Identification and Quantitation of Aqueous Single- and Multianalyte Solutions of the Isomers Ethylbenzene, m-, p-, and o-Xylene Using a Single Specifically Tailored Sensor Coating and Estimation Theory-Based Signal Processing.

The isomer-specific detection and quantitation of m-, p-, and o-xylene and ethylbenzene, dissolved singly and as mixtures in aqueous solutions at concentrations from 100 to 1200 ppb by volume, is reported for a specifically designed polymer-plasticizer coating on a shear-horizontal surface acoustic wave (SH-SAW) device. The polystyrene-ditridecyl phthalate-blend coating was designed utilizing Hansen solubility parameters and considering the dipole moment and polarizability of the analytical targets and coating components to optimize the affinity of the sensor coating for the four chemical isomers. The two key coating sorption properties, sensitivity and response time constant, are determined by the (slightly different) dipole moments and polarizabilities of the four target analytes: as analyte dipole moment decreases, coating sensitivity increases; as analyte polarizability decreases, coating response time lengthens. Using the measured sensitivities and time constants for the targets, sensor signals were processed with exponentially weighted recursive-least-squares estimation (EW-RLSE) to identify (with near 100% accuracy) and quantify (with ± 5-7% accuracy) the isomers. This impressive performance was achieved by combining the specifically tailored, high-sensitivity coating and an SH-SAW platform (yielding a detection limit of 5 ppb for the analytes) and using the EW-RLS estimator, which estimates unknown parameters accurately even in the presence of measurement noise and for analytes with only minor differences in response. Identification of the xylene isomers is important for applications including environmental monitoring and chemical manufacturing.

Application-Specific Adaptable Coatings for Sensors: Using a Single Polymer-Plasticizer Pair to Detect Aromatic Hydrocarbons, Mixtures, and Interferents in Water with Single Sensors and Arrays.

A relatively simple design procedure is presented for new, adaptable chemical sensor coatings made from a single polymer-plasticizer pair to detect single or a mixture of chemical compounds (e.g., BTEX, the small aromatic hydrocarbon family). Affinity between coating components and target analytes, expressed through Hansen solubility parameters and relative energy difference values, describes the sensitivity of the resultant coatings to each analyte. While analyte affinity is paramount for plasticizer selection, for the aqueous-phase sensing application described here, it must be traded off with the permanence in the host polymer, i.e., resistance to leaching into the ambient aqueous phase; deleterious effects including coating creep must also be minimized. By varying the polymer:plasticizer mixing ratio, the physical and chemical properties of the resultant coatings can be tuned across a range of sensing properties, in particular the differential response magnitude and rate, for multiple analytes. Together with the measurement of multiple sensor response parameters (relative sensitivity and response time constant) for each coating, this approach allows for identification and quantification of target analytes not previously separable using commercial off-the-shelf (COTS) polymer sensor coatings. Sensing results using a five-sensor array based on five different mixing ratios of a single plasticizer polymer pair (plasticizer: ditridecyl phthalate; polymer: polystyrene) demonstrate unique identification of mixtures of BTEX analytes, including differentiation of the chemical isomers ethylbenzene and total xylene (or "xylenes"), something not previously feasible for separation-free liquid-phase sensing with commercially available polymer coatings. Ultimately, the response of a single optimized sensor coating identified and quantified the components of various mixtures, including identification of likely interferents, using a customized estimation-theory-based multivariate signal-processing technique.

Cytochemical reactions of human leprosy bacilli and mycobacteria: ultrastructural implications.

Leprosy bacilli harvested from freshly biopsied tissue from cases of lepromatous, borderline and histoid leprosy were, in conjunction with Mycobacterium lepraemurium and representative mycobacteria, examined cytochemically with and without their pyridine-extractable acid-fastness. Unlike the mycobacteria, unextracted leprosy bacilli failed to give a positive response to the periodic acid Schiff test or to take up Sudan black B, toluidine blue O, alkaline methylene blue or safranin O. Once their acid-fastness was removed with pyridine, leprosy bacilli were stained by all of the foregoing dyes except Sudan black B, under this condition they remained gram positive. While permanent loss of acid-fastness from leprosy bacilli always resulted in a loss of acid hematein-fixing material (Smith-Dietrich-Baker tests), the reverse was not true. Mild aqueous saponification, bromination, or sequential treatment with lipase and phospholipase D resulted in a loss of acid hematein-positivity but not acid-fastness. After pyridine extraction, bromination, or aqueous saponification, true mycobacteria lost neither their acid hematein-positivity nor their acid-fastness. The acid hematein-positive material and the acid-fastness of both leprosy bacilli and mycobacteria were lost after treatment with alkaline ethanol. These cytochemical findings are discussed in the light of what is known of the ultrastructure of leprosy bacilli and mycobacteria, and of the occurrence of a dl-3, 4-dihydroxyphenylalanine oxidase in leprosy bacilli but not in mycobacteria. An effort is made to explain the rather unique cytochemical properties of leprosy bacilli. Since pyridine-extractable acid-fastness (and acid hematein-positivity) serve to distinguish human leprosy bacilli from M. lepraemurium, one or the other, or both, are suggested as bases for differentiating these two organisms in animal experiments designed to show the in vivo propagation of human leprosy bacilli.