The paper describes a unique approach for a label-free biosensor designed for early-stage detection of malignant and invasive melanoma. Refractive Index variation analysis plays a vital role in the photonic crystal-based sensor design. The photonic crystal-based micro interferometer biosensor has been designed in rods in air configuration. The design comprises a hexagonal ring structure between two bus waveguides forming sensing and reference arms. The early-stage diagnosis of melanoma is dependent on the comparison of normal cells against affected cells. The diagnosis is conducted using the arms of the interferometer. The sensitivity of the biosensor is determined by the phase shift/wavelength difference between the arms of the interferometer sensor. The sensitivity of the designed sensor is 4000nm/RIU. The simulations are done using the FDTD technique. The relative shifts in frequency and wavelength are due to the refractive index deviation in the sensing arm. Quality factor is obtained at 10654.3 for the wavelength 1550 nm.