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The development of a low-cost, sensitive colorimetric sensor array for the detection and identification of volatile organic compounds (VOCs) is reported. Using an array composed of chemoresponsive dyes, enormous discriminatory power is possible in a simple device that can be imaged easily with an ordinary flatbed scanner. Excellent differentiation of closely related organic compounds can be achieved, and a library of 100 VOCs is presented. The array discriminates among VOCs by probing a wide range of intermolecular interactions, including Lewis acid/base, Bronsted acid/base, metal ion coordination, hydrogen bonding, and dipolar interactions. Importantly, by proper choice of dyes and substrate, the array is essentially nonresponsive to changes in humidity.

Acceptable air pollutant concentration limits for sensitive artwork are generally at or below a few ppb: this is only ∼1% of the permissible exposure limits for humans. Monitoring pollutants at such low levels is an exceptional challenge, especially to do so in a cost-effective fashion for a large number of locations and microenvironments (e.g., every display case in a museum). To meet this challenge, we have extended our portable “optoelectronic nose,” by using new sensor array chemistry to develop cumulative colorimetric sensor arrays with dosimetric sensitivities that are dramatically better than commercial sensor tubes. The color changes of each sensor in a disposable printed array produce a composite response to volatiles. Using cell phone camera imaging, we have made field trials to monitor pollutant exposure of artwork from the Walt Disney Animation Research Library during shipping to and exhibition in Beijing. This exhibition, “Drawn from Life: the Art of Disney Animation Studios,” featured animation drawings, story sketches, layouts, and concept art spanning the 90 years of the Disney Animation Studio’s history. Sensor arrays monitored exterior and interior environments of passe-partout artwork frames during exhibition and inside shipping crates during transport providing quantitative information on oxidant, aldehyde, and sulfide pollutant exposure. [ABSTRACT FROM AUTHOR]

A colorimetric sensor array has been designed for the identification of and discrimination among aldehydes and ketones in vapor phase. Due to rapid chemical reactions between the solid-state sensor elements and gaseous analytes, distinct color difference patterns were produced and digitally imaged for chemometric analysis. The sensor array was developed from classical spot tests using aniline and phenylhydrazine dyes that enable molecular recognition of a wide variety of aliphatic or aromatic aldehydes and ketones, as demonstrated by hierarchical cluster, principal component, and support vector machine analyses. The aldehyde/ketone-specific sensors were further employed for differentiation among and identification of ten liquor samples (whiskies, brandy, vodka) and ethanol controls, showing its potential applications in the beverage industry. [ABSTRACT FROM AUTHOR]

Forensic identification of batches of homemade explosives (HME) poses a difficult analytical challenge. Differentiation among peroxide explosives is reported herein using a colorimetric sensor array and handheld scanner with a field-appropriate sampling protocol. Clear discrimination was demonstrated among twelve peroxide samples prepared from different reagents, with a classification accuracy ＞98%. [ABSTRACT FROM AUTHOR]

Rapid identification of both species and even specific strains of human pathogenic bacteria grown on standard agar has been achieved from the volatiles they produce using a disposable colorimetric sensor array in a Petri dish imaged with an inexpensive scanner. All 10 strains of bacteria tested, including Enterococcus faecalis and Staphylococcus aureus and their antibiotic-resistant forms, were identified with 98.8% accuracy within 10 h, a clinically important time frame. Furthermore, the colorimetric sensor arrays also proved useful as a simple research tool for the study of bacterial metabolism and as an easy method for the optimization of bacterial production of fine chemicals or other fermentation processes. [ABSTRACT FROM AUTHOR]

While the complexes between boronic acids and diols have been studied for decades, researchers continue to design new and interesting methods to use these interactions to produce saccharide sensors that are more sensitive and selective. Herein we discuss how the use of pattern-based colorimetric arrays from a collection of crossreactive sensors have been developed as new differential sensing platforms for sugars and related saccharides. [ABSTRACT FROM AUTHOR]

We have developed a simple colorimetric sensor array that detects a wide range of volatile analytes and then applied it to the detection of toxic gases. The sensor consists of a disposable array of cross-responsive nanoporous pigments with colours that are changed by diverse chemical interactions with analytes. Although no single chemically responsive pigment is specific for any one analyte, the pattern of colour change for the array is a unique molecular fingerprint. Clear differentiation among 19 different toxic industrial chemicals (TICs) within two minutes of exposure at concentrations immediately dangerous to life or health were demonstrated. Based on the colour change of the array, quantification of each analyte was accomplished easily, and excellent detection limits were achieved, generally below the permissible exposure limits. Different TICs were identified readily using a standard chemometric approach (hierarchical clustering analysis), with no misclassifications over 140 trials. [ABSTRACT FROM AUTHOR]

Triacetone triperoxide (TATP), one of the most dangerous primary explosives, has emerged as an explosive of choice for terrorists in recent years. Owing to the lack of UV absorbance, fluorescence, or facile ionization, TATP is extremely difficult to detect directly. Techniques that are able to detect generally require expensive instrumentation, need extensive sample preparation, or cannot detect TATP in the gas phase. Here we report a simple and highly sensitive colorimetric sensor for the detection of TATP vapor with semiquantitative analysis from 50 ppb to 10 ppm. By using a solid acid catalyst to pretreat a gas stream, we have discovered that a colorimetric sensor array of redox sensitive dyes can detect even very low levels of TATP vapor from its acid decomposition products (e.g., H2O2) with limits of detection (LOD) below 2 ppb (i.e., <0.02% of its saturation vapor pressure). Common potential interferences (e.g., humidity, personal hygiene products, perfume, laundry supplies, volatile organic compounds, etc.) do not generate an array response, and the array can also differentiate TATP from other chemical oxidants (e.g., hydrogen peroxide, bleach, tert-butylhydroperoxide, peracetic acid). [ABSTRACT FROM AUTHOR]

The analysis of complex mixtures presents a difficult challenge even for modem analytical techniques, and the ability to discriminate among closely similar such mixtures often remains problematic. Coffee provides a readily available archetype of such highly multicomponent systems. The use of a low-cost, sensitive colorimetric sensor array for the detection and identification of coffee aromas is reported. The color changes of the sensor array were used as a digital representation of the array response and analyzed with standard statistical methods, including principal component analysis (PCA) and hierarchical clustering analysis (HCA). PCA revealed that the sensor array has exceptionally high dimensionality with 18 dimensions required to define 90% of the total variance. In quintuplicate runs of 10 commercial coffees and controls, no confusions or errors in classification by HCA were observed in 55 trials. In addition, the effects of temperature and time in the roasting of green coffee beans were readily observed and distinguishable with a resolution better than 10 °C and 5 mm, respectively. Colonmetric sensor arrays demonstrate excellent potential for complex systems analysis in real-world applications and provide a novel method for discrimination among closely similar complex mixtures. [ABSTRACT FROM AUTHOR]

A disposable, low-cost colorimetric sensor array has been created by pin-printing onto a hydrophilic membrane 16 chemically responsive nanoporous pigments that are comprised of indicators immobilized in an organically modified silane (ormosil). The array has been used to detect and identify 14 different natural and artificial sweeteners at millimolar concentrations, as well as commonly used individual-serving sweetener packets. The array has shown excellent reproducibility and long shelf life and has been optimized to work in the biological pH regime. [ABSTRACT FROM AUTHOR]

Sensitive detection of trimethylamine both in aqueous and gaseous phases has been accomplished using an inexpensive colorimetric sensor array. Distinctive color change patterns provide facile discrimination over a wide range of concentrations for trimethylamine with >99% accuracy of classification. Calculated limits of detection are well below the diagnostically significant concentration for trimethylaminuria (fish malodor syndrome). The sensor array shows good reversibility after multiple uses and is able to cleanly discriminate trimethylamine from similar amine odorants. Portable sensing of trimethylamine vapors at ppb concentrations is described using a cell phone camera or a hand-held optoelectronic nose. Application of the sensor array in detecting mouth and skin odor as a potential tool for portable diagnosis of trimethylaminuria is also illustrated. [ABSTRACT FROM AUTHOR]

Abstract: This study addresses the interplay of geometry, substrate, and dye immobilization method on colorimetric sensor array performance. Arrays of cross-responsive dyes were exposed to either ammonia or sulfur dioxide gas at their permissible exposure levels (PEL) or their immediately dangerous to life or health (IDLH) concentrations and their colorimetric responses analyzed. Two-dimensional and linear arrays in flow cells were compared for flow path uniformity. Substrate effects were explored using arrays of 36 dyes immobilized in organically modified silica sol–gel (ormosil) formulations printed on six common substrates in three classes: impermeable (glass slides and polyethylene terephthalate), cellulose based (printer paper and chromatography paper with silica gel), and porous polymer membranes (polypropylene and polyvinylidene difluoride). The effect of immobilization of dyes in an ormosil versus in a plasticizer (i.e., a viscous semi-liquid) was also compared. The linear geometry showed a more homogeneous flow path than obtained with the two-dimensional array, which contributes to higher overall response, faster response, and better reproducibility. Arrays printed on impermeable substrates showed long response times attributed to slow diffusion of the analyte through the spot, and those printed on cellulose based substrates showed high noise caused by macroscale surface texturing. Arrays printed on porous polymer substrates showed the best spot quality and reproducibility, fastest response, and lowest noise. Finally, plasticizer and ormosils proved to be comparable immobilization matrices for colorants, and the preferred choice depends on the combination of dye, immobilization method, and substrate. [Copyright &y& Elsevier]