Nanochannels Of Mesoporous Silica Research Articles

Tailoring molecular permeability of vertically-ordered mesoporous silica-nanochannel films on graphene for selectively enhanced determination of dihydroxybenzene isomers in environmental water samples

Herein we demonstrate a simple and rapid electrochemical method for selectively enhanced determination of catechol (CC) or hydroquinone (HQ) isomers in environmental water samples by tailoring the molecular permeability of vertically-ordered mesoporous silica-nanochannel films on electrochemically reduced graphene oxide (VMSF/ErGO). Such VMSF/ErGO composite film was fabricated on the gold electrode (AuE) surface using electrochemically assisted self-assembly approach. The as-prepared electrodes with surfactant micelles (SM) template inside silica nanochannels, designed as SM/VMSF/ErGO/AuE, possess hydrophobic hydrocarbon cores and show preferential response to CC via hydrophobic effect. After removing SM from silica nanochannels, the obtained VMSF/ErGO/AuE displays more sensitive response to HQ, which is due to the hydrogen bond effect between the silanol groups of silica walls and HQ. Given the potential-resolved and high electrocatalytic ability of ErGO, and molecular permeability and anti-fouling ability of VMSF, these two present sensors could detect CC and HQ in lake water with a low limit of detection (18 nM for CC and 16 nM for HQ), and a high sensitivity (0.33 μA/μM for CC and 0.37 μA/μM for HQ), without complicated sample pretreatment. Moreover, the proposed sensors provide a convenient, rapid and economic way for direct analysis of environmental water samples, exhibiting excellent long-term stability.

Diatom-inspired self-assembly for silica thin sheets of perpendicular nanochannels

HypothesisMultistage silicate self-organization into light-weight, high-strength, hierarchically patterned diatom frustules carries hints for innovative silica-based nanomaterials. With sodium silicate in a biomimetic sol-gel system templated by a tri-surfactant system of hexadecyltrimethylammonium bromide, sodium dodecylsulfate, and poly(oxyethylene-b-oxypropylene-b-oxyethylene) (P123), mesoporous silica nanochannel plates with perpendicular channel orientation are synthesized. The formation process, analogous to that of diatom frustules, is postulated to be directed by an oriented self-assembly of the block copolymer micelles shelled with charged catanionic surfactants upon silication. ExperimentsThe postulated formation process for the oriented silica nanochannel plates was investigated using time-resolved small-angle X-ray and neutron scattering (SAXS/SANS) and freeze fracture replication transmission electron microscopy (FFR-TEM). FindingsWith fine-tuned molar ratios of the anionic, cationic, and nonionic surfactants, the catanionic combination and the nonionic copolymer form charged, prolate ternary micelles in aqueous solutions, which further develop into prototype monolayered micellar plates. The prolate shape and maximized surfactant adsorption of the complex micelles, revealed from combined SAXS/SANS analysis, are of critical importance in the subsequent micellar self-assembly upon silicate deposition. Time-resolved SAXS and FFR-TEM indicate that the silicate complex micelles coalesce laterally into the prototype micellar nanoplates, which further fuse with one another into large sheets of monolayered silicate micelles of in-plane lamellar packing. Upon silica polymerization, the in-plane lamellar packing of the micelles further transforms to 2D hexagonal packing of vertically oriented silicate channels. The unveiled structural features and their evolution not only elucidate the previously unresolved self-assembly process of through-thickness silica nanochannels but also open a new line of research mimicking free-standing frustules of diatoms.

Direct electrochemical detection of 4-aminophenol in pharmaceuticals using ITO electrodes modified with vertically-ordered mesoporous silica-nanochannel films

Abstract 4-Aminophenol (4-AP) served as the drug intermediates has been widely used or found in pharmaceutical preparations. Therefore, direct and rapid determination of 4-AP content in pharmaceuticals is highly important for human health. In this work, we demonstrate a simple and fast electrochemical method for direct analysis of 4-AP in pharmaceuticals by using the indium tin oxide (ITO) electrode modified with vertically-ordered mesoporous silica-nanochannel films (VMSF). Arising from the vertically-aligned nanochannels and high porosity of VMSF, 4-AP could permeate the VMSF and transfer to the underlying electrode surface, ultimately giving rise to the electrochemical signal. By using the differential pulse voltammetry (DPV) method, the VMSF/ITO sensor was able to detect 4-AP in a wide linear range from 0.5 μM to 400 μM. The obtained limit of detection was calculated as 0.32 μM. Owing to the good anti-fouling and anti-interference ability of VMSF, direct analysis of 4-AP in pharmaceuticals was achieved, without any complex sample pretreatments.

Fast one-step fabrication of a vertically-ordered mesoporous silica-nanochannel film on graphene for direct and sensitive detection of doxorubicin in human whole blood

A vertically-ordered silica-nanochannel film on graphene was prepared by a one-step electrodeposition method for antifouling detection in human whole blood.

PH-modulated ion transport and amplified redox response of Keggin-type polyoxometalates through vertically-oriented mesoporous silica nanochannels

Cyclic voltammetry has been applied to characterize mass transport of a Keggin-type polyoxometalates ([SiW12O40]4-) through vertically-aligned mesoporous silica thin films in aqueous media. The results indicate a drastic influence of pH and the ionic strength which may be rationalized in terms of electrostatic interactions and confinement effects. Diffusion of such bulky anionic electroactive species is considerably restricted at pH values higher than the point of zero charge of the silica for which the walls of the nanochannels are negatively charged. On the other hand, the positive charge density generated in more acidic solutions favors the ingress of [SiW12O40]4- species through the mesochannels, enhancing considerably the electrochemical response, except at high ionic strength due to competition for the binding sites. The accumulation of POM anions into the silica films can be even promoted by functionalization of the silica surface with propylammonium groups. In summary, pH tuning induced gating of the ionic flux through the silica nanopores, which can be somewhat modulated by the ionic strength by varying the thickness of the electrical double layer generated at the silica walls surface.

Improved adhesion and performance of vertically-aligned mesoporous silica-nanochannel film on reduced graphene oxide for direct electrochemical analysis of human serum

Vertically-aligned mesoporous silica-nanochannel film (VMSF) has been demonstrated as effective anti-fouling and anti-inference layer for constructing electrochemical sensors. Conductive substrate with high electroactivity and adhesion is very important for improving the performance of VMSF based sensors in terms of stability, sensitivity and discrimination ability. We herein use reduced graphene oxide (rGO) sheets as conductive adhesive and electroactive layer between VMSF and glassy carbon electrode (GCE). VMSF can be stably grown on rGO layer by electrochemically assisted self-assembly method (EASA). Owing to the electroactive properties of rGO, VMSF/rGO/GCE is able to parallel or simultaneously detect small drugs or biomarkers with high sensitivity and distinct oxidation potential for different electroactive organic molecules. Combining the anti-fouling and anti-inference ability of VMSF, direct analysis of small drugs or biomarkers in complex biological (serum) sample is demonstrated.

Biomimetic Cu, Zn and Cu2 complexes inserted in mesoporous silica as catalysts for superoxide dismutation

Abstract Three CuZn-superoxide dismutase (SOD) functional mimics, [CuZn(dien)2(μ-Im)](ClO4)3 (1), [Cu2(dien)2(μ-Im)](ClO4)3 (2) (Im = imidazole, dien = diethylenetriamine), and [CuZn(salpn)Cl2] (3) (H2salpn = 1,3-bis(salicylideneamino)propane), were successfully inserted into the nanochannels of SBA-15 type mesoporous silica with retention of the silica mesostructure. X-ray absorption spectroscopic studies indicate that the encapsulated complexes keep unchanged the first-shell environment of Cu(II) and Zn(II) ions. Magnetic measurements suggest that the nanochannels constrain the geometry of the μ-imidazolate-Cu(II)2 core modifying the relative orientation of the two copper coordination planes. Confinement imposed by the silica nanochannels upon encapsulation of complexes 1 and 2 leads to stable hybrid materials at physiological pH with enhanced SOD activity relative to the free complexes. Unlike the imidazolato-bridged compounds, insertion of 3 in mesoporous silica leads to a less stable hybrid material exhibiting partial release into the aqueous solution and O2•− dismutation rate slower than the free complex. The covalent binding of a mononuclear Cu(dien)Im+ moiety to the mesoporous silica showed lower SOD activity than encapsulated imidazolato-bridged CuZn and Cu2 complexes. The results emphasize the positive effect of encapsulation on SOD activity of imidazolato-bridged dinuclear complexes.

Nanochannel-Confined Graphene Quantum Dots for Ultrasensitive Electrochemical Analysis of Complex Samples.

Herein, we present an electrochemical sensing platform based on nanochannel-confined graphene quantum dots (GQDs) that is able to detect a spectrum of small analytes in complex samples with high sensitivity. Vertically ordered mesoporous silica-nanochannel film (VMSF) is decorated on the supporting electrode, conferring the electrode with excellent antifouling and anti-interference properties through steric exclusion and electrostatic repulsion. The synthesized GQDs with different functionalities are confined in the nanochannels of VMSF through electrophoresis, serving as the recognition element and signal amplifier. Without the usual need of tedious pretreatment, ultrasensitive and fast detection of Hg2+, Cu2+, and Cd2+ (with limits of detection (LOD) of 9.8 pM, 8.3 pM, and 4.3 nM, respectively) and dopamine (LOD of 120 nM) in complex food (Hg2+-contaminated seafood), environmental (soil-leaching solution), and biological (serum) samples are realized as proof-of-concept demonstrations.

Supramolecular Switching of Ion-Transport in Nanochannels.

Noncovalent approaches to achieve smart ion-transport regulation in artificial nanochannels have garnered significant interest in the recent years because of their advantages over conventional covalent routes. Herein, we demonstrate a simple and generic approach to control the surface charge in mesoporous silica nanochannels by employing π-electron-rich charged motifs (pyranine-based donors) to interact with the surface of mesoporous silica modified with π-electron-deficient motifs (viologen-based acceptors) through a range of noncovalent forces, namely, charge-transfer, electrostatic, and hydrophobic interactions. The extent of each of these interactions was independently controlled by molecular design and pH, while employing them in a synergistic or antagonistic fashion to modulate the binding affinity of the charged motifs. This enabled the precise control of the surface charge of the nanochannels to achieve multiple ion-transport states.

Nanostructured Electrochemical Biosensors for Label-Free Detection of Water- and Food-Borne Pathogens.

The emergence of nanostructured materials has opened new horizons in the development of next generation biosensors. Being able to control the design of the electrode interface at the nanoscale combined with the intrinsic characteristics of the nanomaterials engenders novel biosensing platforms with improved capabilities. The purpose of this review is to provide a comprehensive and critical overview of the latest trends in emerging nanostructured electrochemical biosensors. A detailed description and discussion of recent approaches to construct label-free electrochemical nanostructured electrodes is given with special focus on pathogen detection for environmental monitoring and food safety. This includes the use of nanoscale materials such as nanotubes, nanowires, nanoparticles, and nanosheets as well as porous nanostructured materials including nanoporous anodic alumina, mesoporous silica, porous silicon, and polystyrene nanochannels. These platforms may pave the way toward the development of point-of-care portable electronic devices for applications ranging from environmental analysis to biomedical diagnostics.

Sintering-Resistant Nanoparticles in Wide-Mouthed Compartments for Sustained Catalytic Performance

Particle sintering is one of the most significant impediments to functional nanoparticles in many valuable applications especially catalysis. Herein, we report that sintering-resistant nanoparticle systems can be realized through a simple materials-design which maximizes the particle-to-particle traveling distance of neighbouring nanoparticles. As a demonstration, Pt nanoparticles were placed apart from each other in wide-mouthed compartments tailored on the surface of self-assembled silica nanosheets. These Pt nanoparticles retained their particle size after calcination at elevated temperatures because the compartment wall elongates the particle-to-particle traveling distance to preclude the possibility of sintering. Moreover, these Pt nanoparticles in wide-mouthed compartments were fully accessible to the environment and exhibited much higher catalytic activity for CO oxidation than the nanoparticles confined in the nanochannels of mesoporous silica. The proposed materials-design strategy is applicable not only to industrial catalysts operating in harsh conditions, but also opens up possibilities in developing advanced nanoparticle-based materials with sustained performance.

A High‐Sensitivity and Low‐Power Theranostic Nanosystem for Cell SERS Imaging and Selectively Photothermal Therapy Using Anti‐EGFR‐Conjugated Reduced Graphene Oxide/Mesoporous Silica/AuNPs Nanosheets

A high-sensitivity and low-power theranostic nanosystem that combines with synergistic photothermal therapy and surface-enhanced Raman scattering (SERS) mapping is constructed by mesoporous silica self-assembly on the reduced graphene oxide (rGO) nanosheets with nanogap-aligned gold nanoparticles (AuNPs) encapsulated and arranged inside the nanochannels of the mesoporous silica layer. Rhodamine 6G (R6G) as a Raman reporter is then encapsulated into the nanochannels and anti-epidermal growth factor receptor (EGFR) is conjugated on the nanocomposite surface, defined as anti-EGFR-PEG-rGO@CPSS-Au-R6G, where PEG is polyethylene glycol and CPSS is carbon porous silica nanosheets. SERS spectra results show that rGO@CPSS-Au-R6G enhances 5 × 10(6) magnification of the Raman signals and thus can be applied in the noninvasive cell tracking. Furthermore, it displays high sensitivity (detection limits: 10(-8) m R6G solution) due to the "hot spots" effects by the arrangements of AuNPs in the nanochannels of mesoporous silica. The highly selective targeting of overexpressing EGFR lung cancer cells (A549) is observed in the anti-EGFR-PEG-rGO@CPSS-Au-R6G, in contrast to normal cells (MRC-5). High photothermal therapy efficiency with a low power density (0.5 W cm(-2) ) of near-infrared laser can be achieved because of the synergistic effect by conjugated AuNPs and rGO nanosheets. These results demonstrate that the anti-EGFR-PEG-rGO@CPSS-Au-R6G is an excellent new theranostic nanosystem with cell targeting, cell tracking, and photothermal therapy capabilities.

Loading of an anti-cancer drug into mesoporous silica nano-channels and its subsequent release to DNA.

Mesoporous silica nano-channel (MCM-41) based molecular switching of a biologically important anticancer drug, namely, ellipticine (EPT) has been utilized to probe its efficient loading onto MCM-41, and its subsequent release to intra-cellular biomolecules, like DNA. By exploiting various spectroscopic techniques (like, steady state fluorescence, time-resolved fluorescence and circular dichroism), it has been shown that EPT can be easily translocated from MCM-41 to DNA without using any external stimulant. Blue emission of EPT in a polar aprotic solvent, i.e., dichloromethane (DCM), completely switches to green upon loading inside MCM-41 due to the conversion from a neutral to a protonated form of the drug inside nano-pores. Powder X-ray diffraction (PXRD), N2 gas adsorption and confocal fluorescence microscopy results confirm the adsorption of EPT inside the nano-pores of MCM-41. Here, the lysozyme (Lyz) protein has been utilized as a pore blocker of MCM-41 in order to prevent premature drug release. Interestingly, EPT is released to DNA even from the EPT-MCM-Lyz composite system, and results in intensification of green fluorescence. Electron microscopy results reveal the formation of a distinctive garland kind of morphology involving MCM-41 and DNA probably through non-covalent interactions, and this is believed to be responsible for the DNA assisted release of drug molecules from silica nano-pores. Confocal laser scanning microscopy (CLSM) imaging revealed that EPT-MCM is successfully internalized into the HeLa cervical cancer cells and localized into the nucleus. Cell viability assay results infer that EPT-MCM and EPT-MCM-Lyz showed much improved efficacy in HeLa cancer cells compared to free ellipticine.

Fabrication and characterization of mesoporous silica nanochannels inside the channels of anodic alumina membrane

Brij type surfactants (CnEOx) that have different chemical structures were used to fabricate 3D Mesoporous Silica Nanochannels (MSN) inside the channels of Anodic Alumina Membrane (AAM) under acidic conditions. The fabricated 3D MSN were characterized using TEM-ED, SEM, Small angle XRD, and N2 isotherm. Results revealed that the synthesis of ordered 3D cubic Im3m mesostructures can be formed with tunable pore diameters varied from 4.0 to 4.9nm that are partially affected with the length of ethylene oxide (EO) group in the template surfactant.

Salicylideneanilines encapsulated mesoporous silica functionalized gold nanoparticles: a low temperature calibrated fluorescent thermometer

A novel temperature responsive fluorescent sensor, encapsulated in the nanochannels of mesoporous silica functionalized with gold nanoparticles, was synthesized and studied for potential applications in cryogenic bio-detection and therapy fields.

Thermal Hydrogen Reduction for Synthesis of Gold Nanoparticles in the Nanochannels of Mesoporous Silica Composite

Gold nanoparticles (AuNPs) with small particle size have been difficult to be synthesized due to their strong agglomeration. Herein we report that the nanochannels of mesoporous silica synthesized from template sol-gel synthesis were utilized to prepare AuNPs by employing thermal hydrogen reduction. Mesoporous silica composite with an interpore distance of 4.1 nm was successfully fabricated as a thin film by an amphiphilic trinuclear gold(I) pyrazolate complex ([Au3Pz3]C10TEG) as a template. In contrast to calcination method of this composite and the bulk [Au3Pz3]C10TEG complex at 450ºC for 3 h, thermal hydrogen reduction at 250ºC for 2 h showed transmission electron microscope (TEM) images and diffraction pattern with smaller particle size (14.5 nm) and more homogenous distribution of AuNPs with up to 44% of the particle size in the range of 10 to 20 nm. The decreasing of average particle size in this new strategy indicated by the red-shifting of the surface plasmon resonance (SPR) band from 518 (AuNPs from the bulk [Au3Pz3]C10TEG complex) and 544 (calcination) to 558 nm.

Molecular ordering of the discotic liquid crystal HAT6 confined in mesoporous solids

An optical polarimetry study of the orientational order of a discotic liquid crystal (DLC), 2,3,6,7,10,11-hexakis(hexyloxy)triphenylene (HAT6), confined into parallel-aligned cylindrical nanochannels of mesoporous alumina, silica, and silicon membranes as a function of temperature and channel radius (3.4–21.0nm) is presented. In contrast to the bulk state, the birefringence resulting from the confined discotic liquid crystal, exhibits a continuous temperature evolution and is positive indicating a dominating face-on (homeotropic) type molecular ordering with respect to the channel walls. Pronounced hysteresis effects observed in the experiment are traced to different nucleation sites of the low-temperature phase upon cooling and the high-temperature phase upon heating. Deviations from the Gibbs–Thomson scaling of the phase transition temperature for channel diameters below 10nm are traced to splay distortions of the confined liquid crystal.

Synthesis of 2-substituted benzimidazoles and 2-aryl-1H-benzimidazoles using [Zn(bpdo)2·2H2O]2+/MCM-41 catalyst under solvent-free conditions

A cationic zinc(II) complex of the 2,2′-bipyridine-1,1′-dioxide ligand was prepared and loaded onto mesoporous silica nanochannels. The catalyst was characterized by powder X-ray diffraction, transmission electron microscopy, BET nitrogen adsorption–desorption method and FT-IR spectroscopy. The resulting material was used as a new catalyst in a novel and efficient procedure for the synthesis of 2-substituted benzimidazoles and 2-aryl-1H-benzimidazoles by simple condensation of O-phenylenediamine and carboxylic acids under solvent-free conditions.

PH Dictates the Release of Hydrophobic Drug Cocktail from Mesoporous Nanoarchitecture

Combination therapy has been a norm in clinical practice to effectively treat cancer. Besides polytherapy, nowadays, smart and nanobased drug carriers are extensively being explored to deliver drugs according to pathophysiological environment of diseases. In this regard, herein we designed intelligent mesoporous architecture, incorporating both combinational therapy with smart nanotechnology, to simultaneously deliver two highly hydrophobic chemotherapeutic drugs in response to extracellular and/or intracellular acidic environ of tumor. Novelty of the system lies in the employment of acid responsive ZnO QDs to clog not only the nanochannels of mesoporous silica, encapsulating one hydrophobic drug, but also exploitation of chelate forming propensity of another hydrophobic drug (curcumin) to load a significant quantity onto the surface of ZnO nanolids. Cell viability results revealed an extraordinarily high cytotoxic efficiency of that lethal drug cocktail even at a concentration as low as 3 μg/mL nanocarrier. We envision that this sophisticated nanocarrier, which utilizes both interior pore and exterior surface of nanolids for loading different hydrophobic guest molecules and their subsequent acid responsive release, will undoubtedly, illustrates its remarkable potential in targeted chemotherapy.

In situ incorporation of nickel nanoparticles into the mesopores of MCM-41 by manipulation of solvent–solute interaction and its activity toward adsorptive desulfurization of gas oil

In this contribution, different amounts of nickel were incorporated into the mesopores of MCM-41 via an in situ approach. A hydrophobic nickel precursor was incorporated into the nanochannels of mesoporous silica by manipulation of solvent–solute interaction. The synthesized material was characterized using X-ray diffraction, nitrogen physisorption, temperature programmed reduction, and transmission electron microscopy. The results implicate the formation of MCM-41 with well-ordered hexagonal structure and establish also the presence of nickel nanoparticles inside the nanochannels of mesoporous silica. Adsorptive desulfurization of gas oil was conducted using the nickel-incorporated MCM-41 samples. The effects of nickel concentration, temperature of process and feed flow rate on the desulfurization process were examined. The MCM-41 containing 6 wt.% of nickel had both the highest breakthrough sulfur adsorption capacity and total sulfur adsorption capacity, which were 0.69 and 1.67 mg sulfur/g adsorbent, respectively. The breakthrough sulfur adsorption capacity was almost regained after reductive regeneration of spent adsorbent. The obtained results suggest that the method applied for the synthesis of Ni y/MCM resulted in formation of well-dispersed, accessible and small nickel nanoparticles incorporated into the pores of MCM-41 which might be an advantage for adsorption of refractory sulfur compounds from low sulfur gas oil.