Biological or biochemical sensing and quantification are of critical importance for medical, biological, chemical, and biotechnological applications. Biosensor represents a device that can detect and measure a specific biological organism in a biological or biochemical process with a large variety of samples including body fluids, food samples, cell cultures, and environmental samples. Microfluidics is the science and technology of handling and analyzing fluids in the micrometer scale. Because of scaling, shrinking existing large devices and expecting them to function well at the microscale is often counterproductive. It is critical for researchers who design new devices to understand microfluidic physics and physical phenomena including laminar flow, diffusion, fluidic resistance, surface area to volume ratio, and surface tension that dominate at the microscale. Polydimethylsiloxane (PDMS) has been one of the most actively developed polymers for microfluidics. Fabrication of systems and channels in PDMS is particularly straightforward since it can be cast against a suitable mold with sub-0.1-µm fidelity.