This paper presents the design and implementation of a miniature real time PCR system consisting of a disposable reactor chip, a miniature thermal cycler, and a multi-channel fiber optical fluorescence excitation/detection module. The disposable PCR chip is fabricated by using soft photolithography by PDMS (Polydimethylsiloxane) and glass. The miniature thermal cycler has a thin film heater for heating and a fan for rapid cooling. The fiber optical detection module consists of laser, filter cube, photo-detector and 1x4 fiber optical switch. It is capable of four-well real time PCR analysis. Real-time PCR detection of E. coli stx1 has been demonstrated successfully with this system.
Kinetics of passive film formation on the bare surface of scratched stainless steels SS in magnesium chloride (MgCl2) solutions were studied using the rapid scratching technique under potentiostatic conditions. An experimental device was designed to record data at the rate of 20,000 points/s, with the rotating rate of the specimen at 3,000 rpm and a scratch scar length of about 4.6 mm to 4.8 mm. A new phenomenon was observed in that two peaks were seen rather than a continuous decay in the curve of current decay on scratched SS in MgCl2 solutions. Current decayed steeply to approximately passive current within about 2.5 ms to 3 ms after the diamond knife was moved away from the specimen. Current rose again for about 2 ms to 3 ms. This phenomenon was considered to represent the processes of adsorbed layer formation on the bare surface and transformation of the adsorbed layer into a passive film. Results were affected by the recording rate of experimental data, the specimen rotating rate, and the scratch scar length. The kinetics of passive film growth were shown empirically by i(t) = I0exp(−βt) with I0 and β being constants. Passive film growth was controlled by ion conduction in a strong electric field, as defined by i = A exp(BV/x).
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