Study Of Microfluidic Solution Isolated Pumping And Microfluidic Sequential Flow System

The high efficiency of heat transfer and mass transfer in micro-meter scale makes microfluidics promising to advance technological progress and innovation into the Point-of-Care diagnostic and environmental monitoring, however, it is still crucial for researchers to enhance the universality, the controllability and to prevent unwanted air bubbles in the microfluidic sequential handling devices and platforms. Aiming at microfluidic sequential flow and control technologies for molecular diagnostics, this dissertation is to develop a novel microfluidic fluidic actuation method based on negative pressure, and to study an innovative universal microfluidic sequential handling system for nucleic acid assays and immunoassays to achieve controllable, multi-step, multi-sample fluidic handling in various manners. And this study is to be expected to facilitate and be beneficial to the future microfluidic products in Point-of-Care applications.Microfluidic devices that made of Polydimethylsiloxane(PDMS) are vulnerable to unwanted air bubbles, which are harmful and problematic to device functioning, especially during negative pressure-driven flow. Here we elucidate the mechanism of air bubble nucleation and growth during negative pressure-driven flow in PDMS microchannels. A theoretical model is developed to describe air bubble nucleation at different microchannel locations based on PDMS surface hydrophobicity and micro-channel geometries. To study the air bubble growth, multiphysical model is developed considering multiphase mass transfer and pressure variation, numerical simulations and experimental validation are also implemented. Correlations between the average rate of air bubble growth and key influencing parameters are studied to further understand the air bubble variation process.Based on the study of the air bubble nucleation and the variation process inside PDMS channels, here we present an elegant, negative pressure based, microfluidic Solution Isolated Pumping(μSIP) method that overcomes the drawbacks of reported large and bubble-prone microfluidic actuation systems. By taking advantage of the selectively permeable barrier, the liquid is isolated from nagetive driving pressure at the same time of facilitating the degassing of air molecules out of the fluidic channel, and the reduction of pressure in the fluidic channel pumps the liquid solution into the channel to achieve fluidic actuation. Numerical simulation and experimental analysis of μSIP are performed and compared to study the major process and the key parameters. The experimental observations also demonstrate the correlations between the design parameters and the mean flow velocity. To further demonstrate the utility of μSIP, we implemented this system in a portable and self-contained microfluidic device, with an effective integrated finger-operated pump, and accomplished continuous bubble-free loading of devices in a stand-alone manner.Placing fluidic channel and pneumatic channels in the same plane structure leads to incapability of integration of the multilayer control modules. Here we present a functional and powerful liquid handling method, and it consists of layers of thermoplastic/silicone materials to integrate 3-D structure, such as pneumatic microvalves. The fluidic layer is isolated from the pneumatic layer by a selective porous membrane, and the air in the fluidic channel is evacuated through the membrane into the negative-pressured degassing pneumatic layer during actuation to reduce the channel pressure. To enhance the efficiency of device test and design optimization, we also study the rapid, cost-efficient prototyping method for multilayer microfluidic devices, and it could transfer the chip design into physical chips within 6 hours and $10.In this dissertation, we develop a bubble-less, controllable, universal and automatic microfluidic sequential handling platform, and also the corresponding microfluidic devices with different functions. Based on the integration of pneumatic diaphragm microvalves, the developed microfluidic devices and the miniature pneumatic system could sequentially handle the fluidic samples to meet the requirement of NAs and IAs. We investigate of structure, working principle and the liquid actuation of three kinds of different microfluidic devices for NAs and IAs. We test the designed microfluidic platform, which includes the programmable miniature pneumatic system and the microfluidic chips, to achieve automatic, multi-sample, multi-reagent, multi-step sequential fluidic actuation and control.