Ratiometric pH-nanosensors based on rhodamine-doped silica nanoparticles functionalized with a naphthalimide derivative

This paper describes the preparation of two-dye-doped silica nanoparticles for ratiometric pH measurements in the biologically relevant pH-range. While a rhodamine derivative is embedded in a silica core and used as the reference, a pH-sensitive naphthalimide dye is immobilized on the previously amino-functionalized core through two different approaches. Either the naphthalimide’s carboxylic group is activated to a succinimidyl-ester to form an amide bond or the system can be built up via solid-phase organic synthesis in only two steps. Both types of nanosensors are characterized in terms of morphology (dynamic light scattering, transmission electron microscopy) and optical properties (steady-state fluorescence spectroscopy). In terms of application, e.g. reproducibility and handling of the synthesis, the first approach gave very good results with respect to size and size distribution and a pK_a value of 6.55 was found that is comparable to the free indicator dye in solution. The solid-phase organic synthesis method proves the possibility of covalent immobilization of naphthalimides to amino-functionalized surfaces, showing the stability of the polymeric substrate and achieving comparable results for pH sensing.     

Mixed alkanethiol self-assembled monolayers as substrates for microarraying applications

In current microarraying experiments, data quality is in large part determined by the quality of the spots that compose the microarray. Since many microarrays are made with contact printing techniques, microarray spot quality is fundamentally linked to the surface characteristics of the microarray substrate. In this work, surface coatings, consisting of self-assembled monolayers (SAMs) of mixed alkanethiol molecules, were used to control the surface properties of the microarray substrate. X-ray photoelectron spectroscopy and equilibrium contact angle measurements were performed in order to confirm the chemical content and wettability of these surface coatings. To test their performance in microarraying applications, sample microarrays were printed on these mixed alkanethiol films and then characterized with a noncontact visual metrology system and a fluorescence scanner. This work demonstrates that utilizing mixed alkanethiol SAMs as a surface coating provides spatially homogeneous surface characteristics that are reproducible across multiple microarray substrates as well as within a substrate. In addition, this paper demonstrates that these films are stable and robust as they can maintain their surface characteristics over time. Overall, it is demonstrated that SAMs of mixed alkanethiols serve as a useful surface coating, which enhances spot and therefore data quality in microarraying applications.     

Porous silicon surfaces: a candidate substrate for reverse protein arrays in cancer biomarker detection

This paper introduces a new substrate for reverse-phase protein microarray applications based on macroporous silicon. A key feature of the microarray substrate is the vastly surface enlarging properties of the porous silicon, which simultaneously offers highly confined microarray spots. The proof of principle of the reverse array concept was demonstrated in the detection of different levels of cyclin E, a possible cancer biomarker candidate which regulates G1-S transition and correlates with poor prognosis in different types of human cancers. The substrate properties were studied performing analysis of total cyclin E expression in human colon cancer cell lines Hct116 and SW480. The absence of unspecific binding and good microarray quality was demonstrated. In order to verify the performance of the 3-D textured macroporous surface for complex biological samples, lysates of the human tissue spiked to different levels with cell extract overproducing cyclin E (Hct116) were arrayed on the chip surface. The samples were spotted in a noncontact mode in 100 pL droplets with spots sizes ranged between 50 and 70 mum and spot-to-spot center distances 100 mum, allowing microarray spot densities up to 14 000 spots per cm(2). The different sample types of increasing complexities did not have any impact on the spot intensities recorded and the protein spots showed good homogeneity and reproducibility over the recorded microarrays. The data demonstrate the potential use of macroporous silicon as a substrate for quantitative determination of a cancer biomarker cyclin E in tissue lysates.     

An Anionic Interpenetrated Zeolite‐Like Metal–Organic Framework Composite As a Tunable Dual‐Emission Luminescent Switch for Detecting Volatile Organic Molecules

The luminescent MOF [(CH₃)₂NH₂]₂[(Zn₂O)L]?5 DMF (NENU‐519, NENU=Northeast Normal University) with a zeolite BCT topology was successfully synthesized. It is a rare example of a two‐fold interpenetrated framework with a zeolite topology. NENU‐519 demonstrates the ability to selectively adsorb cationic dyes. Furthermore we developed Rh6@NENU‐519 (Rh6=Rhodamine 6G) as a dual‐emitting sensor for probing different volatile organic molecules (VOMs) due to an energy transfer between L and the dye. The composite can be used to distinguish the isomers of o‐, m‐, and p‐xylene and ethylbenzene using the emission‐peak‐height ratios of L to the dye as detectable signals, in which the readout signals are involved in the interactions between the dye@MOF composite and the guest analytes. Moreover, Rh6@NENU‐519 can serve as a luminescent switch for the detection of different aromatic compounds, like benzene, benzene substituted with different groups, and pyridine. In other words, the Rh6@NENU‐519 composite can be used as molecular decoder of the structural information of different VOMs into recognizable luminescent signals. Hopefully this work will open a new corridor to develop luminescent guest@MOF composites as sensors for practical applications.     

Process optimization and characterization of thin films of SrFeO3-x by the pechini method

Nanostructured coatings have recently attracted increasing interest because of the possibilities of synthesizing materials with unique physical-chemical properties. Highly sophisticated surface related properties, such as optical, magnetic, electronic, catalytic, mechanical, chemical and tribological properties can be obtained by advanced nanostructured coatings, making them attractive for various industrial applications. In this report we describe our efforts at developing methodology for the fabrication of SrFeO_3-x based thin films using a modified Pechini method. Thin films of SrFeO_3-x were fabricated using spin coating and a drop coating method developed in-house on Al₂O₃ and Si- substrates. The films annealed at 600°C for one hour show a perovskite phase. The grain size increases with increase in annealing temperature. The influence of various variables such as metal to chelant ratio, drying control reagents, calcination conditions, substrate type and mode of film formation were studied using XRD, optical microscopy, SEM and AFM.     

Immobilization of ligands with precise control of density to electroactive surfaces

We report a broadly applicable surface chemistry methodology to immobilize ligands, proteins, and cells to an electroactive substrate with precise control of ligand density. This strategy is based on the coupling of soluble aminooxy terminated ligands with an electroactive quinone terminated monolayer. The surface chemistry product oxime is also redox active but at a different potential and therefore allows for real-time monitoring of the immobilization reaction. Only the quinone form of the immobilized redox pair is reactive with soluble aminooxy groups, which allows for the determination of the yield of reaction, the ability to immobilize multiple ligands at controlled densities, and the in-situ modulation of ligand activity. We demonstrate this methodology by using cyclic voltammetry to characterize the kinetics of a model interfacial reaction with aminooxy acetic acid. We also demonstrate the synthetic flexibility and utility of this method for biospecific interactions by installing aminooxy terminated FLAG peptides and characterizing their binding to soluble anti-FLAG with surface plasmon resonance spectroscopy. We further show this methodology is compatible with microarray technology by printing rhodamine-oxyamine in various size spots and characterizing the yield within the spots by cyclic voltammetry. We also show this methodology is compatible with cell culture conditions and fluorescent microscopy technology for cell biological studies. Arraying RGD-oxyamine peptides on these substrates allows for bio-specific adhesion of Swiss 3T3 Fibroblasts.     

Investigations on microstructure,composition and properties of PECVD TiNx-coatings

Nearly stoichiometric TiN_x-coatings have been deposited on different substrates using a gaseous reaction mixture of TiCl₄, N₂, H₂ and Ar in a pulsed d.c. plasma discharge. The influence of substrate temperature, plasma power density, argon partial pressure and type of substrate on chlorine content, texture and microstructure of the coatings has been investigated keeping constant the other parameters of the plasma enhanced chemical vapor deposition (PECVD) process. Microstructure has been characterized by scanning electron microscopy (SEM) fractographs of the coatings and by determination of texture. The chlorine content quantitatively determined from energy-dispersive X-ray spectra (EDX) using a chlorine containing mineral as standard decreases on an increase of substrate temperature or plasma power density. Texture changes from 〈200〉 to 〈111〉 and random and microstructure changes from columnar growth to granular for decreasing substrate temperature as well as decreasing plasma power density. Argon partial pressure does not affect the microstructure but the texture. The properties of the coatings are independent of type of substrate for higher plasma power densities. Oxygen present at the surface of the substrate stimulates the development of a texture at low plasma power densities.     

Double stabilization of silver molecular clusters in thin films

The evolution of spectral and luminescent properties of Ag-containing composite coatings prepared by liquid technique has been studied. Double stabilization allows forming thin oxide films containing luminescent small Ag_n (n?<?5) molecular clusters using the liquid technique. These clusters are non-stable intermediate products during the formation of Ag nanoparticles from the ions and neutral atoms. It was found that small luminescent Ag_n molecular clusters (n?<?5) formed in the solutions at the presence of polyvinylpyrrolidone (PVP) remain in PVP/metal nitrates composite coatings and in the calcined metal oxide coatings. Spatial separation of small Ag molecular clusters in the coatings by the oxide nanoparticles of ZnO and MgO prohibits silver clusters growth and non-luminescent silver nanoparticles formation and allows saving coatings’ luminescence properties during thermal treatment.

     

A sensitive probe for oxygen sensing in gas mixtures,based on room-temperature phosphorescence quenching

The dye Erythrosine B (which gives room-temperature phosphorescence, RTF) has been covalently bound to a silica-based amino-functionalized exchanger. The resulting material turned out to be extremely useful as a luminescent probe for oxygen. The photochemical properties and the analytical performance of the RTF probe have been studied by use of a gas flow-injection analysis system, which incorporates a convenient exponential dilution chamber for gas sample introduction. The possible origin of the non-linear Stern-Volmer quenching response observed is thoroughly discussed in terms of the quenching and lifetimes. The proposed sensing material is particularly suitable for measuring oxygen in gas mixtures at extremely low concentrations. The detection limit attained was 0.00006% (0.6 ppm) of oxygen in dry argon (making the system one of the more sensitive optosensors for oxygen published so far). A typical precision of ± 0.2%, at the 0.025% oxygen level, was achieved. Response times were less than 2 s for full signal change and no hysteresis effects were noticed. A possible mechanism for the observed oxygen RTF quenching in the new sensing material is proposed.     

Development of combinatorial chemistry methods for coatings: high-throughput weathering evaluation and scale-up of combinatorial leads

Combinatorial screening of materials formulations followed by the scale-up of combinatorial leads has been applied for the development of high-performance coating materials for automotive applications. We replaced labor-intensive coating formulation, testing, and measurement with a "combinatorial factory" that includes robotic formulation of coatings, their deposition as 48 coatings on a 9x12-cm plastic substrate, accelerated performance testing, and automated spectroscopic and image analysis of resulting performance. This high-throughput (HT) performance testing and measurement of the resulting properties provided a powerful set of tools for the 10-fold accelerated discovery of these coating materials. Performance of coatings is evaluated with respect to their weathering, because this parameter is one of the primary considerations in end-use automotive applications. Our HT screening strategy provides previously unavailable capabilities of (1) high speed and reproducibility of testing by using robotic automation and (2) improved quantification by using optical spectroscopic analysis of discoloration of coating-substrate structure and automatic imaging of the integrity loss of coatings. Upon testing, the coatings undergo changes that are impossible to quantitatively predict using existing knowledge. Using our HT methodology, we have developed several cost-competitive coatings leads that match the performance of more costly coatings. These HT screening results for the best coating compositions have been validated on the traditional scales of coating formulation and weathering testing. These validation results have confirmed the improved weathering performance of combinatorially developed coatings over conventional coatings on the traditional scale.     

Development of combinatorial chemistry methods for coatings: high-throughput adhesion evaluation and scale-up of combinatorial leads

Coupling of combinatorial chemistry methods with high-throughput (HT) performance testing and measurements of resulting properties has provided a powerful set of tools for the 10-fold accelerated discovery of new high-performance coating materials for automotive applications. Our approach replaces labor-intensive steps with automated systems for evaluation of adhesion of 8 x 6 arrays of coating elements that are discretely deposited on a single 9 x 12 cm plastic substrate. Performance of coatings is evaluated with respect to their resistance to adhesion loss, because this parameter is one of the primary considerations in end-use automotive applications. Our HT adhesion evaluation provides previously unavailable capabilities of high speed and reproducibility of testing by using a robotic automation, an expanded range of types of tested coatings by using the coating tagging strategy, and an improved quantitation by using high signal-to-noise automatic imaging. Upon testing, the coatings undergo changes that are impossible to quantitatively predict using existing knowledge. Using our HT methodology, we have developed several coatings leads. These HT screening results for the best coating compositions have been validated on the traditional scales of coating formulation and adhesion loss testing. These validation results have confirmed the superb performance of combinatorially developed coatings over conventional coatings on the traditional scale.     

Characteristics of dye-impregnated tetraethylorthosilane (TEOS) derived sol-gel coatings

An investigation has been carried out on a cross-comparison study into several sol-gel coatings, impregnated with a pH-sensitive fluorescent dye, to determine their optimum characteristics, with the aim of their application as thin film sensor elements in fibre optic chemical sensors. In this test of the coatings, they were applied to standard, cleaned microscope slides and several characteristics, such as the ability of the sol to wet the glass substrate and the optical clarity of the subsequent coating were investigated and found to depend mainly on the water: tetraethylorthosilane (H₂O: TEOS) ratio used in their preparation but also on the extent of aging and the level of catalyst used. It was found that thicker coatings could be created through the use of suitable chemical additives in the preparation process.     

Luminescent copolymers for applications in multicolor‐light‐emitting devices

Light‐emitting diodes based on organic materials [organic light‐emitting diodes (OLEDs)] have attracted much interest over the past decade. Several different attempts have been made to realize multicolor OLEDs. This article describes a new approach based on energy transfer in a donor/acceptor system. A copolymer containing both donor and acceptor compounds as comonomer units is prepared. The polymer consists of a derivative of a luminescent dye [4‐dicyanmethylene‐2‐methyl‐6‐4H‐pyran (DCM); acceptor compound], which is copolymerized with fluorene (donor compound) to combine the properties of an electroactive polymer with a highly luminescent dye. Photochemical processing is achieved by UV irradiation of this copolymer in the presence of gaseous trialkylsilanes. This reagent selectively saturates the C?C bonds in the DCM comonomer units while leaving the fluorene units essentially unaffected. As a result of the photochemical process, the red electroluminescence of the acceptor compound vanishes, and the blue‐green electroluminescence from the polyfluorene units is recovered. Compared with previous approaches based on polymer blends, this copolymer approach avoids problems associated with phase‐separation phenomena in the active layer of OLEDs. © 2006Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4317–4327, 2006     

Optical behaviour of pH detectors based on sol-gel technology

Acidity is an outstanding parameter that affect the correct preservation of most part of materials engaged in artworks and heritage objects. In spite of the new generation of advanced analytical devices, the conservation/heritage management sector claims for some kind of simple, robust and low-cost device to monitor environmental acidity wherever necessary. The purpose of this paper is to offer a suitable alternative for the estimation of environmental acidity by means of detectors to be used without electrodes, solutions, pH meters, wires or batteries.Doped sol-gel thin coatings have been used as transductors for producing pH detectors. The coatings consist of a partially densified polysiloxane network and an organic dye sensitive to pH changes. The siloxane network behaves as a host for immobilisation of the dye molecules, in such a way that chemical-optical properties of the dye are preserved as far as possible. The transductors were applied on common glass substrates by dipping. Further heat-treatment allows the coating partial densification.The optical response of the detectors was analysed by VIS absorption spectroscopy, since a change of colour took place when the detectors were submitted to different pH buffered solutions. With the aim to investigate their optical behaviour as a function of pH, several experimental measurements were undertaken: absorption intensity; maximum spectral wavelength; colour coordinates; colour purity percentages. Time response and memory effect were also studied. The detector operation conditions for monitoring environmental acidity both indoor and outdoor are discussed.     

Preparation of amino-functionalized mesoporous silica thin films with highly ordered large pore structures

Highly ordered amino-functionalized mesoporous silica thin films have been directly synthesized by co-condensation of tetraethoxysilane (TEOS) and 3-aminopropyltriethoxysilane (APTES) in the presence of triblock copolymer Pluronic P123 surfactant species under acidic conditions by sol-gel dip-coating. The effect of the sol aging on thin films organization is systematically studied, and the optimal sol aging time is obtained. The amino-functionalized mesoporous silica thin films exhibit a long-range ordering of 2D hexagonal (p6mm) mesostructure with a large pore size of 8.3 nm, a large Brunauer–Emmett–Teller (BET) specific surface area of 680 m² g⁻¹ and a large pore volume of 1.06 cm³ g⁻¹ following surfactant extraction as demonstrated by X-ray diffraction (XRD), Transmission electron microscope (TEM), and physical adsorption techniques. Based on BET surface area and weight loss, the surface coverage of amino-groups for the amino-functionalized mesoporous silica thin films is calculated to be 3.2 amino-groups per nm². Moreover, the functionalized thin films display improved properties for immobilization of cytochrome c in comparison with pure-silica mesoporous thin films.     

Construction of N-glycan microarrays by using modular synthesis and on-chip nanoscale enzymatic glycosylation

An effective chemoenzymatic strategy is reported that has allowed the construction, for the first time, of a focused microarray of synthetic N-glycans. Based on modular approaches, a variety of N-glycan core structures have been chemically synthesized and covalently immobilized on a glass surface. The printed structures were then enzymatically diversified by the action of three different glycosyltransferases in nanodroplets placed on top of individual spots of the microarray by a printing robot. Conversion was followed by lectin binding specific for the terminal sugars. This enzymatic extension of surface-bound ligands in nanodroplets reduces the amount of precious glycosyltransferases needed by seven orders of magnitude relative to reactions carried out in the solution phase. Moreover, only those ligands that have been shown to be substrates to a specific glycosyltransferase can be individually chosen for elongation on the array. The methodology described here, combining focused modular synthesis and nanoscale on-chip enzymatic elongation, could open the way for the much needed rapid construction of large synthetic glycan arrays.     

Morphology-controlled assembly of ZnO nanostructures: a bioinspired method and visible luminescence

In a bioinspired methodology, positively charged polypeptides and polyamines directly catalyse ZnO mineralization under "green" conditions of room temperature and neutral pH. The polyamines not only act as mineralizing agents for the formation of ZnO nanoparticles, but also self-assemble the nanoparticles to form spindle-like morphologies at these very ambient conditions. Both the directional growth of ZnO and its luminescent property have a pH dependency. At higher pH, the ZnO shape changes to a rodlike morphology that exhibits green photoluminescence with different intensity than that for ZnO spindles.     

In situ and real-time visualisation of oxygen distribution in DMFC using a porphyrin dye compound

A luminescent porphyrin dye film has been coated onto a transparent separator on the cathode side of a direct methanol fuel cell (DMFC) to visualise clearly oxygen distribution under operating conditions by analysing emission from the dye.     

A Luminescent Dye@MOF Platform: Emission Fingerprint Relationships of Volatile Organic Molecules

Self‐assembly of luminescent moieties into porous metal–organic frameworks (MOFs) has generated many luminescent platforms for probing volatile organic molecules (VOMs). However, most of those explored thus far have only been based on the luminescence intensity of one transition, which is not efficient for probing different VOMs. We have synthesized a luminescent MOF material containing 1D nanotube channels, and further developed a luminescent dye@MOF platform to realize the probing of different VOMs by tuning the energy transfer efficiency between two different emissions. The dye@MOF platform exhibits excellent fingerprint correlation between the VOM and the emission peak‐height ratio of ligand to dye moieties. The dye@MOF sensor is self‐calibrating, stable, and instantaneous, thus the approach should be a very promising strategy to develop luminescent materials with unprecedented practical applications.     

Numerical Modeling of Thin Film Deposition in Expanding Thermal Plasma

Expanding thermal plasma (ETP) is a widely used technique for deposition of a thin layer of ceramic materials and metal oxide on a substrate for a wide range of applications including abrasion resistance, UV absorption, as well as conductive and optical coatings. The coating quality is found to be dependent on operating parameters as well as reactor designs. In this article, we have presented a CFD based model of the ETP process to simulate the deposition of silica-like coatings on a polycarbonate substrate. Along with the flow-thermal model of plasma jet expansion process, the study also reports the development of a simplified gas phase and surface reaction model to simulate the coating phenomena. The model has been used further to study the effect of various operating conditions on the coating thickness, viz. reactor pressure, reagent flow rate, distance of the substrate from the arc and substrate alignment.