**1. Introduction**

The era of microfluidics started in 1980s with the development of silicon etching procedures which were made for microelectronics industry. This paved way for manufacturing of first of its kind devices called Micro Electro Mechanical Systems (MEMS). In these devices mechanical microelements were integrated together on a silicon wafer. In the 1990s, researchers explored applications of these devices in the field of biology, chemistry and biomedical. They used these devices for controlling liquid's movement in micro channels which paved way for microfluidics. Laboratories on chip were developed for incorporating all the major procedures of biology, chemistry or biomedical on single platform. But, this use to come with huge cost and infrastructure for microelectronics industry. In 2000s a new era of microfluidics was started with the development of molding micro channels in polymers. This lead to decrease in cost as well as manufacturing time that caused the boom in the area of microfluidics and motivated researchers of all fields to work using them [1]. In the era of fast pacing science, microfluidic are devices to enhance pace of research and decrease the experimental cost. They run on principle of various types of taxis, majorly chemotaxis. Taxis is the

movement of particles according to some external guiding agent. This agent can be heat, oxygen, pressure, electric field or chemical, etc. Various types of taxis, their applications and microfluidics are discussed in this chapter. Microfluidic is the technology where movement of the particles is on the basis of microenvironment consisting of viscosity, surface tension and pressure. In microfluidics, micro channels are molded or etched over the silicon, glass or various polymer materials such as PolyDimethylSiloxane. These types of devices are vastly being used in all the fields of research, diagnostics and therapeutics. In microfluidics, the micro channels are formed to attain the desired result which can consist of: mixing, sorting, pumping or controlling the biochemical microenvironment. They have the advantage of decreasing the response time and experimental consumables and overall cost. They have the potential to perform large scale experimentation in small scale. Important factors to be considered for fabrication of microfluidic devices are temperature resistance, superior optical transparency of the material, high hardness, excellent electrical isolation, thermal stability, chemical inertness to many fluids, biocompatibility, and surface wettability. The performance of microfluidic device depends majorly upon etched or molded micro channel's surface properties. Therefore surface modification is an important factor to improve overall performance of microfluidic devices. Surface roughness, surface heterogeneity and solution impurity are the key parameter which affects the wettability of microfluidic device.
