Piezoelectric cantilever sensors with asymmetric anchor exhibit picogram sensitivity in liquids

We show for the first time that self-exciting and self-sensing piezoelectric cantilevers consisting only of lead zirconate titanate (PZT) measure resonance only if they are asymmetrically anchored. Symmetric-anchoring did not give rise to electrically measurable bending resonant modes in the 0–100 kHz range. Sensitivity of first and second bending mode resonances was characterized in a flow apparatus using small density changes in liquid (0.003–0.01 g/cm3) and by dodecanethiol chemisorption at 30 pM. Density change results were consistent with existing models of submerged cantilevers, and yielded mass-change sensitivity of ∼33 ng/Hz and 217 pg/Hz for the first two modes. In chemisorption experiments, where binding was localized to 1 mm2 distal tip of the PZT cantilever, sensitivity improved by an order of magnitude to 2 pg/Hz and 414 fg/Hz for the same two resonant modes.