Expression of picogram sensitive bending modes in piezoelectric cantilever sensors with nonuniform electric fields generated by asymmetric electrodes.

Single-layer uniform cross-sectioned piezoelectric macro-cantilevers fabricated with an asymmetric electrode configuration enabled electrical measurement of picogram-sensitive resonant bending modes in liquids. Bending modes were otherwise not electrically measurable without excitation by a nonuniform electric field created by the geometric asymmetry in electrode design used. Electrode modification was confirmed by energy-dispersive X-ray spectroscopy (EDS). Mass-change sensitivity was tested using both bulk density changes and surface chemisorption experiments in a continuous flow apparatus. Significant response to density changes as small as 0.004 g/mL was measured. A sensitivity limit of ∼1 picogram in liquid was determined from 1-dodecanethiol chemisorption experiments. The sensitivity decreased with chemisorbed mass and was log-linear over five orders of magnitude. The observed resonance responses were in agreement with previously reported models of resonating cantilever sensors. This work demonstrates experimentally for the first time that introducing electrode asymmetry enables measurement of bending modes in cantilevers containing only a single piezoelectric layer.