A micro polymerase chain reaction (µPCR) module for integrated and portable DNA analyses systems

This work deals with the development of a disposable miniaturized Polymerase Chain Reaction (PCR) module that will be integrated in a portable and fast DNA analysis system. The amplification device consists of a single micro-chamber reactor in which the PCR mix is confined and subjected to the thermal cycling. The chamber is completely made of PolyDimethylSiloxane (PDMS) glued to a silicon membrane, in order to exploit the silicon thermal characteristics and make the thermal cycle faster. The temperature control system is implemented by means of Platinum microheaters and thermometers are realized on the silicon substrate by Electron Beam Evaporation of Platinum and lithography-based patterning. PDMS was chosen as building material because it is biocompatible, transparent and easily moldable. The design of the device was supported by analytical and finite elements simulations in such a way to evaluate the thermal requirements. A first PCR chamber prototype was fabricated and packaged . The reaction chamber has a polygonal shape in order to facilitate the flow of liquid and to avoid residual at the edges. The chamber can hold 8µL of PCR solution and it is provided of two channels for easily loading and unloading the solution. The heater is essentially a platinum serpentine shaped in such way to make the heat flow as uniform as possible. Three platinum thermometers were added in order to control the temperature in a feedback loop. The fabrication process is divided in two separated steps: the chamber was realized using soft-lithography techniques, while the silicon membrane and the heater were micromachined in conventional MEMS technologies. A master of the reactor was obtained by spinning and patterning a thick layer of SU-8 on a Silicon substrate .Short silicone tubes were glued on the master using a drop of PDMS. PDMS, in ratio of 5:1, was then poured on the master, let polymerize for 20 minutes at 80°C and peeled away. In the meantime, a thin membrane of PDMS (20:1) was obtained and pre-polymerized 10 minutes at 80°C. The two layers were placed one on top of the other and permanently glued after the complete polymerization of the PDMS. A custom electronic board was also designed for testing the PCR thermal performances . The block diagram of the control flux is reported in Figure 3 (left). It consists of a feedback loop with a PID controller and a Pulse Width Modulator (PWM) controlling the power supplied to the heater; a thermometer and an Analog to Digital Converter (ADC) form feedback branch. The PID, MPW and the ADC were implemented directly on a micro-controller (ATmega16). Future works will be aimed at the integration of the µPCR with a detection module for realizing a portable analysis systems for point of care applications.