This review aims to brief about the advancement of photonic crystal based gas sensors in bio sensing field. The dynamic properties of photonic crystal sensors viz its sensitivity, stability, quality factor and its miniature size attributes to the development of high sensitive photonic crystal based optical gas sensors. Photonic crystals have periodic structures with different dielectric constant along the structure. Defects are introduced in the structure of the sensor which helps in confining the light in the structure. The refractive index variation in presence of an analyte shifts the resonance of the structure. Thus the shift in the resonant peak with an proportional change in the refractive index makes it a highly sensitive refractive index gas sensor. These sensors have shown great potential in detecting a wide range of analytes including gases, liquids, and biomolecules. In particular, they have been extensively used in wide range of applications in industry, healthcare, and research. This paper discusses the recent progress in design and analysis of various PhC based biosensors and hence shows the possibility of devising a highly sensitive, stable, label-free and non-invasive homogenous sensor allowing real-time monitoring in various environments.