Floating resistivity detector for microchip electrophoresis.

A newly developed conductivity detector, the floating resistivity detector (FRD), for microchip electrophoresis was introduced in this work. The detector design permits decoupling of the detection circuit from the high separation voltage without compromising separation efficiency. This greatly simplifies the integration of microchip electrophoresis systems. Its method of detection relies on platinum electrodes being dipped in two buffer-filled branched detection probe reservoirs on the microchip device. In this way, analytes passing through the detection window will not pass through and subsequently adsorb onto the electrodes, alleviating problems of electrode fouling due to analyte contamination and surface reactions. A customized microchip design was proposed and optimized stepwise for the new FRD system. Each branched detection probe was determined to be 4.50 mm long with a 0.075 mm detection window gap between them. The distance between the detection window and buffer waste reservoir was determined to be 1.50 mm. The optimized microchip design was subsequently used in the analysis of four groups of analytes - inorganic cations, amino acids, aminoglycosides antibiotics, and biomarkers. Based on the preliminary results obtained, the detection limits were in the range of 0.4-0.7 mg/L for the inorganic cations and 1.5-15 mg/L for the amino compounds.

Rapid identification of purified enteropathogenic Escherichia coli by microchip electrophoresis.

In this work, the potential of PDMS-based microchip electrophoresis in the identifications and characterizations of microorganism was evaluated. Enteropathogenic E. coli (EPEC) was selected as the model microorganism. In this study, separation parameters such as applied voltage, concentrations of buffer and buffer modifier, injection voltage, and duration of injection had been investigated and optimized. Determination of EPEC bacteria could be completed within 2 min with good reproducibility. RSDs were less than 0.5 and 5% in migration time and peak area, respectively. Separation efficiency corresponding to plate number of more than 100,000 was achieved. In order to obtain reproducible separations, sample pretreatment was found to be essential. Microchip electrophoresis with LIF detection could potentially revolutionize certain aspects of microbiology involving diagnosis, profiling of pathogens, environmental analysis, and many other areas of study.