Cross-reactive Sensor Arrays Research Articles

Polyfluorophores on a DNA Backbone: Sensors of Small Molecules in the Vapor Phase

Vapors of small molecules are under widespread study in natural signalling, environmental monitoring, industrial quality control, and in medicine.[1–3] In the last few decades, advances in chemistry and material science have enabled the development of chemical sensors of such volatile organics,[4–7] in which conjugated polymers and cross-reactive chemical sensor arrays are the most widespread sensor types. Among them, optical vapor sensing arrays based on luminescence (including fluorescence) and absorbance have become essential.[8–13] In the recent past, colorimetric detection of volatile organics using crossreactive chemical sensors have been demonstrated in multiple applications.[14–16] Although absorbance–based methods for vapor detection have shown good success, fluorescence-based methods may offer some advantages, such as high sensitivity and low background. For example, the detection of vapors of nitroaromatics with conjugated polymers and bio-polymers has showed very high sensitivity.[17–23] Notably, much of the

Fluorescence Sensors for Lithium Ions and Small Peptides

Simple but powerful chemosensors were developed by taking advantage of self-assembly processes. First, we will describe a turn-on fluorescent sensor for the pharmacologically important lithium ion. The sensor can be used in purely aqueous solution, and it displays a very high selectivity for lithium over sodium and magnesium ions. It is based on a metallacrown receptor unit, which can be assembled in situ from simple building blocks. Furthermore, we will describe a cross-reactive sensor array for the detection of small peptides. The individual sensors of the array are formed by mixing metal complexes with fluorescent dyes.

A practical approach to optical cross-reactive sensor arrays

Supramolecular analytical chemistry has emerged as a new discipline at the interface of supramolecular and analytical chemistry. It focuses on analytical applications of molecular recognition and self-assembly. One of the important outcomes of the supramolecular analytical chemistry is the understanding of molecular aspects of sensor design, synthesis and binding studies of sensors while using rigorous methods of analytical chemistry as a touchstone to verify the viability of the supramolecular aspects of the sensor design. This critical review provides a simplified version of the chemometric procedures involved in realizing a successful analytical experiment that utilizes cross-reactive optical sensor arrays, and summarizes the current research in this field. This review also shows several examples of use of described chemometric methods for evaluation of chemosensors and sensor arrays. Thus, this review is aimed mostly at the readers who want to test their newly-developed chemosensors in cross-reactive arrays (169 references).

Editorial: Crystal‐Clear View of Chemistry

Editorial: Crystal‐Clear View of Chemistry

Cross‐Reactive Sensor Arrays for the Detection of Peptides in Aqueous Solution by Fluorescence Spectroscopy

A simple but powerful method for the sensing of peptides in aqueous solution has been developed. The transition-metal complexes [PdCl(2)(en)], [{RhCl(2)Cp*}(2)], and [{RuCl(2)(p-cymene)}(2)] were combined with six different fluorescent dyes to build a cross-reactive sensor array. The fluorescence response of the individual sensor units was based on competitive complexation reactions between the peptide analytes and the fluorescent dyes. The collective response of the sensor array in a time-resolved fashion was used as an input for multivariate analyses. A sensor array comprised of only six metal-dye combinations was able to differentiate ten different dipeptides in buffered aqueous solution at a concentration of 50 muM. Furthermore, the cross-reactive sensor could be used to obtain information about the identity and the quantity of the pharmacologically interesting dipeptides carnosine and homocarnosine in a complex biological matrix, such as deproteinized human blood serum. The sensor array was also able to sense longer peptides, which was demonstrated by differentiating mixtures of the nonapeptide bradykinin and the decapeptide kallidin.

Detection and classification of organophosphate nerve agent simulants using support vector machines with multiarray sensors.

The need for rapid and accurate detection systems is expanding and the utilization of cross-reactive sensor arrays to detect chemical warfare agents in conjunction with novel computational techniques may prove to be a potential solution to this challenge. We have investigated the detection, prediction, and classification of various organophosphate (OP) nerve agent simulants using sensor arrays with a novel learning scheme known as support vector machines (SVMs). The OPs tested include parathion, malathion, dichlorvos, trichlorfon, paraoxon, and diazinon. A new data reduction software program was written in MATLAB V. 6.1 to extract steady-state and kinetic data from the sensor arrays. The program also creates training sets by mixing and randomly sorting any combination of data categories into both positive and negative cases. The resulting signals were fed into SVM software for "pairwise" and "one" vs all classification. Experimental results for this new paradigm show a significant increase in classification accuracy when compared to artificial neural networks (ANNs). Three kernels, the S2000, the polynomial, and the Gaussian radial basis function (RBF), were tested and compared to the ANN. The following measures of performance were considered in the pairwise classification: receiver operating curve (ROC) Az indices, specificities, and positive predictive values (PPVs). The ROC Az) values, specifities, and PPVs increases ranged from 5% to 25%, 108% to 204%, and 13% to 54%, respectively, in all OP pairs studied when compared to the ANN baseline. Dichlorvos, trichlorfon, and paraoxon were perfectly predicted. Positive prediction for malathion was 95%.

A humidity sensor based on vapoluminescent platinum(II) double salt materials

The vapoluminescent characteristics of platinum(II) double salt materials in the presence of varying levels of relative humidity (RH) have been investigated. Luminescence spectra for three different platinum(II) double salt materials showed that the intensity and the wavelength maximum depend on the concentration of water vapor surrounding the material. Partial least squares (PLS) analysis of the data demonstrated that two of the double salts responded linearly to changes in RH. A single-channel dip probe sensor was constructed and used to evaluate changes in RH. Different methods for attaching the platinum(II) double salt material to the dip probe were also investigated. Simple adsorption of the material onto the probe produced a sensor with superior performance compared to a Teflon AF support matrix. The PLS analysis of simultaneous three-channel cross-reactive sensor array data from three different platinum(II) double salt materials yielded a much more reproducible RH sensor. In addition, the three-channel cross-reactive array produced a more linear PLS model compared to a single-channel sensor composed of a simulated mixture of the same three platinum(II) double salt materials.

Multishell microspheres with integrated chromatographic and detection layers for use in array sensors.

The development of miniaturized chromatographic systems localized within individual polymer microspheres and their incorporation into a bead-based cross-reactive sensor array platform is reported. The integrated chromatographic and detection concept is based on the creation of distinct functional layers within the microspheres. In this first example of the new methodology, complexing ligands have been selectively immobilized to create "separation" layers harboring an affinity for various metal cations. Additionally, a broadly responsive compleximetric dye is used to yield the "detection" layers that exhibit optical responses in the presence of a wide range of metal cations. Information concerning the identities and concentrations of solution-dissolved metal cations can be drawn from the temporal properties of the beads' optical responses. Varying the nature of the ligand in the separation shell yields a collection of cross-reactive sensing elements well-suited for use in array-based micrototal analysis systems. Accordingly, such beads have been incorporated into the "Electronic Taste Chip" platform and used for discriminating among aqueous metal cation solutions.

Characterization of a cross-reactive electronic nose with vapoluminescent array elements.

A three-channel cross-reactive sensor array based on vapoluminescent platinum(II) double salt materials has been characterized. Two arrays were studied, one consisting of [Pt(CN-cyclododecyl)4][Pt(CN)4] (1), [(phen)Pt(CN-cyclohexyl)2][Pt(CN)4] (2), and [Pt(CN-n-tetradecyl)4][Pt-(CN)4] (3) materials, where phen = 1,10-phenanthroline, and a second array that has compound 3 replaced by the mixed double salt material [(phen)Pt(CN-cyclododecyl)Cl)]2[(phen)Pt(CN-cyclododecyl)2]2[Pt(CN)4]3 (4). Compounds 2, 3 and 4 are characterized here for the first time. Inclusion of solvent vapors into these materials often leads to dramatic shifts in their solid-state absorption and luminescence spectra. In these studies the arrays were exposed to a set of 10 test solvent vapors to determine the ability of each cross-reactive array to give reproducible vapoluminescent spectra characteristic of each solvent vapor. It was discovered that temperature programming between solvent vapor exposures greatly improved the reproducibility of the luminescence spectra obtained. A statistical analysis of three-dimensional resolution factors between pairs of solvent clusters in principal component space supported this assertion. The success of the temperature programming protocol was limited by the thermal stability and the sensitivity to low background water vapor levels of some platinum(II) double salt materials. The ability of the cross-reactive sensor array to differentiate between two different solvent vapors over a large concentration range was also investigated. Acetone and methanol were found to occupy two distinct regions of the three-dimensional principal component space. Detection limits for acetone and methanol were estimated from the principal component analysis as 75 and 6 g/m3, respectively.

A chemical-detecting system based on a cross-reactive optical sensor array.

The vertebrate olfactory system has long been recognized for its extraordinary sensitivity and selectivity for odours. Chemical sensors have been developed recently that are based on analogous distributed sensing properties, but although an association between artificial devices and the olfactory system has been made explicit in some previous studies, none has incorporated comparable mechanisms into the mode of detection. Here we describe a multi-analyte fibre-optic sensor modelled directly on the olfactory system, in the sense that complex, time-dependent signals from an array of sensors provide a 'signature' of each analyte. In our system, polymer-immobilized dye molecules on the fibre tips give different fluorescent response patterns (including spectral shifts, intensity changes, spectral shape variations and temporal responses) on exposure to organic vapours, depending on the physical and chemical nature (for example, polarity, shape and size) of both the vapour and the polymer. We use video images of temporal responses of the multi-fibre tip as the input signals to train a neural network for vapour recognition. The system is able to identify individual vapours at different concentrations with great accuracy. 'Artificial noses' such as this should have wide potential application, most notably in environmental and medical monitoring.