Matrix Discriminant Analysis With Application to Colorimetric Sensor Array Data

<div><p>With the rapid development of nano-technology, a “colorimetric sensor array” (CSA) that is referred to as an optical electronic nose has been developed for the identification of toxicants. Unlike traditional sensors that rely on a single chemical interaction, CSA can measure multiple chemical interactions by using chemo-responsive dyes. The color changes of the chemo-responsive dyes are recorded before and after exposure to toxicants and serve as a template for classification. The color changes are digitalized in the form of a matrix with rows representing dye effects and columns representing the spectrum of colors. Thus, matrix-classification methods are highly desirable. In this article, we develop a novel classification method, matrix discriminant analysis (MDA), which is a generalization of linear discriminant analysis (LDA) for the data in matrix form. By incorporating the intrinsic matrix-structure of the data in discriminant analysis, the proposed method can improve CSA’s sensitivity and more importantly, specificity. A penalized MDA method, PMDA, is also introduced to further incorporate sparsity structure in discriminant function. Numerical studies suggest that the proposed MDA and PMDA methods outperform LDA and other competing discriminant methods for matrix predictors. The asymptotic consistency of MDA is also established. R code and data are available online as supplementary material.</p></div

Synthesis of Poly(3,4-ethylenedioxythiophene) Microspheres by Ultrasonic Spray Polymerization (USPo)

Synthesis of Poly(3,4-ethylenedioxythiophene) Microspheres by Ultrasonic Spray Polymerization (USPo

Portable Optoelectronic Nose for Monitoring Meat Freshness

A disposable colorimetric sensor array (CSA) made from printing various chemically responsive dyes was combined with a hand-held device for on-site assessment and monitoring of the freshness of five meat products: beef, chicken, fish, pork, and shrimp. The hand-held device takes advantage of an on-board diaphragm micropump and a commercial 1D CMOS camera (CIS) which enables the real-time collection of colorimetric data. The sensor array shows excellent sensitivity to gaseous analytes, especially amines and sulfides at low ppb levels; excellent discrimination among meat volatiles in terms of meat type and storage time was demonstrated with multiple chemometric approaches including principle component analysis, hierarchical cluster analysis, and support vector machine analysis. This optoelectronic nose proves to be a promising supplement to other available techniques for meat product inspection

Ultrasonic Preparation of Porous Silica-Dye Microspheres: Sensors for Quantification of Urinary Trimethylamine <i>N</i>‑Oxide

Trimethylamine <i>N</i>-oxide (TMAO), the <i>N</i>-oxide metabolite of trimethylamine (TMA), is a key index in the determination of a wide variety of human cardiac or kidney diseases. A colorimetric sensor array comprising ultrasonically prepared silica-dye microspheres was developed for rapid, portable, and sensitive detection of urinary TMAO. To prepare the sensor array, 13 different organically modified silica (ormosil)-dye composites were synthesized from the hydrolysis/pyrolysis of ultrasonically sprayed organosiloxane precursors under optimized reaction conditions; the resulting products are uniformly sized nanoporous microspheres that are effective colorimetric sensors for various volatile analytes. The effective quantification of aqueous TMAO (which is not volatile) was based on sensing the volatile TMA produced from a simple catalytic reduction of TMAO in situ. RGB color-change patterns from digital images of the sensor array permit precise discrimination among a wide range of TMAO concentrations (10–750 μM) in simulated urine samples; both hierarchical cluster analysis and principal component analysis achieve >99% accuracy in data classification. The calculated limit of detection of urinary TMAO is ∼4 μM, which is substantially below the median level of healthy subjects (∼380 μM). The array of sensors could be simplified to only a couple of strongly responsive elements for the ease of field use, and the process could be developed as a point-of-care tool in combination with digital imaging for the early diagnosis of cardiovascular or kidney diseases from the measurement of fasting urinary level of TMAO

A Hand-Held Optoelectronic Nose for the Identification of Liquors

Successful discrimination of 14 representative liquors (including scotch, bourbon and rye whiskies, brandy, and vodka) was achieved using a 36-element colorimetric sensor array comprising multiple classes of cross-reactive, chemically responsive inks. In combination with a palm-sized image analyzer, the sensor array permits real-time identification of liquor products based on vapor analysis within 2 min. Changes in sensor spot colors before and after exposure to the vapors of the liquors that are partially oxidized as they are pumped over the sensor array provides a unique color difference pattern for each analyte. Facile identification of each liquor was demonstrated using several different multivariate analyses of the digital data library, including principal component, hierarchical cluster, and support vector machine analysis. The sensor array is also able to detect dilution (i.e., “watering”) of liquors even down to 1% addition of water. This colorimetric sensor array is a promising portable adjunct to other available techniques for quality assurance of liquors and other alcoholic beverages

Temperature Nonequilibration during Single-Bubble Sonoluminescence

Single-bubble sonoluminescence (SBSL) spectra from liquids having low vapor pressures, especially mineral acids, are exceptionally rich. During SBSL from aqueous sulfuric acid containing dissolved neon, rovibronic emission spectra reveal vibrationally hot sulfur monoxide (SO; <i>T</i>_v = 2100 K) that is also rotationally cold (<i>T</i>_r = 290 K). In addition to SO, excited neon atom emission gives an estimated temperature, for neon, of several thousand Kelvin. This nonequilibrated temperature is consistent with dynamically constrained SO formation at the liquid–vapor interface of the collapsing bubble. Formation occurs via collisions of fast neon atoms (generated within the collapsing bubble) with liquid-phase molecular species in the interfacial region, thus allowing for a mechanistic understanding of the processes leading to light emission

Thermal Explosions of Polymer-Bonded Explosives with High Time and Space Resolution

It has always been difficult to observe thermally induced explosions, because the onset is unpredictable. By use of ultrasound to induce intense, localized frictional heating at the surface of crystals embedded in a flexible polymer, we have created a new method for the initiation of microexplosions under conditions where temporal and spatially resolved observations can be made. Specifically, we report the use of ultrasound to flash-heat polymer-embedded <500 μm RDX (CH₂NNO₂)₃ and HMX (CH₂NNO₂)₄ crystals at rates >10 000 K/s. By using this extremely rapid heating on small samples, we were able to confine the explosion to narrow regions in time and space. The explosion was measured using dual thermal imagers providing temporal and spatial resolutions of 1 μs and 15 μm. Surprisingly, the explosions always occurred in <i>two stages</i>, an initial 0.1 ms stage and a subsequent 100 ms stage. The first stage of RDX explosion (2500 K lasting 140 μs) was less violent than that for HMX (4400 K lasting 70 μs), which is consistent with the general observation that HMX is regarded as a higher-performance explosive. The origin of the two-stage explosion originates from how the explosive chemistry is modulated by the mechanical behavior of the flexible polymer at the interface with the explosive crystal. The crystal explosion created a blast that produced a cavity in the surrounding polymer filled with reactive gases; subsequent ignition of the gases in that cavity caused the second-stage explosion

Thermal Explosions of Polymer-Bonded Explosives with High Time and Space Resolution

It has always been difficult to observe thermally induced explosions, because the onset is unpredictable. By use of ultrasound to induce intense, localized frictional heating at the surface of crystals embedded in a flexible polymer, we have created a new method for the initiation of microexplosions under conditions where temporal and spatially resolved observations can be made. Specifically, we report the use of ultrasound to flash-heat polymer-embedded <500 μm RDX (CH₂NNO₂)₃ and HMX (CH₂NNO₂)₄ crystals at rates >10 000 K/s. By using this extremely rapid heating on small samples, we were able to confine the explosion to narrow regions in time and space. The explosion was measured using dual thermal imagers providing temporal and spatial resolutions of 1 μs and 15 μm. Surprisingly, the explosions always occurred in <i>two stages</i>, an initial 0.1 ms stage and a subsequent 100 ms stage. The first stage of RDX explosion (2500 K lasting 140 μs) was less violent than that for HMX (4400 K lasting 70 μs), which is consistent with the general observation that HMX is regarded as a higher-performance explosive. The origin of the two-stage explosion originates from how the explosive chemistry is modulated by the mechanical behavior of the flexible polymer at the interface with the explosive crystal. The crystal explosion created a blast that produced a cavity in the surrounding polymer filled with reactive gases; subsequent ignition of the gases in that cavity caused the second-stage explosion

Rapid Quantification of Trimethylamine

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