Miniaturized measurement system for ammonia in air

Point of care monitoring of hemodialysis patients with a breath ammonia measurement device based on printed polyaniline nanoparticle sensors

A device for measuring human breath ammonia was developed based on a single use, disposable, inkjet printed ammonia sensor fabricated using polyaniline nanoparticles. The device was optimized for sampling ammonia in human breath samples by addressing issues such as variations in breath sample volume, flow rate, sources of oral ammonia, temperature and humidity. The resulting system was capable of measuring ammonia in breath from 40 to 2993 ppbv (r(2 )= 0.99, n = 3) as correlated with photoacoustic laser spectroscopy and correlation in normal human breath samples yielded a slope of 0.93 and a Pearson correlation coefficient of 0.9705 (p < 0.05, n = 11). Measurement of ammonia in the breath of patients with end-stage kidney disease demonstrated its significant reduction following dialysis, while also correlating well with blood urea nitrogen (BUN) (r = 0.61, p < 0.01, n = 96). Excellent intraindividual correlations were demonstrated between breath ammonia and BUN (0.86 to 0.96), which demonstrates the possibility of using low cost point of care breath ammonia systems as a noninvasive means of monitoring kidney dysfunction and treatment.

A microfluidic chip for electrochemical conversions in drug metabolism studies

We have designed a microfluidic microreactor chip for electrochemical conversion of analytes, containing a palladium reference electrode and platinum working and counter electrodes. The counter electrode is placed in a separate side-channel on chip to prevent unwanted side-products appearing in the measured spectrograms. Using this chip, cyclic voltammograms are measured in volumes of 9.6 nL. Furthermore the conversion efficiency of ferricyanide is characterized using UV/vis-spectroscopy. We have obtained an on-line conversion of 97% using a flow rate of 1 microL/min. We have used the microreactor chip to study the electrochemical metabolism pathway of amodiaquine using electrochemistry (EC)-liquid chromatography (LC)-mass spectrometry (MS). We have compared our results with measurements obtained with commercially available electrochemical flow-through cells. Using our chip it was possible to obtain similar results. Therefore, we have fabricated an electrochemical cell on-chip which is used successfully in EC-UV/vis and EC-LC-MS experiments.

Integrated membrane filters for minimizing hydrodynamic flow and filtering in microfluidic devices

Microfluidic devices have gained significant scientific interest due to the potential to develop portable, inexpensive analytical tools capable of quick analyses with low sample consumption. These qualities make microfluidic devices attractive for point-of-use measurements where traditional techniques have limited functionality. Many samples of interest in biological and environmental analysis, however, contain insoluble particles that can block microchannels, and manual filtration prior to analysis is not desirable for point-of-use applications. Similarly, some situations involve limited control of the sample volume, potentially causing unwanted hydrodynamic flow due to differential fluid heads. Here, we present the successful inclusion of track-etched polycarbonate membrane filters into the reservoirs of poly(dimethylsiloxane) capillary electrophoresis microchips. The membranes were shown to filter insoluble particles with selectivity based on the membrane pore diameter. Electrophoretic separations with membrane-containing microchips were performed on cations, anions, and amino acids and monitored using conductivity and fluorescence detection. The dependence of peak areas on head pressure in gated injection was shown to be reduced by up to 92%. Results indicate that separation performance is not hindered by the addition of membranes. Incorporating membranes into the reservoirs of microfluidic devices will allow for improved analysis of complex solutions and samples with poorly controlled volume.

Micro gas analysis system for measurement of atmospheric hydrogen sulfide and sulfur dioxide

A honeycomb structure microchannel scrubber was developed to achieve efficient and stable gas collection. A thin porous membrane was pasted on a microchannel by the adhesive force of a fresh polydimethylsiloxane surface. The microchannel scrubber achieved much more efficient gas collection than conventional impingers and diffusion scrubbers. Two sets of the microchannel scrubbers and detectors were integrated in a 10 cm x 9 cm plastic board to create a micro gas analysis system (microGAS) for simultaneous measurements of H2S and SO2. The whole system including a battery was incorporated in a carrying case 34 cm W x 16 cm D x 17 cm H for use in the field. Liquid flows at 30 microl min(-1) were obtained by bimetal micropumps. The estimated detection limits were 0.1 ppbv for H2S and 1 ppbv for SO2. The system was demonstrated for real atmospheric gas analysis, and the results agreed well with data concurrently obtained by ion chromatography coupled with a cylindrical diffusion scrubber. The system we developed allowed automated continuous analyses in the field and achieved a much higher time resolution compared to those by ion chromatographic analysis.