PEMC sensor's mass change sensitivity is 20 pg/Hz under liquid immersion

To enhance the mass change sensitivity of the resonating piezoelectric-excited millimeter-sized cantilever (PEMC) sensors, we reduced its length and eliminated one layer of its composite structure. As a result the mass sensitivity of the second flexural mode increased by two orders of magnitude (from 10−9 to 10−11 g/Hz) and the resonant frequency increased by more than 5 kHz. We demonstrate the effects of modification by detecting a model pathogen Group A Streptococcus (GAS) at 700 cells/mL. The resonant frequency change of the second mode at concentrations of 700, 7 × 103, 7 × 105, 7 × 106, 7 × 107, and 7 × 109 cells/mL resulted in, respectively, 3.1 ± 0.5, 11.6 ± 1, 15.7 ± 1, 25.7 ± 0.15, 28.5 ± 2, and 40.5 ± 3 ng (n = 3 for all) of pathogen attachment. A kinetic model for the binding is proposed and verified. The observed binding rate constant was found to be in the range of 0.051–0.166 min−1. The significance of the results we report is that the modified PEMC sensors have high mass sensitivity that pathogens can be detected at very low concentration under liquid immersion conditions.