Faculty Bibliography

The development of a novel chip-based multianalyte detection system with a cardiac theme is reported. This work follows the initial reports of "electronic taste chips" whereby multiple solution-phase analytes such as acids, bases, metal cations, and biological cofactors were detected and quantitated. The newly fashioned "cardiac chip" exploits a geometry that allows for isolation and entrapment of single polymeric spheres in micromachined pits while providing to each bead the rapid introduction of a series of reagents/washes through microfluidic structures. The combination of these miniaturized components fosters the completion of complex assays with short analysis times using small sample volumes. Optical signals derived from single beads are used to complete immunological tests that yield outstanding assay characteristics. The power and utility of this new methodology is demonstrated here for the simultaneous detection of the cardiac risk factors, C-reactive protein and interleukin-6, in human serum samples. This demonstration represents the first important step toward the development of a useful cardiac chip that targets numerous risk factors concurrently and one that can be customized readily for specific clinical settings.

Specific attributes of the taste, aroma and texture of a food product or beverages drives consumer preference and purchase intent. Generally, in product development stages, products are tested in sensory panels to determine which variant of a chosen set is the ideal candidate for further consumer testing leading to commercialization. However, sensory tasting panels are fatiguing and require commitment on the part of panelists to attend and be consistent in their evaluation of randomly presented samples. In the absence of a willing, precise and trained human taste panel, as well as the need for a high through-put screening tool capable of real time assessment of product quality, the need for in vitro taste sensors correlated to human sensory perception is growing. In the industrial and academic limelight, one such technology is affectionately called an electronic tongue.

An array for the simultaneous detection of multiple analytes in a solution has been developed. Single analyte receptors on resin beads in conjunction with fluorescent and colorimetric signaling strategies are the basis of the sensing ensemble. The pattern created is specific for each particular set of stimuli, allowing for analyte detection, analogous to the mammalian tongue.

We report the development of a sensor for rapidly and simultaneously measuring multiple sugars in aqueous samples. In this strategy, enzyme-based assays are localized within an array of individually addressable sites on a micromachined silicon chip. Microspheres derivatized with monosaccharide-specific dehydrogenases are distributed to pyramidal cavities anisotropically etched in a wafer of silicon (100) and are exposed to sample solution that is forced through the cavities by a liquid chromatography pumping system. Production of fluorescent reporter molecules is monitored under stopped-flow conditions when localized dehydrogenase enzyme systems are exposed to their target sugars. We demonstrate the capability of this analysis strategy to quantify beta-D-glucose and beta-D-galactose at low micromolar to millimolar levels, with no detectable cross-talk between assay sites. Analysis is achieved either through fluorescence detection of an initial dehydrogenase product (NADH, NADPH) or by production of a secondary fluorescent product created by hydride transfer from the reduced nicotinamide cofactor to a fluorogenic reagent. The array format of this sensor provides capabilities for redundant analysis of sugars and for monitoring levels of other solution components known to affect the activity of enzymes. The use of this strategy to normalize raw fluorescence signals is demonstrated by the determination of glucose and pH on a single chip. Alternatively, uncertainties in the activity of an immobilized enzyme can be accounted for using standard additions, an approach used here in the determination of serum glucose.