damage (8-OHdG, γH2AX and comet assay) and apoptosis were assessed under control and SiO₂ nanoparticles exposed conditions. As observed in the Cell Counting Kit-8 (CCK-8) assay, exposure to 15, 30 or 100 nm SiO₂ nanoparticles at dosage levels between 0 and 100 μg/ml decreased cell viability in a concentration- and size dependent manner and the IC50 of 24 hour exposure was 19.4 ± 1.3, 27.7 ± 1.5 and 35.9 ± 1.6 μg/ml for 15, 30 and 100 nm SiO₂ nanoparticles, respectively. Morphological examination revealed cell shrinkage and cell wall missing after SiO₂ nanoparticle exposure. Increase in intracellular ROS level and DNA damage as well as apoptosis were also observed in SiO₂ nanoparticle-exposed HaCaT cells. Exposure to SiO₂ nanoparticles results in a concentration- and size-dependent cytotoxicity and DNA damage in cultural HaCaT cells which is closely correlated to increased oxidative stress.     

Study of the controlled assembly of DNA gated PEI/Chitosan/SiO2 fluorescent sensor

In this paper, polyethylenimine (PEI) and Chitosan were simultaneously one‐step doped into silicon dioxide (SiO₂) nanoparticles to synthesize PEI/Chitosan/SiO₂ composite nanoparticles. The polymer PEI contained a large amount of amino groups, which can realize the amino functionalized SiO₂ nanoparticles. And, the good pore forming effect of Chitosan was introduced into SiO₂ nanoparticles, and the resulting composite nanoparticles also had a porous structure. In pH 7.4 phosphate buffer solution (PBS), the amino groups of PEI had positive charges, and therefore the fluorescein sodium dye molecule can be loaded into the channels of PEI/Chitosan/SiO₂ composite nanoparticles by electrostatic adsorption. Furthermore, utilizing the diversity of DNA molecular conformation, we designed a high sensitive controllable assembly of DNA gated fluorescent sensor based on PEI/Chitosan/SiO₂ composite nanoparticles as loading materials. The factors affecting the sensing performance of the sensor were investigated, and the sensing mechanism was also further studied.     

Biocatalytic characterization of Aspergillus oryzae β-galactosidase immobilized on functionalized multi-walled carbon nanotubes

The objectives of this work were to immobilize commercial Aspergillus oryzae β-galactosidase on functionalized multi-walled carbon nanotubes (MWCNTs) using different treatments and to characterize the products. Treatments were performed with glutaraldehyde, ethylenediamine and a mixture of concentrated H₂SO₄:HNO₃. The MWCNTs and their derivatives were characterized by thermogravimetric analysis. The immobilized enzymes were evaluated using inactivation kinetics, operating conditions, that is pH and temperature, kinetic parameters and lactose hydrolysis reusability. Immobilization yield and efficiency were significantly higher for β-galactosidase immobilized on MWCNTs functionalized by the acid mixture (Ac-Gal-MWCNTs). These values were 97% and 82%, respectively, after 3?h of immobilization. The activity of the Ac-Gal-MWCNTs was maintained at ～51% of their initial activity after being stored for 90 days at 4?°C. The Ac-Gal-MWCNTs retained more than 90% of their initial activity up to the fourth recycle. As the acid functionalization was the most efficient method tested for immobilizing A. oryzae β-galactosidase on MWCNTs, this method shows promise for industrial applications.     

Tunable In-Plane Optical Anisotropy of Ag Nanoparticles Deposited by DC Sputtering onto SiO<Subscript>2</Subscript> Nanocolumnar Films

This work reports an easy-to-handle method for growing two-dimensional assemblies of Ag nanostructures presenting a tunable in-plane optical anisotropy. Ag is deposited by DC sputtering in an Ar plasma at room temperature onto bundled nanocolumnar SiO₂ thin films grown by glancing angle physical vapor deposition. In contrast with previously reported processes involving the grazing angle deposition of the metal, DC sputtering is performed at normal incidence. By varying the deposition angle of SiO₂ and the Ar pressure, it was possible to tune the deposited amount of Ag and thus the topology of the Ag deposit from isolated spherical Ag nanoparticles with isotropic optical properties to strongly dichroic Ag nanostripes oriented along the bundling direction of the SiO₂ nanocolumns. Based on simple calculations taking into account the shadowing effects during metal deposition, it is proposed that the width and shape of the tip of the bundled SiO₂ nanocolumns influence significantly the metal local atom flux arriving to them and thus the final structure of the deposit.     

The effect of silica-treated macrophages on the synthesis of collagen and other proteins in vitro

Treatment with SiO₂ releases from peritoneal macrophages a soluble factor which stimulates the synthesis of collagen and other proteins in incubated slices of experimental granulation tissue. This factor can also be obtained by SiO₂-treatment from certain subcellular particles of intact macrophages. A similar agent is released from the macrophages by incubation with rheumatoid synovialtissue extract. Macrophages induced by paraffin or thioglycollate medium cannot be stimulated further by SiO₂. The SiO₂-treated macrophages have no effect on detached matrix-free cells from embryonic-chick tendon or granulation tissue. Another factor from macrophages, present in the 100000 g-supernatant of the homogenate, inhibits the synthesis of collagen in granuloma slices. The synthesis of DNA and RNA in slices is suppressed by the extract from intact macrophages but not affected by preparations obtained with SiO₂. The possible relevance of these findings to lysosomal actions, to the regulation of granuloma formation and to inflammation are discussed.     

Silicification of developing internodes in the perennial scouring rush (Equisetum hyemale var. affine)

An electron microprobe (EMP) analysis of silica (SiO₂) deposition in the epidermis of developing internodes of the perennial scouring rush (Equisetum hyemale var. affine) indicates that SiO₂ is first detected in the stomatal apparatus beginning with internode 3, then the epidermal papillae (internode 8), and finally in radial cell walls of the long epidermal cells (internode 10). This process is initiated in the intercalary growth regions at the bases of the elongating internodes. The deposition of SiO₂ in long epidermal cell walls occurs after internodal extension has ceased and should therefore be considered as one of the final stages in internodal differentiation that involves strengthening the cellulosic framework of the cell wall. EMP measurements indicate that SiO₂ in stomata is equivalent to 30% of a pure SiO₂ standard and that SiO₂ in the radial walls of long epidermal cells averages twice that measured on the tangential walls of these same cells. This study supports the view that silicification plays a major role in strengthening the developing perennial scouring rush internodal system and that regulation of this process in this and other species of Equisetum, whose SiO₂ deposition patterns are markedly different, deserves further study.     

Cleavable ester-linked magnetic nanoparticles for labeling of solvent-exposed primary amine groups of peptides/proteins

To study the solvent-exposed lysine residues of peptides/proteins, we previously reported disulfide-linked N-hydroxysuccinimide ester-modified silica-coated iron oxide magnetic nanoparticles (NHS–SS–SiO₂@Fe₃O₄ MNPs). The presence of a disulfide bond in the linker limits the use of disulfide reducing agent during protein digestion and allows unwanted disulfide formation between the MNPs and protein. In the current work, the disulfide bond was replaced with a cleavable ester group to synthesize NHS ester-modified SiO₂@Fe₃O₄ MNPs. Use of the cleavable ester group provides an improved method for protein labeling and allows the use of disulfide reducing agents during protein digestion.     

An on-chip thin film photodetector for the quantification of DNA probes and targets in microarrays

A flat microdevice which incorporates a thin-film amorphous silicon (a-Si:H) photodetector with an upper layer of functionalized SiO₂ is used to quantify the density of both immobilized and hybridized DNA oligonucleotides labeled with a fluorophore. The device is based on the photoconductivity of hydrogenated amorphous silicon in a coplanar electrode configuration. Excitation, with near UV/blue light, of a single-stranded DNA molecule tagged with the fluorophore 1-(3-(succinimidyloxycarbonyl)benzyl)-4-(5-(4-methoxyphenyl)oxazol-2-yl) pyridinium bromide (PyMPO), results in the emission of visible light. The emitted light is then converted into an electrical signal in the photodetector, thus allowing the optoelectronic detection of the DNA molecules. The detection limit of the present device is of the order of 1 × 10¹² molecules/cm² and is limited by the efficiency of the filtering of the excitation light. A surface density of 33.5 ± 4.0 pmol/cm² was measured for DNA covalently immobilized to the functionalized SiO₂ thin film and a surface density of 3.7 ± 1.5 pmol/cm² was measured for the complementary DNA hybridized to the bound DNA. The detection concept explored can enable on-chip electronic data acquisition, improving both the speed and the reliability of DNA microarrays.     

Biomimetic oxidase sensor based on functionalized surface of carbon nanotubes and iron prophyrins for catechol detection

A novel and highly stable biomimetic oxidase sensor system was designed for catehol detection. FePP used as biomimetic horseradish peroxidase (HRP) was immobilized onto modified multi-walled carbon nanotubes (MWCNTs). Functional groups such as –OH, –NH₂ and –COOH were introduced onto the surface of MWCNTs to provide biomimetic microenvironment for iron porphyrins (FePP). Stable biomimetic enzyme electrode has been developed to detect catechol as a simple, economical and efficient method. At optimal condition, the detection limit of OH-MWCNTs/FePP/Nafion was 3.754 × 10^− 6 M. After stored at − 4 °C for 35 days, the oxidation current value still maintained 98.3% of initial activity. In repetitive nature test, relative standard deviation (RSD) of oxidation current remained within 1.0% after ten consecutive measurements in the same concentration of catechol solution, while most of reported oxidase sensor was within 2.0% under the same condition.

     

Characteristics of complexation reaction of tetraphenylporphine with zinc(II) at solid-liquid interface

Fast complexation was found in the solid-liquid system using silica gel adsorbing Zn(ll) (ZnSiO₂) and organic solution of 5,10,15,20-tetraphenylporphine (H₂tpp). The reaction rate is mainly controlled by affinity of H₂tpp for silica gel, but the more complicated effect of the ZnSiO₂ surface is clarified.     

Glucose biosensor based on the room-temperature phosphorescence of TiO2/SiO2 nanocomposite

The direct immobilization of glucose oxidase (GOD) on TiO₂/SiO₂ nanocomposite and its application as glucose biosensor were investigated. The room-temperature phosphorescence of TiO₂/SiO₂ nanocomposite can be quenched by hydrogen peroxide (H₂O₂). The detection of glucose may be accomplished by monitoring the formation of hydrogen peroxide which generated in the oxidation process of glucose with the catalysis of GOD. To our surprise, by using a 96-hole polyporous plate accessory of fluorescence spectrophotometer, the biosensor exhibits excellent linear response to glucose concentrations ranging from 1.0 × 10⁻⁹ to 1.0 × 10⁻² M with a detection limit of 1.2 × 10⁻¹⁰ M. The TiO₂/SiO₂ nanocomposite can be used as both supporting material and signal transducer. The phosphorescence intensity and color of the biosensor change obviously and even could be observed with naked eyes by continuous addition of glucose. Based on the room-temperature phosphorescence of TiO₂/SiO₂ nanocomposite, a new method of solid substrate-room-temperature phosphorimetry (SS-RTP) for glucose determination is proposed. A glucose biosensor was fabricated with wide determination concentration range, low detection limit, high sensitivity, and fast response time. And the biosensor has been successfully applied to the determination of glucose in human blood serum. The coacervation of GOD enzyme and its interaction with TiO₂/SiO₂ nanocomposite enlarge the surface area and enhance the chemical stability of GOD. The nice biocompatibility, large surface area, good chemical stability and nontoxicity of the TiO₂/SiO₂ nanocomposite have made this material suitable for functioning as biosensor.     

Enhancement of biodiesel production in <Emphasis Type="Italic">Chlorella vulgaris</Emphasis> cultivation using silica nanoparticles

Silica nanoparticles were synthesized and used to enhance the gas-liquid mass transfer rate in a CO₂/water system. Using silica (SiO₂) and methyl-functionalized silica (SiO₂-CH₃) nanoparticles, the volumetric mass transfer coefficient (kLa) increased by 31 and 145%, respectively. SiO₂ and SiO₂-CH₃ nanoparticles were applied in Chlorella vulgaris culture to enhance the growth of microalgae for lipid production. The highest dry cell weight of C. vulgaris (1.49 g/L) was obtained by addition of SiO₂-CH₃ nanoparticles, compared to the control (0.48 g/L). Also, maximum productivity (1.005 g/L/day) of fatty acid methyl ester (FAME) in C. vulgaris culture was obtained by introducing SiO₂-CH₃ nanoparticles. Dry cell weight and FAME productivity increased 210 and 610%, respectively, with the addition of 0.2 wt% SiO₂-CH₃ nanoparticles.     

Sequential interactions of silver–silica nanocomposite (Ag–SiO2NC) with cell wall,metabolism and genetic stability of Pseudomonas aeruginosa,a multiple antibiotic‐resistant bacterium

The study was carried out to understand the effect of silver–silica nanocomposite (Ag–SiO₂NC) on the cell wall integrity, metabolism and genetic stability of Pseudomonas aeruginosa, a multiple drug‐resistant bacterium. Bacterial sensitivity towards antibiotics and Ag–SiO₂NC was studied using standard disc diffusion and death rate assay, respectively. The effect of Ag–SiO₂NC on cell wall integrity was monitored using SDS assay and fatty acid profile analysis, while the effect on metabolism and genetic stability was assayed microscopically, using CTC viability staining and comet assay, respectively. Pseudomonas aeruginosa was found to be resistant to β‐lactamase, glycopeptidase, sulfonamide, quinolones, nitrofurantoin and macrolides classes of antibiotics. Complete mortality of the bacterium was achieved with 80 μg ml^?1 concentration of Ag–SiO₂NC. The cell wall integrity reduced with increasing time and reached a plateau of 70% in 110 min. Changes were also noticed in the proportion of fatty acids after the treatment. Inside the cytoplasm, a complete inhibition of electron transport system was achieved with 100 μg ml^?1 Ag–SiO₂NC, followed by DNA breakage. The study thus demonstrates that Ag–SiO₂NC invades the cytoplasm of the multiple drug‐resistant P. aeruginosa by impinging upon the cell wall integrity and kills the cells by interfering with electron transport chain and the genetic stability.

Significance and Impact of Study

Although the synthesis, structural characteristics and biofunction of silver nanoparticles are well understood, their application in antimicrobial therapy is still at its infancy as only a small number of microorganisms are tested to be sensitive to nanoparticles. A thorough knowledge of the mode of interaction of nanoparticles with bacteria at subcellular level is mandatory for any clinical application. The present study deals with the interactions of Ag–SiO2NC with the cell wall integrity, metabolism and genetic stability of Pseudomonas aeruginosa, which would contribute substantially in strengthening the therapeutic applications of silver nanoparticles.     

Silicon dioxide in the defence induction of soybean against Spodoptera frugiperda

Silicon can increase the natural defence of plants against stresses including herbivorous insects. Silicon dioxide (SiO₂) is one of the forms of silicon, and despite its wide use in the industrial sector, its use in agriculture is still poorly adopted. The aim of this study was to evaluate the effectiveness of foliar application of SiO₂ in inducing defence against Spodoptera frugiperda in soybean. The experiments were conducted in a completely randomised design with four treatments (0%, 1%, 2.5%, and 5% of SiO₂). The effect on cannibalism, biological parameters (mortality, duration of the larval stage, duration of the pupal stage and pupal weight) and wear on the mandible of S. frugiperda were evaluated. The foliar silicon content was also determined. The supply of SiO₂ prolonged the duration of the larval and pupal stages of the S. frugiperda by 0.56 and 0.17 days for each 1% of SiO₂ applied, respectively. The use of SiO₂ at 5% increased the mortality rate of caterpillars in the larval stage by approximately 25%. There was no effect of SiO₂ application on cannibalism and weight of S. frugiperda pupae. There was wear on the caterpillars' jaws in the third and fourth instar at the highest SiO₂ concentration. The application of SiO₂ promoted greater accumulation of silicon in soybean leaves. It is concluded that the foliar application of SiO₂ affects the biological performance of S. frugiperda through the induction of defence in the soybean crop and presents itself as a promising strategy in integrated pest management programmes.     

One-Step Preparation and Fluorescence Enhancement Effect in SiO2/Eu2+ Doped with Ag Nanowires

Eu²⁺ single-doped SiO₂ (SiO₂/Eu²⁺) and Eu²⁺, Ag nanowires co-doped SiO₂ (SiO₂/Eu²⁺–Ag) luminescent nanomaterials were prepared by an efficient one-step sol–gel method. Their microstructure and optical properties were characterized, and the fluorescence enhancement of Eu²⁺ by Ag nanowires was investigated. The experimental results indicate that the average diameter of Ag nanowires doped is 12.5 nm, and the length–diameter ratio is 30. The Ag nanowires cannot only enhance the light absorption of SiO₂/Eu²⁺ in the range of 230–350 nm, but also reduce the fluorescence lifetime of Eu²⁺. More importantly, the emission intensity is enhanced after doping Ag nanowires, and the red shift phenomenon of the emission spectrum is observed, red shift occurs between 10 and 56 nm. The highest fluorescence intensity is accessed under the Ag doping concentration of 0.10 %. Additionally, the emission of SiO₂/Eu²⁺ with 0.10 % of Ag doping at 456 nm is 16 times stronger than that of pure SiO₂/Eu²⁺. The present results indicate that the fluorescence enhancement is attributed to the local field enhancement and the increased radiative decay rates induced by Ag nanowires.