Research On Pneumatically Driven Microfluidic Sampling Technology

As a promising interdisciplinary technology,microfluidics has been widely used in biochemical analysis,diagnostics,environmental science,etc.Among these applications,fluid injection is one of the key steps.It is often required to pump fluids of fixed volumes to a specific area at a specific velocity.This can be achieved using integrated micropumps.But the structure of a micropump is usually rather complex,raising the fabrication cost.Its operation also relies much on external controllers.Syringe pumps or pressure pumps can also be applied.But their volume is large,hindering the design of portable microfluidic systems.Furthermore,the fluidic capacitance effect of flexible syringes and tubes may cause large errors,especially when the volume of the fluid is small.So,microfluidic metering and injection remains a topic for further exploration.In this thesis we propose a pneumatic-driven microfluidic metering and injection system,including fluid sampling of fixed volumes and tunable fluid injection method.Main research work and relevant findings are summarized as follows:(1)A microfluidic metering and injection system is developed.A micro air pump is used to drive the fluid.Utilizing Bernoulli effect,a negative-pressure pump is also designed.Thus,using a single air pump,two different pumping pressures are realized to meet the sampling and injection requirements.External microvalves are used to simplify the system structure and to reduce the cost.(2)Utilizing hydrophobic valves and check valves,in combination with a chamber of fixed volume,accurate metering is achieved.The simple structure of hydrophobic valves helps to reduce the flow dead zone and fluid residual,and hence to increase the metering accuracy.The check valve is also optimized to improve the device reliability.Results show that,the metering error is around 1.7%.(3)A PLC controller is used to control the solenoid microvalves.The flow rate is tunable through changing the switching time and duty cycle.The dynamic characteristics of the fluid under pulsating driving pressure,and the influence of the pressure amplitude,duty cycle and fluid viscosity are investigated.