**6. Conclusion**

Examples of photonic crystal waveguides and bio-sensors are presented. The main goal of the proposed chapter is to provide information about methods and approaches of biosensing systems. In the first part of the chapter we focus on the in-plane coupling of a light source by analyzing different tapered waveguide profiles able to couple W1 photonic crystals. Then we analyze different bio-sensors such as DNA sensor chip and PhC Si3N4 membrane, by discussing the irradiation and diffraction properties. In the last part we provide design criteria of a bio-compatible polymeric PhC.
