Photonic crystals are the subject of intense study due to their capability to provide precise control of optical transmission characteristics through the choice of their periodic lattice parameters and the material with which they are fabricated. The sensitivity of photonic crystal band structure and defect transmission states to refractive index changes either at planar boundaries of a 2-D crystal or at individual lattice sites, make these structures potentially attractive for integrated point detection biosensor devices, given that scalable geometries and materials suitable for micro/nanofluidic addressing and co-integration with integrated source and detectors are achievable. Recent work in the literature has experimentally shown the efficacy of single defect induced intra-band gap optical transmission peak shifts for detection of refractive index changes occurring globally in either the superstrate or lattice void space. In this paper, we present results from the analysis of single and cluster defects in hole and rod geometry 2-D photonic crystal lattices to assess the efficacy of photonic crystal under selective addressing of cell clusters with micro/nano fluidic channels and under selective binding to activated crystal cell or rod surfaces by large biomolecules. Using MPB [MIT Photonic Bands] and Optiwave FDTD tools, we have analyzed the optical transmission properties of Si semiconductor photonic crystals as a function of defect cluster size and refractive index to identify design windows with viable fabrication dimensions, and measurable spectral shifts for ranges of induced refractive index change of interest. Modeling results are presented and efforts towards fabrication of prototype test structures described.