Mesoporous materials in sensing: morphology and functionality at the meso-interface

Synthesis of Fumed-Pr-Pi-TCT as a Fluorescent Chemosensor for the Detection of Cyanide Ions in Aqueous Media

In this research, fumed silica scaffolds modified via treatment with (3-chloropropyl)-triethoxysilane, piperazine, and trichlorotriazine groups were deployed for the specific detection of cyanide ions, thus paving the way for the detection of environmental hazards and pollutants with high specificity. Fumed-propyl -piperazine-trichlorotriazine (fumed-Pr-Pi-TCT) was synthesized in three steps starting from fume silica. It was functionalized subsequently using 3-(choloropropyl)-trimethoxysilane, piperazine, and trichlorotriazine, and then, the product was characterized through several methods including Fourier-transform infrared spectroscopy (FTIR) spectrum, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Fumed-Pr-Pi-TCT was exposed as a nanoparticle sensor to a range of different anions in aqueous media. This novel sensor could detect cyanide ions as a hazardous material, with the limit of detection being 0.82 × 10−4 M.

Development of an Approach of High Sensitive Chemiluminescent Assay for Cystatin C Using a Nanoparticle Carrier

Cystatin C is an important cysteine protease inhibitor in the human body and is proposed as a new indicator of glomerular filtration rate for the detection of kidney damage. In this article, we report an ultra-sensitive, simple, and rapid chemiluminescence immunoassay method for cystatin C detection using functionalized mesoporous silica nanoparticles. After a three step hydrolysis, the amino-functionalized MSN encapsulating dye resulted in a hydrophobic environment for fixing the dye and amino groups for biological modification. The NaIO₄ immobilization method maintained the activity of the antibody notably well. The sandwich immunoassay using two monoclonal antibodies was chosen for its selectivity. The analysis demonstrated that the detection upper was 0.0029 ng/mL and linear relationship within the range of 0.0035-0.5 ng/mL (R ² = 0.9936). The relative standard deviation (RSD) for 11 parallel measurements of 0.25 ng/mL CysC was 4.7%. The automated chemiluminescence analyzer could detect 96 wells continuously. The results demonstrated that this method is ultra-sensitive, simple, and rapid for detecting cystatin C.

Electrochemical flow injection analysis for the rapid determination of reducing sugars in potatoes

Non-enzymatic electrochemical sensors for the monitoring of reducing sugars in foods has great potential as a rapid in-situ detection method. This development involved the assembly of a nanoporous platinum structure on a screen-printed carbon electrode (SPCE). The modified electrode was then employed as an amperometric sensing element in a flow injection analysis (FIA) manifold. The system was successfully applied to the rapid detection of reducing sugars in potatoes, without the need for sample preparation. Optimal signals were achieved in phosphate buffer (pH 7.4) at a flow rate of 0.5 mL min^-1 and an applied potential of 0.6 V. Experimental results demonstrated the sensor's long-term stability and high selectivity for reducing sugars. This method provides high sample throughput due to a rapid response time of less than five seconds. Reducing sugar values determined were in good agreement with those recorded using a commercially available enzymatic assay kit.

Nanosilica: Recent Progress in Synthesis, Functionalization, Biocompatibility, and Biomedical Applications

Silica nanoparticles (Si-NPs) are widely explored in biomedical applications due to their high surface area, excellent biocompatibility, and tunable pore size. The silica surface can be readily functionalized for wide range of applications such as cellular imaging, biosensing, and targeted drug delivery. This comprehensive review discusses different synthesis methodologies of Si-NPs and their surface functionalization with various functional groups. Nanosilica functionalization methods are discussed in detail, emphasizing their suitability for targeted drug delivery, cancer therapy, bioimaging, and biosensing. The toxicity assessment of nanosilica is also critically reviewed to get a clear focus before employing them for nanomedicine.

Effect of surfactant concentration on textural characteristics and biomineralization behavior of mesoporous bioactive glasses

We report mesoporous bioactive glasses (MBGs) with different pore architecture synthesized using the supramolecular chemical approach using acid assisted sol-gel method followed by evaporation induced self-assembly (EISA) process. The surfactant of non-ionic block co-polymer used in the present work act as structure directing agent (SDA) with varying amount, which brings different textural properties. As prepared glasses possess wormhole-like mesostructure with different textural characteristics and it varies with surfactant concentrations. The pristine MBGs have been characterized by various analytical techniques before and after immersing in simulated body fluid (SBF). The textural properties show non-monotonous variations with varying the surfactant concentrations. We have quantified the various structural species present in the glass sample by using local structural probe such as nuclear magnetic resonance technique. Invitro studies on the MBGs revealed the influence of textural characteristics on the formation of nano-crystalline hydroxycarbonated apatite (HCA) layer. The biodegradability is largely related to the pore architecture and it affects the biocompatibility as well as bone formation. In-vitro studies reveals that there are serious negative effects that have been observed in the case of larger pore sized samples due to rapid degradation. We found that MBG with pore sizes of few nano meters exhibit favorable biocompatibility in vitro behavior and found to be promising candidate in the field of biomaterials including tissue regeneration and drug storage.

Facile Fabrication of Large-Scale Porous and Flexible Three-Dimensional Plasmonic Networks

Assembling metallic nanoparticles and trapping target molecules within the probe volume of the incident light are important in plasmonic detection. Porous solid structures with three-dimensionally integrated metal nanoparticles would be very beneficial in achieving these objectives. Currently, porous inorganic oxides are being prepared under stringent conditions and further subjected to either physical or chemical attachment of metal nanoparticles. In this study, we propose a facile method to fabricate large-scale porous and flexible three-dimensional (3D) plasmonic networks. Initially, uncured polydimethylsiloxane (PDMS), in which metal ions are dissolved, diffuses spontaneously into the simple sugar crystal template via capillary action. As PDMS is cured, metal ions are automatically reduced to form a dense array of metal nanoparticles. After curing, the sugar template is easily removed by water treatment to obtain porous 3D plasmonic networks. We controlled the far-field scattering and near-field enhancement of the network by changing either the metal ion precursor or its concentration. To demonstrate the key advantages of our 3D plasmonic networks, such as simple fabrication, optical signal enhancement, and molecular trapping, we conducted sensitive Raman detection of several important molecules, including adenine, humidifier disinfectants, and volatile organic compounds.

Miniaturized solid-phase extraction of macrolide antibiotics in honey and bovine milk using mesoporous MCM-41 silica as sorbent

A simple and effective method of miniaturized solid-phase extraction (mini-SPE) was developed for the simultaneous purification and enrichment of macrolide antibiotics (MACs) (i.e. azithromycin, clarithromycin, erythromycin, lincomycin and roxithromycin) from honey and skim milk. Mesoporous MCM-41 silica was synthesized and used as sorbent in mini-SPE. Several key parameters affecting the performance of mini-SPE procedure were thoroughly investigated, including sorbent materials, amount of sorbent and elution solvents. Under the optimized condition, satisfactory linearity (r² > 0.99), acceptable precision (RSDs, 0.3-7.1%), high sensitivity (limit of detection in the range of 0.01-0.76 μg/kg), and good recoveries (83.21-105.34%) were obtained. With distinct advantages of simplicity, reliability and minimal sample requirement, the proposed mini-SPE procedure coupled with ultrahigh performance liquid chromatography and quadrupole time-of-flight tandem mass spectrometry could become an alternative tool to analyze the residues of MACs in complex food matrixes.

N-Doped Ordered Mesoporous Carbon Originated from a Green Biological Dye for Electrochemical Sensing and High-Pressure CO2 Storage

Herein, a series of nitrogen-doped ordered mesoporous carbons (NOMCs) with tunable porous structure were synthesized via a hard-template method with a green biological dye as precursor, under various carbonization temperatures (700-1100 °C). Compared with the ordered mesoporous silica-modified and unmodified electrodes, the use of electrodes coated by NOMCs (NOMC-700-NOMC-1100) resulted in enhanced signals and well-resolved oxidation peaks in electrocatalytic sensing of catechol and hydroquinone isomers, attributable to NOMCs' open porous structures and increased edge-plane defect sites on the N-doped carbon skeleton. Electrochemical sensors using NOMC-1000-modified electrode were fabricated and proved feasible in tap water sample analyses. The NOMCs were also used as sorbents for high-pressure CO2 storage. The NOMC with the highest N content exhibits the best CO2 absorption capacities of 800.8 and 387.6 mg/g at 273 and 298 K (30 bar), respectively, which is better than those of other NOMC materials and some recently reported CO2 sorbents with well-ordered 3D porous structures. Moreover, this NOMC shows higher affinity for CO2 than for N2, a benefit of its higher nitrogen content in the porous carbon framework.

Anti-CD155 and anti-CD112 monoclonal antibodies conjugated to a fluorescent mesoporous silica nanosensor encapsulating rhodamine 6G and fluorescein for sensitive detection of liver cancer cells

Sensitive detection of liver cancer cells using anti-CD155 and anti-CD112 monoclonal antibodies conjugated to ultrabright fluorescent mesoporous silica nanoparticles (FMSNs) encapsulating Rhodamine 6G and fluorescein was developed.

Spin-coated Au-nanohole arrays engineered by nanosphere lithography for a Staphylococcus aureus 16S rRNA electrochemical sensor

The nanopatterning of gold nanoparticle (AuNP) arrays on an indium tin oxide (ITO) electrode using efficient and low-cost methods is described. This process used nanosphere lithography (NSL) encompassing the deposition of monolayered Polystyrene (PS) followed by a convective self-assembly drop coating protocol onto the ITO substrate that further acted as the mask after the AuNP assembly. The results showed that spin-coating allowed AuNPs to follow the contour and adhere to the PS nanospheres. The final products, after etching the PS, generated a highly ordered Au-nanohole array on an ITO substrate. The Au-nanohole arrays on the ITO electrode provided a greater surface area and successfully enhanced the peak current of electrochemical measurements by 82% compared with bare ITO and was used to detect Staphylococcus aureus 16S rRNA hybridization. In contrast to non-templated AuNP structures, the Au-nanohole arrays on the ITO electrode contributed to an optimum sensitivity improvement in DNA hybridization detection by 23%, along with an impressive limit of detection (LOD) of 10 pM. The high specificity of this distinguished structure was also achieved in the hybridization measurements of multi-analyte pathogens. These findings indicate that the combination of PS nanosphere lithography, followed by the spin-coating of AuNPs, leads to an inexpensive and simple engineering process that effectively generates uniform Au-nanohole arrays on ITO, which provides a greater surface area to optimize the electrochemical performance of the DNA biosensor.

Simultaneous determination of epinephrine and dopamine by electrochemical reduction on the hybrid material SiO₂/graphene oxide decorated with Ag nanoparticles

This paper describes the synthesis, characterization and applications of a new hybrid material composed of mesoporous silica (SiO2) modified with graphene oxide (GO), SiO2/GO, obtained by the sol-gel process using HF as the catalyst. The hybrid material, SiO2/GO, was decorated with silver nanoparticles (AgNPs) with a size of less than 20 nanometres, prepared directly on the surface of the material using N,N-dimethylformamide (DMF) as the reducing agent. The resulting material was designated as AgNP/SiO2/GO. The Ag/SiO2/GO material was characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and high-resolution transmission electron microscopy (HR-TEM). A glassy carbon electrode modified with AgNP/SiO2/GO was used in the development of a sensitive electrochemical sensor for the simultaneous determination of epinephrine and dopamine employing electrocatalytic reduction using squarewave voltammetry. Well-defined and separate reduction peaks were observed in PBS buffer at pH 7. No significant interference was seen for primarily biological interferents such as uric acid and ascorbic acid in the detection of dopamine and epinephrine. Our study demonstrated that the resultant AgNP/SiO2/GO-modified electrode is highly sensitive for the simultaneous determination of dopamine and epinephrine, with the limits of detection being 0.26 and 0.27 μmol L(-1), respectively. The AgNP/SiO2/GO-modified electrode is highly selective and can be used to detect dopamine and epinephrine in a human urine sample.

Lanthanide complex-incorporated periodic mesoporous organosilica nanospheres with tunable photoluminescence

Functional DPA (N,N-bis(trimethoxysilylpropyl)-2,6-pyridine dicarboxamide) can be successfully incorporated into mesoporous silica frameworks of regular spherical morphology to accommodate photoluminescent rare-earth metal centres.

Recent advances in hybrid periodic mesostructured organosilica materials: opportunities from fundamental to biomedical applications

Periodic mesoporous organosilica nanostructures functionalized with various active functional groups: from design to biomedical applications.

Molecular imprinting science and technology: a survey of the literature for the years 2004-2011

Herein, we present a survey of the literature covering the development of molecular imprinting science and technology over the years 2004-2011. In total, 3779 references to the original papers, reviews, edited volumes and monographs from this period are included, along with recently identified uncited materials from prior to 2004, which were omitted in the first instalment of this series covering the years 1930-2003. In the presentation of the assembled references, a section presenting reviews and monographs covering the area is followed by sections describing fundamental aspects of molecular imprinting including the development of novel polymer formats. Thereafter, literature describing efforts to apply these polymeric materials to a range of application areas is presented. Current trends and areas of rapid development are discussed.

Hybrid materials science: a promised land for the integrative design of multifunctional materials

For more than 5000 years, organic-inorganic composite materials created by men via skill and serendipity have been part of human culture and customs. The concept of "hybrid organic-inorganic" nanocomposites exploded in the second half of the 20th century with the expansion of the so-called "chimie douce" which led to many collaborations between a large set of chemists, physicists and biologists. Consequently, the scientific melting pot of these very different scientific communities created a new pluridisciplinary school of thought. Today, the tremendous effort of basic research performed in the last twenty years allows tailor-made multifunctional hybrid materials with perfect control over composition, structure and shape. Some of these hybrid materials have already entered the industrial market. Many tailor-made multiscale hybrids are increasingly impacting numerous fields of applications: optics, catalysis, energy, environment, nanomedicine, etc. In the present feature article, we emphasize several fundamental and applied aspects of the hybrid materials field: bioreplication, mesostructured thin films, Lego-like chemistry designed hybrid nanocomposites, and advanced hybrid materials for energy. Finally, a few commercial applications of hybrid materials will be presented.

pH and ion strength modulated ionic species loading in mesoporous silica nanoparticles

Mesoporous silica nanoparticles (MSN) have emerged as appealing host materials to accommodate guest molecules for biomedical applications, and recently various methods have been developed to modulate the loading of guest molecules in the silica matrix. Herein, it was demonstrated that pH and ion strength showed great influence on the loading of charged species into the nanoparticles, taking MCM-41 as a host MSN model and methylviologen (MV(2+)) and 1,5-naphthalene disulfonate (NDS(2-)) as typical charged ionic guest molecules. As the pH increased from 3.0 to 8.0, the loading amount of MV(2+) increased gradually, while on the contrary, it decreased gradually for NDS(2-), for the solution pH changed the electrostatic interaction between the silica matrix and the ionic guest molecules. Additionally, the adding of NaCl reduced the electrostatic interaction, which resulted in a decreasing of the electrostatic rejection and electrostatic accumulation for the molecules carrying the same and the opposite charge to the particle respectively. Thus, pH and ion strength can be employed as simple approaches to modulate the loading of charged molecules and permselectivity in MSN. This work has a definite guidance function for molecule loading, transport modulation, controlled release as well as sensors based on MSN.

Soft templating strategies for the synthesis of mesoporous materials: inorganic, organic-inorganic hybrid and purely organic solids

With the discovery of MCM-41 by Mobil researchers in 1992 the journey of the research on mesoporous materials started and in the 21st century this area of scientific investigation have extended into numerous branches, many of which contribute significantly in emerging areas like catalysis, energy, environment and biomedical research. As a consequence thousands of publications came out in large varieties of national and international journals. In this review, we have tried to summarize the published works on various synthetic pathways and formation mechanisms of different mesoporous materials viz. inorganic, organic-inorganic hybrid and purely organic solids via soft templating pathways. Generation of nanoscale porosity in a solid material usually requires participation of organic template (more specifically surfactants and their supramolecular assemblies) called structure-directing agent (SDA) in the bottom-up chemical reaction process. Different techniques employed for the syntheses of inorganic mesoporous solids, like silicas, metal doped silicas, transition and non-transition metal oxides, mixed oxides, metallophosphates, organic-inorganic hybrids as well as purely organic mesoporous materials like carbons, polymers etc. using surfactants are depicted schematically and elaborately in this paper. Moreover, some of the frontline applications of these mesoporous solids, which are directly related to their functionality, composition and surface properties are discussed at the appropriate places.

A fluorescent and chemiluminescent difunctional mesoporous silica nanoparticle as a label for the ultrasensitive detection of cancer cells

A new kind of ultrabright fluorescent and chemiluminescent difunctional mesoporous silica nanoparticle (FCMSN) is reported. A luminescent dye, Rhodamine 6G or tris(2,2'-bipyridyl)dichlororuthenium(II) hexahydrate (Rubpy), is doped inside nanochannels of a silica matrix. The hydrophobic groups in the silica matrix avoid the leakage of dye from open channels. The amines groups on the surface of the FCMSN improve the modification performance of the nanoparticle. Because the nanochannels are isolated by a network skeleton of silica, fluorescence quenching based on the inner filter effect of the fluorescent dyes immobilized in nanochannels is weakened effectively. The Quantum Yield of obtained 90 nm silica particles was about 61%. Compared with the fluorescent core-shell nanoparticle, the chemiluminescence reagents can freely enter the nanoparticles to react with fluorescent dyes to create chemiluminescence. The results show that the FCMSN are both fluorescent labels and chemiluminescent labels. In biological applications, the NaIO(4) oxidation method was proven to be superior to the glutaraldehyde method. The amount of amino could affect the specificity of the FCMSN. The fluorescence microscopy imaging demonstrated that the FCMSN is viable for biological applications.

Mesoporous metal oxides by vapor infiltration and atomic layer deposition on ordered surfactant polymer films

Catalysis, chemical separations, and energy conversion devices often depend on well-defined mesoporous materials as supports or active component elements. Herein, we show that ordered assembled organic surfactant films can directly template porous inorganic solids with surface area exceeding 1000 m(2)/g by infusing the polymers with reactive inorganic vapors, followed by anneal. The specific surface area, pore size, chemical composition, and overall shape of the product material are tuned by choice of the polymer and precursor materials as well as the influsion and postinfusion treatment conditions. X-ray diffraction, infrared spectroscopy, and electron microscopy show that vapor infusion changes both the physical and chemical structure of the starting ordered polymer films, consistent with quantified trends in specific surface area and pore size distribution measured by nitrogen adsorption after film annealing. This method yields porous TiO(2) films, for example, that function as an anode layer in a dye-sensitized solar cell.

X-ray lithography and small-angle X-ray scattering: a combination of techniques merging biology and materials science

The advent of micro/nanotechnology has blurred the border between biology and materials science. Miniaturization of chemical and biological assays, performed by use of micro/nanofluidics, requires both careful selection of the methods of fabrication and the development of materials designed for specific applications. This, in turn, increases the need for interdisciplinary combination of suitable microfabrication and characterisation techniques. In this review, the advantages of combining X-ray lithography, as fabrication technique, with small-angle X-ray scattering measurements will be discussed. X-ray lithography enables the limitations of small-angle X-ray scattering, specifically time resolution and sample environment, to be overcome. Small-angle X-ray scattering, on the other hand, enables investigation and, consequently, adjustment of the nanostructural morphology of microstructures and materials fabricated by X-ray lithography. Moreover, the effect of X-ray irradiation on novel materials can be determined by use of small-angle X-ray scattering. The combination of top-down and bottom-up methods to develop new functional materials and structures with potential in biology will be reported.

Amine-functionalized SBA-15 with uniform morphology and well-defined mesostructure for highly sensitive chemosensors to detect formaldehyde vapor

Amine-functionalized SBA-15 with uniform morphology and well-defined mesostructure was prepared using a postgrafting route. The morphology, mesostructure, and functionality of the materials were characterized by scanning electron microscopy, transmission electron microscopy, small-angle X-ray scattering, nitrogen adsorption-desorption, Fourier transform infrared spectroscopy, and solid-state nuclear magnetic resonance spectroscopy techniques. The results show that hexagonal lamelliform SBA-15 with a uniform particle size and short vertical channels plays two significant roles in uniformly dispersing amine-functionalizing groups and effectively adjusting the loadings of the functional groups within the mesopore channels. To confirm the potential application of the hybrids in gas sensors, using amine-functionalized SBA-15 as a sensing material and a quartz crystal microbalance as a transducer, a parts per billion level formaldehyde sensor with high sensitivity (response time about 11 s, recovery time about 15 s) and good chemoselectivity was achieved. This material holds great potential in the area of rapid, sensitive, and highly convenient formaldehyde detection.

Time-resolved indirect nanoplasmonic sensing spectroscopy of dye molecule interactions with dense and mesoporous TiO2 films

Indirect nanoplasmonic sensing (INPS) is an experimental platform exploiting localized surface plasmon resonance (LSPR) detection of processes in nanomaterials, molecular assemblies, and films at the nanoscale. Here we have for the first time applied INPS to study dye molecule adsorption/impregnation of two types of TiO(2) materials: thick (10 μm) mesoporous films of the kind used as photoanode in dye-sensitized solar cells (DSCs), with particle/pore size in the range of 20 nm, and thin (12-70 nm), dense, and flat films. For the thick-film experiments plasmonic Au nanoparticles were placed at the hidden, internal interface between the sensor surface and the mesoporous TiO(2). This approach provides a unique opportunity to selectively follow dye adsorption locally in the hidden interface region inside the material and inspires a generic and new type of nanoplasmonic hidden interface spectroscopy. The specific DSC measurement revealed a time constant of thousands of seconds before the dye impregnation front (the diffusion front) reaches the hidden interface. In contrast, dye adsorption on the dense, thin TiO(2) films exhibited much faster, Langmuir-like monolayer formation kinetics with saturation on a time scale of order 100 s. This new type of INPS measurement provides a powerful tool to measure and optimize dye impregnation kinetics of DSCs and, from a more general point of view, offers a generic experimental platform to measure adsorption/desorption and diffusion phenomena in solid and mesoporous systems and at internal hidden interfaces.

Catalytic applications of mesoporous silica-based materials

Mesoporous materials featuring high surface areas (>600m2g−1), narrow pore size distribution and tuneable pores diameters (>2nm), have attracted a great deal of attention in recent years due to their promising properties and applications in various areas including adsorption, separation, drug delivery, sensing and catalysis. Catalytic applications of such materials have been extended to numerous processes and reactions which range from acid catalysis (alkylations, acylations, esterifications, biodiesel production, etc.) to redox chemistries (oxidation of alcohols, alkenes, sulfides and hydrogenations of acids, aldehydes and ketones and alkenes/alkynes). In this chapter, we aim to provide an overview on the utilisation of mesoporous materials in heterogeneous catalysis, with special emphasis on acid and redox catalysed processes.

Multifunctional magnetic mesoporous silica nanocomposites with improved sensing performance and effective removal ability toward Hg(II)

In the present work, a multifunctional inorganic-organic hybrid nanomaterial (MMS-Py) was prepared by the immobilization of a pyrene-based receptor (Py) within the channels of magnetic mesoporous silica nanocomposites (MMS), and characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, N(2) adsorption/desorption, superconducting quantum interference device, and photoluminescence spectra. This multifunctional nanomaterial exhibits superparamagnetic behavior, ordered mesoporous characteristics, and significantly improved fluorescence sensing properties that allow for highly sensitive and reproducible Hg(2+) detection. The fluorogenical responses of MMS-Py are stable over a broad pH range. A detection limit of 1.72 ppb is obtained, which is 2 orders of magnitude lower than that based on bulk mesoporous materials. Additionally, this nanomaterial shows high performance in convenient magnetic separability and efficient removal of Hg(2+). These results indicate that these multifunctional nanocomposites may find potential applications for simple detection and easy removal of Hg(2+) in biological, toxicological, and environmental areas.