STXMPy: a new software package for automated region of interest selection and statistical analysis of XANES data

Background  

Soft X-ray spectromicroscopy based absorption near-edge structure analysis, is a spectroscopic technique useful for investigating sample composition at a nanoscale of resolution. While the technique holds great promise for analysis of biological samples, current methodologies are challenged by a lack of automatic analysis software e. g. for selection of regions of interest and statistical comparisons of sample variability.     

Quartz-crystal sensors for biosensing and chemical analysis

The principle and applications of quartz-crystal sensors based on the three basic concepts for mass, viscosity, and viscoelastic changes are reported. In the general discussion the realization of a resonant frequency-resonant resistance diagram is described in detail. As an example of application to mass sensing, gas sensing with a carbon-coated quartz crystal is reported. Determination of the blood coagulation factor is used as an example of the application to viscosity sensing. As an example of viscoelastic measurement, an ion-exchange polymer-coated quartz crystal is investigated to show that viscoelasticity changes more than mass in the transport process. The possibility of developing new biosensors and chemical sensors is discussed on the basis of these results.     

Polyaniline nanofibers: facile synthesis and chemical sensors

Polyaniline nanofibers with uniform diameters between 30 and 50 nm can be made in bulk quantities through a facile aqueous/organic interfacial polymerization method at ambient conditions. The nanofibers have lengths varying from 500 nm to several micrometers and form interconnected networks. Thin films made of the nanofibers have superior performance in both sensitivity and time response to vapors of acid (HCl) and base (NH3).     

Chalcogenide glass chemical sensors: Research and analytical applications

The paper is devoted to research and development in the field of chalcogenide glass chemical sensors for determination of heavy metal ions in solution. The overview of the solid-state scientific approach and research design of the sensing materials is followed by the original results of the analytical application of the chalcogenide glass sensors for laboratory analysis, industrial control and environmental monitoring.     

Solid-state chemical sensors: Atomistic models and research trends

After presenting a brief survey about thermodynamically and kinetically controlled sensing mechanisms, atomistic models and research trends of solid-state chemical sensors are discussed. Future work will involve new techniques of interface analysis, controlled two-dimensional physical chemistry at interfaces, new materials, new technologies, new microstructured devices and pattern recognition approaches.     

Piezoelectric microelectromechanical resonant sensors for chemical and biological detection

Piezoelectric microelectromechanical systems (MEMS) resonant sensors, known for their excellent mass resolution, have been studied for many applications, including DNA hybridization, protein-ligand interactions, and immunosensor development. They have also been explored for detecting antigens, organic gas, toxic ions, and explosives. Most piezoelectric MEMS resonant sensors are acoustic sensors (with specific coating layers) that enable selective and label-free detection of biological events in real time. These label-free technologies have recently garnered significant attention for their sensitive and quantitative multi-parameter analysis of biological systems. Since piezoelectric MEMS resonant sensors do more than transform analyte mass or thickness into an electrical signal (e.g., frequency and impedance), special attention must be paid to their potential beyond microweighing, such as measuring elastic and viscous properties, and several types of sensors currently under development operate at different resonant modes (i.e., thickness extensional mode, thickness shear mode, lateral extensional mode, flexural mode, etc.). In this review, we provide an overview of recent developments in micromachined resonant sensors and activities relating to biochemical interfaces for acoustic sensors.     

Fluorescent sensors for the detection of chemical warfare agents

Along with biological and nuclear threats, chemical warfare agents are some of the most feared weapons of mass destruction. Compared to nuclear weapons they are relatively easy to access and deploy, which makes them in some aspects a greater threat to national and global security. A particularly hazardous class of chemical warfare agents are the nerve agents. Their rapid and severe effects on human health originate in their ability to block the function of acetylcholinesterase, an enzyme that is vital to the central nervous system. This article outlines recent activities regarding the development of molecular sensors that can visualize the presence of nerve agents (and related pesticides) through changes of their fluorescence properties. Three different sensing principles are discussed: enzyme-based sensors, chemically reactive sensors, and supramolecular sensors. Typical examples are presented for each class and different fluorescent sensors for the detection of chemical warfare agents are summarized and compared.     

New polymeric chemical sensors for determination of lead ions

New polymeric electrochemical sensors for determining the content of lead were suggested. As the active substance of the polymeric membranes of the sensors was used N,N′-tetrabutyldipicolinamide, the compound exhibiting a high extractive capacity for heavy metal ions. The selectivity of the sensors with respect to lead ions in the presence of copper, cadmium, and zinc in a considerable excess was studied.     

Electrochemical properties of photocurable membranes for all-solid-state chemical sensors

The development of ion-selective electrodes with inner solid contact is described using photocurable acrylated polyurethane matrices and electron-ion exchanger (EI), which provides a reversible transition from electrical conductivity in the metal to ionic conductivity in the membrane phase. The application of a photocurable polymer matrix gives the possibility to use modern photolithographic techniques for the formation of all-solid-state chemical sensors. The influence of the polymer matrix and of the preparation of the membrane on the electro-chemical properties of calcium-selective membrane sensors is shown. For carbonate-selective membranes the possibility of improvement of electrochemical characteristics by incorporation of the anionic additive tetrakis (4-chlorophenyl) borate was studied.     

Electrochemical properties of photocurable membranes for all-solid-state chemical sensors

The development of ion-selective electrodes with inner solid contact is described using photocurable acrylated polyurethane matrices and electron-ion exchanger (EI), which provides a reversible transition from electrical conductivity in the metal to ionic conductivity in the membrane phase. The application of a photocurable polymer matrix gives the possibility to use modern photolithographic techniques for the formation of all-solid-state chemical sensors. The influence of the polymer matrix and of the preparation of the membrane on the electro-chemical properties of calcium-selective membrane sensors is shown. For carbonate-selective membranes the possibility of improvement of electrochemical characteristics by incorporation of the anionic additive tetrakis (4-chlorophenyl) borate was studied. Received: 14 June 1997 / Revised: 23 September 1997 / Accepted: 9 October 1997     

Optical chemical sensors for the detection of explosives and associated substances

The main analytical characteristics of optical chemical sensors for detecting the vapors and microparticles of explosives and associated substances are compared. The limits of detection, sensitivity, sensor setting time (response speed) and recovery time after the action of an analyte, and the selectivity of fluorescence sensors, chemiluminescence sensors, surface-enhanced Raman sensors, surface plasmon resonance sensors, absorption integrated optical waveguide sensors, waveguide interferometric sensors, and ring resonator based sensors. The effectiveness of the use of nanosized structures and bio- and nanostructured specific coatings in optical sensors is analyzed.     

Rational materials design of sorbent coatings for explosives: applications with chemical sensors

A series of chemoselective polymers had been designed and synthesized to enhance the sorption properties of polymer coated chemical sensors for polynitroaromatic analytes. To evaluate the effectiveness of the chemoselective coatings, a polynitroaromatic vapor test bed was utilized to challenge polymer coated surface acoustic wave (SAW) devices with different explosive vapors. Dinitrotoluene detection limits were determined to be in the <100 parts per trillion ranges. ATR-FTIR studies were used to determine the nature of the polymer-polynitroaromatic analyte interactions, and confirm the presence of hydrogen-bonding between polymer pendant groups and the nitro functional groups of polynitroaromatic explosive materials.     

Supramolecular complexes based on calixarenes: force field calculations and applications for chemical sensors

The inclusion of organic molecules to different calixarenes was investigated both experimentally and theoretically. Experimental data were obtained for various calixarenes of different thicknesses interacting with perchloroethylene, chloroform, benzene and toluene at different partial pressures and temperatures. The amount of included molecules was monitored by frequency responses of mass-sensitive bulk acoustic wave devices. To estimate ‘key-lock’ binding energies, the activation energy of desorption was determined experimentally from thermodesorption spectroscopy. The host/guest interaction energies were calculated theoretically with the TRIPOS force field approach which, in contrast to current quantum chemical approaches (MOPAC/AM1, MOPAC/PM3), gave satisfactory distance-dependent energy minima. Experimentally observed changes in the binding energies for the inclusion of C₂Cl₄, CHCl₃, CH₃C₅H₆ and C₆H₆ molecules in calixarenes agree surprisingly well with results with theoretical calculations.     

Rapid bioanalysis with chemical sensors: novel strategies for devices and artificial recognition membranes

The increasing importance of biological analytes in chemistry has triggered the development of a vast number of techniques for rapidly assessing them. Aside from microbiological test methods, a wide range of analytical sensor and detection methods are being developed. Within this article, we review the literature on this topic from the last five years, stressing two main aspects of method development. The first aspect is the design of novel analytical strategies and transducers to generate signals more sensitively, more rapidly and more efficiently. Most of the progress in this field has focused on electrochemical detection, although novel approaches to optical and mass-sensitive measurements have been reported. Second, we provide an overview of two main approaches to creating artificial interaction layers for sensors based on tailored interaction sites in polymeric or biomimetic systems. The most prominent of these approaches is (molecular) imprinting, where selectivity is achieved by directly templating a polymer material with the target analyte or a model compound, thus achieving biomimetic interaction sites within both thin films and particles.     

Searching for signals in the noise: metabolomics in chemical ecology

Chemically mediated interactions between organisms influence ecosystem structure, making it crucial for ecologists to understand these interactions. Advances in chemical ecology have often been closely linked to advances in analytical chemistry techniques. One recent development is the use of metabolomics to address questions in chemical ecology. Although metabolomics has much to offer this field, it is not without drawbacks. Here we consider how metabolomics techniques can supplement the traditional bioassay-guided fractionation approach to chemical ecology. We focus on specific examples that illustrate the advantages that metabolomic methods can provide over other methods in order to understand chemically mediated interactions between organisms.     

Molecular recognition: Supramolecular, polymeric and biomimetic coatings for chemical sensors and chromatographic columns

Complete control of the selective and reversible interaction of molecules from the gas or liquid phase at complementary recognition sites is of increasing interest for both basic science and practical applications. This recognition may occur at the surface or in the bulk of optimized chemically sensitive coatings. It is either monitored discontinuously by chromatography or continuously by a suitable sensor. The latter contains the optimized coating and converts the chemical information about concentrations of certain molecules by means of a certain transducer into an electronic signal. Generally speaking, these transducers form the essential part of ‘chemical sensors’; they monitor the molecular interactions at the chemically sensitive layer by changes in resistivity, impedance, mass, capacitance, work function, heat, electrochemical potential, optical thickness, or optical absorption in a certain spectral range. Three selected case studies of such molecular recognition devices which utilize supramolecular, polymeric, and biomimetic coatings are presented. Examples are given for both gas and liquid sensing devices. For simplification, because of its general applicability and its easy absolute calibration, particular emphasis is put on signal transduction via quartz crystal oscillators. The measurement principle is based on frequency changes which are directly correlated with mass changes and thus provide a particularly suitable signal transduction. The examples presented here concern systematic variations in the design of supramolecular cages, of selective interaction sites in polymeric matrices, and of covalently attached biomimetic recognition sites to monitor antibodies or enzyme interactions. Received: 11 August 1997 / Revised: 3 March 1998 / Accepted: 3 March 1998     

Molecular recognition: Supramolecular, polymeric and biomimetic coatings for chemical sensors and chromatographic columns

Complete control of the selective and reversible interaction of molecules from the gas or liquid phase at complementary recognition sites is of increasing interest for both basic science and practical applications. This recognition may occur at the surface or in the bulk of optimized chemically sensitive coatings. It is either monitored discontinuously by chromatography or continuously by a suitable sensor. The latter contains the optimized coating and converts the chemical information about concentrations of certain molecules by means of a certain transducer into an electronic signal. Generally speaking, these transducers form the essential part of ‘chemical sensors’; they monitor the molecular interactions at the chemically sensitive layer by changes in resistivity, impedance, mass, capacitance, work function, heat, electrochemical potential, optical thickness, or optical absorption in a certain spectral range. Three selected case studies of such molecular recognition devices which utilize supramolecular, polymeric, and biomimetic coatings are presented. Examples are given for both gas and liquid sensing devices. For simplification, because of its general applicability and its easy absolute calibration, particular emphasis is put on signal transduction via quartz crystal oscillators. The measurement principle is based on frequency changes which are directly correlated with mass changes and thus provide a particularly suitable signal transduction. The examples presented here concern systematic variations in the design of supramolecular cages, of selective interaction sites in polymeric matrices, and of covalently attached biomimetic recognition sites to monitor antibodies or enzyme interactions. Received: 11 August 1997 / Revised: 3 March 1998 / Accepted: 3 March 1998     

Surface engineering of one-dimensional tin oxide nanostructures for chemical sensors

Nanostructured materials are promising candidates for chemical sensors due to their fascinating physicochemical properties. Among various candidates, tin oxide (SnO₂) has been widely explored in gas sensing elements due to its excellent chemical stability, low cost, ease of fabrication and remarkable reproducibility. We are presenting an overview on recent investigations on 1-dimensional (1D) SnO₂ nanostructures for chemical sensing. In particular, we focus on the performance of devices based on surface engineered SnO₂ nanostructures, and on aspects of morphology, size, and functionality. The synthesis and sensing mechanism of highly selective, sensitive and stable 1D nanostructures for use in chemical sensing are discussed first. This is followed by a discussion of the relationship between the surface properties of the SnO₂ layer and the sensor performance from a thermodynamic point of view. Then, the opportunities and recent progress of chemical sensors fabricated from 1D SnO₂ heterogeneous nanostructures are discussed. Finally, we summarize current challenges in terms of improving the performance of chemical (gas) sensors using such nanostructures and suggest potential applications. Contains 101 references.