Preliminary testing of a prototype instrument employing an integrated array of six polymer-coated flexural plate wave (FPW) sensors and an adsorbent preconcentrator is described. Responses to thermally desorbed samples of individual organic solvent vapors and binary and ternary vapor mixtures are linear with concentration, and mixture responses are equivalent to the sums of the responses of the component vapors, which co-elute from the preconcentrator in most cases. Limits of detection as low as 0.3 ppm are achieved from a 60-s (34 cm3) air sample and peak widths at half-maximum range from 1 to 4 s. Tests at different flow rates suggest that the kinetics of vapor sorption in the sensor coating films may limit responses at higher flow rates, however, low data acquisition rates may also be contributory. Assessments of array performance using independent test data and Monte Carlo simulations with pattern recognition indicate that individual vapors and certain binary and ternary mixtures can be recognized/discriminated with very low error. More complex mixtures, and those containing homologous vapors, are problematic. This is the first report demonstrating multi-vapor analysis with an integrated FPW sensor array.

A device was developed that uses microfabricated fluidic channels, heaters, temperature sensors, and fluorescence detectors to analyze nanoliter-size DNA samples. The device is capable of measuring aqueous reagent and DNA-containing solutions, mixing the solutions together, amplifying or digesting the DNA to form discrete products, and separating and detecting those products. No external lenses, heaters, or mechanical pumps are necessary for complete sample processing and analysis. Because all of the components are made using conventional photolithographic production techniques, they operate as a single closed system. The components have the potential for assembly into complex, low-power, integrated analysis systems at low unit cost. The availability of portable, reliable instruments may facilitate the use of DNA analysis in applications such as rapid medical diagnostics and point-of-use agricultural testing.

Water-in-oil microdroplets in microfluidics are well-defined individual picoliter reaction compartments and, as such, have great potential for quantitative high-throughput biological screening. This, however, depends upon contents of the droplets not leaking out into the oil phase. To assess the mechanism of possible leaking, the retention of various fluorescein derivatives from droplets formed in mineral oil and stored for hours in a reservoir on chip was studied. Leaking into the oil phase was observed and was shown to be dependent on the nature of the compounds and on the concentration of the silicone-based polymeric surfactant Abil EM 90 used. In experiments in which droplets filled with fluorescein were mixed with droplets filled with only buffer, the rate of efflux from filled droplets to empty droplets was dependent on the number of neighboring droplets of different composition. Buffer droplets with five fluorescein-containing neighbors took up the fluorophore 4.5 times faster than buffer droplets without fluorescein neighbors. The addition of bovine serum albumin (BSA) substantially reduced leaking. A formulation with 5% BSA reduces leaking of the fluorophore from 45% to 3%. Inclusion of BSA enabled experiments to be carried out over periods up to 18 h, without substantial leaking (<5%). We demonstrate the utility of this additive by following the enzymatic activity of alkaline phosphatase expressed by Escherichia coli cells. The ability to reliably compartmentalize genotype (cell) and phenotype (reaction product) is the basis for using microdroplets in directed evolution studies, and the approaches described herein provide a test system for assessing emulsion formulations for such purposes. The use of droplets as individual reactors, formed and manipulated in microfluidic devices, offers a potentially powerful format for performing large numbers of chemical or biochemical experiments on a small scale (typically in pico-to nanoliter volumes) in parallel. 1-3 Such droplets have been used to measure fast enzyme kinetics, 4-8 for cell-based assays,