A photonic crystal waveguide biosensor in the visible is presented for biosensing. The sensor is applied to Refractive Index (RI) measurements. The sensitivity at different wavelength is presented for both air holes and air core configurations of photonic crystal waveguide (PCW) made of TiO2. It is shown that by using Atomic Layer Deposition (ALD) the expected sensitivity of the air core configuration outperforms the previously reported results.