Chiral sensing using a complementary metal-oxide semiconductor-integrated three-transducer microsensor system.

Different chiral cyclodextrin derivatives were dissolved in a polysiloxane matrix and have been used as sensitive coatings on a three-transducer microsystem including a calorimetric, a mass-sensitive, and a capacitive chemical sensor. Upon exposure to chiral analytes, such as methyl lactate and methyl-2-chloropropionate, all three transducers showed distinct chiral discrimination of these analytes. The signals were found to constitute a convolution of sorption thermodynamics and transducer-specific contributions, which included, in the case of the capacitive sensor, molecular orientation effects so that even opposite-sign signals for the two enantiomers resulted. The sensor response curves of all three transducers could be explained and fitted by applying a model that essentially implies the superposition of a Langmuir isotherm representing specific interactions, predominant at low concentrations, and a Henry isotherm for nonspecific physisorption. The results disclosed here show that, on the one hand, sensor techniques can be used to reveal details of enantioselective analyte-receptor or analyte-matrix interactions and that, on the other hand, sensors may provide an even more pronounced chiral discrimination ("discrimination enhancement") with respect to sorption-thermodynamics-determined gas chromatography as a consequence of the transducer-specific signal contributions.

Direct determination of the enantiomeric purity or enantiomeric composition of methylpropionates using a single capacitive microsensor.

Capacitive enantioselective sensors have been demonstrated to provide antipodal signals upon dosage of, e.g., the enantiomers of methyl lactate or methyl-2-chloropropionate. In a next step, these sensors have been used to not only qualitatively determine the nature of the respective enantiomer or to quantitatively measure its concentration upon dosage in the pure form but to also assess the enantiomeric composition of mixtures by using only a single capacitive-type sensor. The enantioselective coating material consisted of a modified gamma-cyclodextrin. It was shown that the absorption and desorption kinetics of the two enantiomers of, e.g., the methyl-2-chloropropionate, are sufficiently different and produce sensor signal features that enable an accurate determination of the enantiomeric purity and composition of the chiral analyte or mixture under investigation. The method even allows for detecting small impurities in commercially available samples labeled as 99% enantiomerically pure. Moreover, the results disclosed here show that sensor techniques can be used to reveal details of enantioselective analyte-receptor and analyte-matrix interactions.

Evaluation of multitransducer arrays for the determination of organic vapor mixtures.

A study of vapor recognition and quantification by polymer-coated multitransducer (MT) arrays is described. The primary data set consists of experimentally derived sensitivities for 11 organic vapors obtained from 15 microsensors comprising five cantilever, capacitor, and calorimeter devices coated with five different sorptive-polymer films. These are used in Monte Carlo simulations coupled with principal component regression models to assess expected performance. Recognition rates for individual vapors and for vapor mixtures of up to four components are estimated for single-transducer (ST) arrays of up to five sensors and MT arrays of up to 15 sensors. Recognition rates are not significantly improved by including more than five sensors in an MT array for any specific analysis, regardless of difficulty. Optimal MT arrays consistently outperform optimal ST arrays of similar size, and with judiciously selected 5-sensor MT arrays, one-third of all possible ternary vapor mixtures are reliably discriminated from their individual components and binary component mixtures, whereas none are reliably determined with any of the ST arrays. Quaternary mixtures could not be analyzed effectively with any of the arrays. A "universal" MT array consisting of eight sensors is defined, which provides the best possible performance for all analytical scenarios. Accurate quantification is predicted for correctly identified vapors.

Detection and discrimination capabilities of a multitransducer single-chip gas sensor system.

The performance of a single-chip, three-transducer, complementary metal oxide semiconductor gas sensor microsystem has been thoroughly evaluated. The monolithic gas sensor system includes three polymer-coated transducers, a mass-sensitive cantilever, a thermoelectric calorimetric sensor, and an interdigitated capacitive sensor that are integrated along with all electronic circuits needed to operate these sensors. The system additionally includes a temperature sensor and a serial interface unit so that it can be directly connected to, for example, a microcontroller. Several multitransducer chips have been coated with various partially selective polymers and then have been exposed to different volatile organic compounds. The sensitivities of the three different polymer-coated transducers to defined sets of gaseous analytes have been determined. The obtained sensitivity values have then been normalized with regard to the partition coefficients of the respective analyte/polymer combination to reveal the transducer-specific effects. The results of this investigation show that the three different transducers respond to fundamentally different molecular properties, such as the analyte molecular mass (mass-sensitive), its dielectric coefficient (capacitive), and its sorption heat (calorimetric) so that correlations between the determined sensitivity values and the different molecular properties of the absorbed analytes could be established. The information as provided by the system, hence, represents a body of orthogonal data that can serve as input to appropriate signal processing and pattern recognition techniques to address issues such as the quantification of analytes in mixtures.

A microfabricated array bioreactor for perfused 3D liver culture.

We describe the design, fabrication, and performance of a bioreactor that enables both morphogenesis of 3D tissue structures under continuous perfusion and repeated in situ observation by light microscopy. Three-dimensional scaffolds were created by deep reactive ion etching of silicon wafers to create an array of channels (through-holes) with cell-adhesive walls. Scaffolds were combined with a cell-retaining filter and support in a reactor housing designed to deliver a continuous perfusate across the top of the array and through the 3D tissue mass in each channel. Reactor dimensions were constructed so that perfusate flow rates meet estimated values of cellular oxygen demands while providing fluid shear stress at or below a physiological range (<2 dyne cm(2)), as determined by comparison of numerical models of reactor fluid flow patterns to literature values of physiological shear stresses. We studied the behavior of primary rat hepatocytes seeded into the reactors and cultured for up to 2 weeks, and found that cells seeded into the channels rearranged extensively to form tissue like structures and remained viable throughout the culture period. We further observed that preaggregation of the cells into spheroidal structures prior to seeding improved the morphogenesis of tissue structure and maintenance of viability. We also demonstrate repeated in situ imaging of tissue structure and function using two-photon microscopy.