Resonances of bare cantilevers, cantilevers after peptide immobilization, and such peptide-immobilized cantilevers after exposure to protease with protease concentrations of 0.28 µM, 1.12 µM, 1.53 µM, and 1.61 µM, respectively, were measured in dry air or liquid (only for Cantilever 1).

From Eq. (3), the total amount of immobilized peptides and cleft peptides, respectively, were also computed. Here, ω0, ΔωI, ΔωP, ΔmI, and ΔmP indicate the resonant frequency of a bare cantilever, the resonant frequency shift due to peptide immobilization, the resonant frequency shift induced by proteolysis by protease, the total mass of immobilized peptides on cantilever's surface, and the total amount of cleft peptides due to protease with a given protease concentration [CTSB], respectively. The positive sign in the resonant frequency shift indicates the increase of the resonance, while the negative sign shows the decrease of the resonance.