A study of surface stress and flexural rigidity of symmetrically and asymmetrically biofunctionalized microcantilevers

Dynamic sensing using microcantilevers has held the centre stage for a long time in biomolecular detection. In this work, we have reported a comparative study of dynamic responses of asymmetric (top or bottom surface) and symmetric (both top and bottom surfaces) modifications (biofunctionalization) of silicon nitride/oxide microcantilevers. For the first time, surface stress (in terms of surface energy/area) has been shown to govern the change in resonant frequency by studying the dynamic responses of asymmetrically and symmetrically modified microcantilevers using a conventional laser doppler vibrometer. The resonant frequency of asymmetrically modified microcantilever was found to be lower than that of symmetrically modified one by a magnitude of 0.4 kHz. Also, it was observed that the amplitude of oscillation increased from symmetrically modified to asymmetrically modified microcantilever. Consequentially, we have reported (by means of mathematical calculations and nanoindentation experiments) the increase in flexural rigidity as well as surface stress from symmetric modification to the asymmetric one. Owing to the decrease in the resonant frequencies as well as downward bending of microcantilevers, we conclude that compressive surface stress is developed after surface modifications. This work will be of immense interest to the researchers working in the field of dynamic sensing using MEMS-based sensors.