Piezoelectric-excited millimeter-sized cantilever sensors detect density differences of a few micrograms/mL in liquid medium

We show that piezoelectric-excited millimeter-sized cantilever sensors operating in the inviscid region (Reynolds number ∼105) detect density differences of a few μg/mL. The self-sensing mechanism of the sensor provides a sensitive method and enables detection of solute concentration differences of 10 ppm. We show detection sensitivity using aqueous solutions of glycerol, sodium chloride and 1-propanol at mass fractions 0–0.2 in an isothermal (20.3 °C) measurement system. While there is good agreement with theory (∼5%) over the entire density range examined (0.9698–1.0786), considerable deviations occur at low mass fraction (∼0.001). Observation of the deviations has been possible because of the high sensitivity of the sensor used in this study and the use of continuous flow measurements. We show for the first time with continuous flow experiments that surface adsorption of solute (glycerol) contributes to the observed deviation.