Optical biosensor based on arrays of waveguide microcantilevers

Abstract

Deflection of a microcantilever caused by any kind of biochemical reaction occurring on its surface can be detected with subangstrom resolution if an appropriate detection technique is exploited. This kind of transducers has become widely used in biological research since a few years ago. Usually, for the readout of the nanomechanical response of the micro beams to bio-specific interactions, a technique similar to one used in the atomic force microscopy is employed. The optical read-out method has some disadvantages, such as low degree of integration and difficulties in work with arrays of cantilevers. In the technique presented in this work the cantilever itself is an optical waveguide butt-coupled with another one. The device is fabricated as an array of 20 waveguide cantilever channels which allows for higher integration level. The analysis of the capabilities of the device, the problems associated with the design and the fabrication of the device, the choice of the material and the technology for the fabrication of very flat cantilevers have been successfully addressed. The characterisation of the device was done, showing that the resolution of the device is comparable with the one using the optical lever read-out. Results of the simulations and experimental data on the optical cantilevers coated with an absorbent material will be presented. The choice of the appropriate thickness of the absorbent material on the cantilever surface allows for acceptable losses, for single mode behaviour and adjustment of the initial displacement of the cantilever.