Design and fabrication of microfluidic/microelectronic devices from nano particle based composites

In this thesis, two kinds of nanoparticle functional composite Giant Electrorheological(GER) fluid and polydimethylsiloxane (PDMS) conductive composites and their applications in micro scales are studied. GER fluid is synthesized with ~50 nm polarizable solid particles and non-polarizable oil, whose apparent viscosity is continuously variable through applications of an electric field. We have successfully applied ER fluid as actuations in microfluidic chips. With soft lithography techniques, we developed various micro functional chips based on PDMS, including micro flexible platform, micro active mixer and micro pump, all of which have desirable performances. The PDMS conducting composites are synthesized by mixing nano to sub micro-sized conductive particles (silver/carbon black) with PDMS gel. Such composite materials exhibit good electrical conductivity and mechanical reliability, as well as desirable thermal characteristics. By employing this type of composite, we have developed some realistic micro-structural devices and explored their potential applications, including flexible bio-electrodes, micro-heaters and flexible displays, micro temperature indicators, etc. With these two composites and corresponding results, we succeeded in realizing a highly integrated microfluidic chip with the function of DNA amplification. The system has the advantages of small size with a high degree of integration, high PCR efficiency, digital control and simple fabrication at low cost and shows promise for a broad range of applications in chemical synthesis and biological sensing/analysis