Fabrication Of PDMS Microfluidic Chips And The Application In PH Sensing

The measurement of pH is closely related to the field of modern industry, agriculture, biomedical engineering, and environmental science, especially about the treatment of industrial wastewater. However, most of pH sensors working with sampling method, they can’t make respond to the pH changes of industrial wastewater timely and make it difficult to control the damage caused by the pollution at the first time. Microfluidic system is based on a network of micro-channels. Fluid is controllable throughout the system. So microfluidic system can meet the need of monitoring the fluid of the pipe in real-time. Polydimethylsiloxane (PDMS) becomes a common polymer material for fabricating microfluidic chips due to its qualities as low cost and good transparency. Under the backgrounds, a pH-sensing PDMS microfluidic chip system which can monitor the pH of wastewater in real-time is set up. The main contents of this thesis include followings:A pH-sensing substrate is fabricated. Entrapment method is applied to immobilize the pH indicator on the surface of PDMS substrate. Methyl red sodium salt is selected as indicator, because it can be dissolved in both organic solvent and water. The pH sensing film is attached on the PDMS substrate by spin coating. Optimal proportion between polymer and indicator solution to get good pH-sensing performance is determined.A pH-sensing microfluidic chip is fabricated by bonding cover and substrate. A cover with a channel is made by casting PDMS onto a male mold, and the size of the channel is 25mm×5mm×0.9mm. The surface structure of the pH-sensing substrate is designed to two regions, a pH-sensing zone and a detection zone. Their sizes are 15mmx5mm and 10mmx5mm respectively. Oxygen plasma can change surface hydrophobicity of PDMS, and it is used to help bonding cover and substrate.The pH-sensing microfluidic system is set up and tested. A light-electric-conversion circuit is established. Mixture solutions of different buffers and pH indicator are used to test the circuit. The circuit alarms when the solution pH is higher than the pre-set threshold, and the set pH threshold is adjustable. Finally, the pH-sensing microfluidic system, including a pH-sensing microfluidic chip, an injection pump, and an alarm circuit, is successfully tested.