Measurement of the mass and rigidity of adsorbates on a microcantilever sensor

When microcantilevers are used in the dynamic mode, the resonance shift upon material adsorption depends on the position of the adsorbate along the microcantilever. We have previously described that the adsorbate stiffness needs to be considered in addition to its mass in order to correctly interpret the resonance shift. Here we describe a method that allows obtaining the Young's modulus of the adsorbed bacteria derived from the measurement of the frequency shift when adsorbates are placed close to the clamping region. As a model system we have used E. Coli bacteria deposited on the cantilever surface by the ink-jet technique. We demonstrate that the correct information about adsorbed mass can be extracted by recording the cantilever profile and its resonance response. Also, the position and extent of adsorbates is determined by recording the microcantilever profile. We use a theoretical model based on the Euler-Bernouilli equation for a beam with both mass and flexural rigidity local increase due to the deposited material.