Relationship between Wheatstone Bridge Circuit and Femtogram Particles Attached on Piezoresistive Microcantilever in Biosensor Application

Abstract

This paper describes basic calculations that are used in a piezoresistive microcantilever for the biosensor application. The working principle of the sensor is generally based on piezoresistance change due to the change of stress in the microcantilever. Such stress change is caused by the microcantilever deflection induced by the adsorption of the ultrasmall particles (virus, glucose, micro-organism, etc) on the microcantilever surface. In this work, two piezoresistors embedded in the microcantilever and two external resistors are used to build the Wheatstone bridge circuit for detecting the stress change. Basic equations in stress analysis and in Wheatstone bridge are considered in order to explain the relationship between the Wheatstone bridge and the particles attached on microcantilever surface. Calculation results show that the particles with the mass of femtogram results in piezoresistance change in the order of μΩ and the voltage output in the order of μV.