The present disclosure provides methods and mechanisms for measuring small masses attached to a substrate within a microcantilever. Specifically, the disclosure describes the measurement of small particles accumulated at a substrate that cannot be flowed through a microchannel within a microcantilever. A resonance measurement is acquired at a first time. A pair resonance measurements is then acquired at a second point in time—one with the test mass at a first position off or along the microcantilever, the second with the test mass at a second position along the microcantilever. Comparing the resonance frequencies determined for the two test mass positions allows for disambiguation of changes in the mass of the particles from changes in the resonant behavior of the microcantilever itself.