and radius between different particles, these particles can be separated by viscosity and velocity. In this way, the sedimentation of different particles can be achieved. Materials Many structures can be formed using the most common, rapid prototyping technology, soft lithography with polydimethylsiloxane(PDMS). PDMS is an inexpensive, clear elastomeric polymer with rubbery mechanical properties at room temperature. In the laboratory, PDMS is mixed in small batches, poured onto moulds, for example, poly(methyl methacrylate)(PMMA), with microscale features, and cured at moderate temperatures for minutes to hours. Open PDMS channels are closed by adhering the channel bearing component to a glass slide or a second, flat piece of PDMS. Inlets and outlets can be formed easily using punch tools. Although many surface modifications are not permanent on PDMS due to its relatively high chain mobility compared with polymers, PDMS still remains relevant as a material for microfluidic applications. Thermoplastics are also coming into use. The use of engineering thermoplastics has many advantages, although most of these advantages have not yet been realized. There are a few commodity plastics that have emerged as suitable for medical microfluidic applications. These include poly(methyl methacrylate)(PMMA), polystyrene, polycarbonate, and a variety of cyclic polyolefin materials. PMMA has good optical properties for fluorescence, and UV detection modes are relatively easy to seal to themselves. These are available in grades suitable for both injection and compression molding. Polystyrene is a material known for assay development. Polycarbonates have a high glass transition temperature but poor optical properties for fluorescent detection. The cyclic polyolefins appear to have the best combination of optical and mechanical properties. Detection Signal sending Sample preparation Before the molecules react with the reagents, they should be prepared for the reactions. The most typical is separation by centrifugal force. In the case of blood, for example, the sedimentation of blood cells from plasma can be achieved by rotating the biodisk for some time. After separation, all molecular diagnostic assays require a step of cell/viral lysis in order to release genomic and proteomic material for downstream processing. Typical lysis methods include chemical and physical method. The chemical lysis method, which is the simplest way, uses chemical detergents or enzymes to break down membranes. The physical lysis can be achieved by using bead beating system on a disk. Lysis occurs due to collisions and shearing between the beads and the cells and through friction shearing along the lysis chamber walls. ELISA/FIA