Stochastic resonance induced performance enhancement of MEMS cantilever biosensors

This paper presents an application of stochastic resonance for improving the performance of micro-electromechanical system (MEMS) cantilever biosensors operating in liquid media. The hydrodynamic influences in liquid media that consist of added mass effect, viscous damping and squeeze film damping deteriorate the Q -factor of cantilever oscillator sensors so much that their operation under fluid-immersed conditions becomes impractical. The stochastic resonance can be produced by the addition of noise in two ways: one, by direct transfer of noise energy through some nonlinear interaction process with the oscillator; and second, by making intrinsic parameters of the oscillator noisy. In this work, we are concerned with the second approach where MEMS controlled feedback oscillator is the biosensor. The cantilever motion is modeled as a damped harmonic oscillator with its natural frequency and damping coefficient parameters made noisy for generating stochastic resonance. Both the frequency and the damping noises generate stochastic resonance in the oscillator amplitude; however, the damping noise generates an additional resonance effect in the oscillator phase. The latter creates the possibility for improving Q -factor against the detrimental influences of hydrodynamic loading. This is a novel feature, which we explore in this paper for maintaining self-sustained cantilever oscillations in a liquid medium and for enhancing biosensor performance. The biosensor model takes into account the circuit loading effect and the influence of cantilever noise in hydrodynamic environment as well. The analytical relations for mass sensitivity and limit of detection have been obtained. The limit of detection is found to be inversely proportional to a Q 1 + 1 / 2 Q 2 where a and Q denote cantilever amplitude and Q -factor, respectively. That means the phase stochastic resonance produced by the addition of damping noise lowers the limit of detection by enhancing both a and Q . A prototype theoretical analysis with a Si-MEMS cantilever ( 250 × 35 × 2 μ m 3 dimensions and 10 μ m gap from boundary wall) oscillator sensor in aqueous medium shows 2 to 3 orders of magnitude enhancement in the Q -factor and 4 to 5 orders of magnitude improvement in the limit of mass detection.