A grating-based optical readout method for microcantilever biosensor

For measuring the deflections of the microcantilever biosensor, a reflective grating microcantilevers based on SOI were designed and fabricated, a high precision optical readout approach based on diffraction spectrum balancing feedback control was presented. The diffraction spectrum image was collected by a 12-bit digital area array monochrome CCD. According to the sum gray value of the image which subtracted each other at the balancing position and bending position to control a high precision motorized rotation stage revolve make the sum gray value remained in the balancing position always, then the motorized rotation stage revolving angle is just the cantilever bend angle. The resolution of motorized rotation stage is 35 × 10−6 deg, the system practical measurement resolution is 1 × 10−4 deg, that is to say, for a length of 250 μm microcantilever, the tip measure resolution is up to 0.043 nm. Measurement results clearly demonstrate that this reflective grating microcantilever biosensor and this read out method have a great potential for biological and chemical applications.