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Label-free biosensor based on the dynamic distributed feedback (DFB) laser emission is proposed. The sensitivity of the sensor is substantially realized by the refractive index of the cladding layer that influences the effective refractive index (neff) of the whole waveguide structure. The designed multilayer structure consists of the substrate (n=1.51), the low refractive index mesoporous silica film (n=1.1~1.3), the dye-doped gain layer (n=1.58) and the high refractive index TiO2 (n=2.1) thin film. We used the finite difference time domain (FDTD) algorithm to simulate the influence of the mesoporous silica film and the TiO2 layer to the neff of the fundamental transverse electric (TE0) mode and the sensitivity in the DFB structure. It was found that the increase of refractive index of the mesoporous silica and the thickness of TiO2 layer can slightly increase the neff of the structure. And the sensitivity of the sensor can be enhanced not only by the introduction of mesoporous silica, but also by a thicker TiO2 layer.