Studies On Micro-fluid Manipulating Methods Based On PDMS Pneumatic Valves And Their Applications

Micro-fluid driving and mixing techniques are common fluid manipulating methods in microfluidic systems. The micro-fluid driving methods are responsible for fluid transportation and distribution, which are the premise and basis of micro-fluid manipulating. On the other hand, fluid mixing is indispensible in all chemical, biochemical and molecular biological reactions. Considering the laminar nature of fluid in the microfluidic system, fast and efficient mixing becomes vitally important. The characteristic features of polydimethylsiloxane (PDMS), e.g., ease of molding, fabricating and bonding, transparency as well as flexibility, make it a popular material for pneumatically actuated valves/pumps in microfluidic systems. In this paper, the efficient methods for micro fluid mixing and driving based on PDMS pneumatic valves were studied. The experimental results of the fluid mixing/driving and their applications in chemical and molecular biological reactions adequately demonstrated the superiority of these pneumatic fluid manipulating methods,A pneumatic micro-mixing device consisting of two pneumatic chambers and an underneath DNA microarray chamber was built up. The fluid in the array chamber was pneumatically pumped alternately by the two pneumatic chambers. The chaotic oscillatory flow caused by the pumping greatly intensified the fluidic mixing. A homogeneous distribution of the tracer dye solution in the microarray chamber was observed after2s mixing at a pumping frequency of24Hz with a100-μm thick diaphragm and a gas pressure of0.08MPa. Microarray DNA hybridization was substantially accelerated using this device, and the fluorescence intensity showed a plateau after oscillating30s at room temperature. The corresponding signal level of the dynamic hybridization was11.5-fold higher than that of the static hybridization performed at42℃. The nonspecific adsorption of the targets to the sample array was weakened after dynamic hybridization and a117-fold signal-to-noise ratio was achieved.A novel fluid mixing strategy integrated in microfluid channel based on pneumatic ejection was developed. The pneumatic micro-mixing device consists of two pneumatic chambers and an underneath fluid channel with an S-shaped fluid mixing structure and two flow barriers. The fluid in the mixing chamber was instantaneously extruded by pneumatic pumping and then impacted against the barriers downstream the fluid mixing chamber. The chaotic flow caused by the pneumatic ejection greatly intensified the fluidic mixing. When using a gas pressure of0.26MPa and a100μm-thick PDMS diaphragm, the fast mixing of the fluids with flow rates ranging from1-650μL/min were achieved with a pumping frequency of50Hz. Fast synthesis of CdS quantum particles was substantially achieved using this device, smaller particles were obtained and the size distribution was greatly improved compared with conventional method.A novel extrusion fluid driving protocol was developed based on microfabricated PDMS pneumatic valves. High efficiency liquid transfer was performed by using entirely overlapping control channels and fluid channels. A0.5-s time suffices the transfer of9μL sample solution between two chambers with a nitrogen pressure of0.07MPa. The driving method was used in a microfluidic continuous flow polymerase chain reaction (PCR) system, and rapid cycling of the PCR mixture in a closed loop was achieved. The amplification of DNA fragments were demonstrated via both three-stage and two-stage PCR thermal cycling protocols on the microchips. Amplifications of144-bp and200-bp DNA fragments were achieved within24min using three-stage thermal cycling, and130-bp DNA fragments within12min using two-stage thermal cycling.