||Microfluidics has grown into a flourish field that holds the promise to offer better solutions for various areas such as bioanalysis and biomedical sciences with a number of advantages: small quantities of samples and reagents; high resolution and sensitivity of separation and detection; low cost; short times for analysis; and small size for portable devices. However, there is no universal fabrication method for all microfluidic applications. After two decades of fast growth in microfluidics, there are still great interests in the development of new fabrication methods of microfluidic devices for wider applications, lower cost and higher efficiency. In this work, I have solved three practical problems in the microfluidic fabrications. The first, I developed a screw-actuated system that obviates the use of compressed air to control the valve; this improvement greatly reduces the size of the whole device and thus makes it more portable and less expensive as well. The second is the establishment of a general fabrication method for hydrogel microchannels; a mixed gel with two hydrogel ingredients can not only strongly bond gel slabs together but also facilitate the bonding of the hydrogel to other materials such as glass and polymers. In the third, I invented a convenient method to fabricate microperforated membranes in photocurable materials. I have also demonstrated the application of microfluidic techniques in chemical and biological researches with construction of stepwise concentration gradient in arrays. I used three microfluidic methods that represent three different strategies to form varying concentrations: (1) dilution of the same concentrated solution with different dilution factors; (2) diffusion of molecules from a concentrated solution reservoir; (3) stepwise dilution from a concentrated solution. This research invented several microfluidic fabrication techniques and several microfluidic designs for establishment of concentration gradient. These inventions and new designs help expand the potential applications of microfluidic devices.