Sensors and Actuators B 105 (2005) 251–258 A microchip-based PCR device using flexible printed circuit technology Keyue Shen a,b , Xiaofang Chen a,b , Min Guo b , Jing Cheng a,b,c,∗ a Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing 100084, China b National Engineering Research Center for Beijing Biochip Technology, 18 Life Science Parkway, Changping District, Beijing 102206, China c State Key Laboratory of Biomembrane and Membrane Biotechnology, Tsinghua University, Beijing 100084, China Received 13 February 2004; received in revised form 26 May 2004; accepted 27 May 2004 Available online 22 July 2004 Abstract Rapid heat transfer is crucial for an efficient polymerase chain reaction (PCR), and this makes temperature control one of the most essential features in a micro-PCR system, which always includes a heater and a sensor composing a closed-loop. Yet, the fabrication of the heater and the sensor often prevented micro-PCR systems from achieving both cost-effectiveness and fabrication-easiness. For most of the early researches micromachining techniques were used to allow sensors and heaters be integrated on a silicon or glass chip. However, the cost prevented them from wide applications. The work described in this paper is part of our effort to solve the cost/fabrication dilemma. An innovative digital temperature control system was developed by introducing a heater/sensor switching procedure. Only one temperature controlling element fabricated by flexible printed circuit technology was utilized in the constructed PCR device with minimum fabrication steps. The glass chip-based device was made from low cost materials and assembled with adhesive bonding. Through seemingly simple steps, we obtained both disposability and portability at the same time. Temperature stability within ±0.3 ◦ C and a transitional rate of 8 ◦ C/s during heating/cooling was achieved. A 244 bp DNA fragment of hepatitis C virus was successfully amplified in our device by a three-stage thermal cycling process. Further improvement was assisted by finite element analysis, and demonstrated by experiment. © 2004 Elsevier B.V. All rights reserved. Keywords: Micro-PCR; Thermal component; Flexible printed circuit (FPC); Finite element analysis (FEA) 1. Introduction Polymerase chain reaction (PCR) has been playing a cen- tral role in nucleic acid analyses since 1983. It is a temper- ature controlled and enzyme-mediated amplification tech- nique for nucleic acid molecules, usually consisting of pe- riodical repetition of three reaction steps: a denaturing step at 92–96 ◦ C, an annealing step at 37–65 ◦ C (determined by the inherent nucleic acid sequences) and an extending step at ∼72 ◦ C. The basic requirement for an efficient amplification is rapid heat transfer [1]. Consequently, it is desirable to have a device with a low thermal capacity and high heat con- ductivity. For most of the traditional PCR instruments, the heating and cooling rates were slow because of their rela- tive large thermal components. Miniaturization of conven- tional PCR devices could bring in great saving in space, ∗ Corresponding author. Tel.: +86-10-62772239; fax: +86-10-80726898. E-mail address: jcheng@tsinghua.edu.cn (J. Cheng). time and reagents, and accelerate the amplification process by increasing the surface to volume ratio [2]. In general, a micro-PCR system should be composed of two functional parts: a fabricated three-dimensional structure and a temperature control system. Early development of silicon-based micro-PCR devices were facilitated by the micro-fabrication technology [3–5]. Silicon was preferred because of its high thermal conduc- tivity and controllable etching properties. This material is not transparent, and untreated silicon may cause inhibition to PCR [6]. Glass has the advantage of being electrically nonconductive and optically transparent. Yet, it is not as amenable as silicon in micromachining. Moreover, fabrica- tion of silicon/glass structures usually involves processes such as photolithography, wet etching, electrochemical etch- ing and anodic bonding. The high costs of these processes cannot accommodate the disposability required by PCR re- actions to avoid cross-contamination. Recently, plastic ma- terials are more popular for its ease of use, low cost and disposability, and there are many established techniques for building complex structures. For example, polycarbonate 0925-4005/$ – see front matter. © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2004.05.069