Realization of a μPCR System and Its EC Detection Circuits

Abstract

A μPCR system and its Electrochemical (EC) detection circuits are presented. The system consists of a μPCR chip packaged on a printed circuit board (PCB), peripheral signal read-out circuits and control circuits. The μPCR chip is realized with MEMStechnology contains an array of 3×4 reaction chamber. A microcontroller unit (MCU) is used in the control system to monitor the reaction procedure (PCR cycling) and handle the signal measurement. A Logarithmic Current Mode Amplifier (LGCMA) is proposed and realized as the EC signal amplification and I-V conversion. The test results shows that the obtained chip presents good Logarithmic DC characteristics within a current change from 1nA to 1μA and the corresponding output is from -4.43V to -3.52V. Thermal cycling experiment was carried to verified the control system, The results show that the variation of temperature is 0.1°C at the stable state. IntroductionPolymerase chain reaction (PCR) amplification is an essential biochemical analysis technology which is widely used in immunology, molecular biology, disease diagnosis and genetic engineering and other fields. The Micro PCR (μPCR) system has the advantage of faster response, reducing reagent consumption, lower costs and lighter weight to be portable comparing with traditional PCR system. A lot of researches on realizations of μPCR systems have been carried out and significant progress have been achieved (1, 2). A portable μPCR ideally encompass steps from target DNA amplification to PCR products detection (3), which means the integration of a small size DNA analyzer and the on-chip PCR amplification is necessary. Many μPCR chips had been proposed but the integrated DNA detection is still a bottleneck. Conventional detection methods is usually capillary electro-phoretic separation of the PCR product (along with molecular weight markers), followed by laser-excited fluorescence detection (4), but this method is very difficult to be miniaturized. EC detection method is a promising technique for DNA detection (5) and presents inherent advantages to be easily integrated with the circuits. In this paper a μPCR system with peripheral signal read-out circuits and control circuits is presented. The system was realized in board level package. A LGCMA is proposed and realized for the EC signal amplification and readout. The out-put gate voltage as a logarithmic function of the input current is obtained with the MOSFET biased in its sub-threshold region. Taped-out chip and test results of LGCMA were obtained showing a good Logarithmic DC characteristics and high sensitivity. Thermal cycling experiment was carried out using the obtained μPCR system.