The analytical performance of a porous silicon Bloch surface wave biosensors as protease biosensor

We investigate the analytical performance of label free porous silicon Bloch surface wave (BSW) devices as protease sensors. Protease detection is based on the digestion of gelatin, which was covalently immobilized onto the surface modified PSi structure. Exposure to the protease enzyme, subtilisin initiates catalytic degradation of the gelatin gel network. The degradation of this network which is present in the top layer of the sensor, causes a blue shift in the spectral position of the Bloch surface mode. The magnitude of the resonance shift is directly proportional to the concentration of subtilisin and the digestion time. The lowest concentration of subtilisin detected was 370 pM. Secondary spectral features, such as band-edge modes, are relatively insensitive to refractive index changes in the superficial layers and thus can be utilised as an internal reference to exclude any nonspecific adsorption and bonding that may occur through the bulk of the film. The advantages of the system here include fast diffusion of digested product and self-referencing capability.