Detection and quantification of proteins using self-excited PZT-glass millimeter-sized cantilever.

A composite self-excited PZT-glass cantilever (4mm in length and 2mm wide) was fabricated and used to measure the binding and unbinding of model proteins. A key feature of the cantilever is that its resonant frequency is dependent on its mass. The fabricated cantilever has mass change sensitivity in liquid of 7.2 x 10(-11)g/Hz. Resonant frequency change was measured as protein reacted or bound with the sensing glass cantilever surface. Protein concentrations, 0.1 and 1.0mg/mL, which resulted in nanogram mass change were successfully detected. The mass change sensitivity gave a total mass change of 54+/-0.45 ng for the binding of anti-rabbit IgG (biotin conjugated) to rabbit IgG immobilized cantilever and the subsequent binding of captavidin. The unbinding of anti-rabbit IgG and captavidin gave a total mass change of 54+/-1.70 ng. Fluorescence based assays showed the combined mass of both proteins in the released samples was 54+/-2.24 ng. The binding kinetics of the model proteins is modeled as first order. The initial binding rate constant of anti-rabbit IgG to rabbit IgG was 1.36+/-0.02(min(mg/mL))(-1). The initial binding rate constant of captavidin to biotinylated anti-rabbit IgG was (2.57 x 10(-1))+/-0.003(min(mg/mL))(-1). The significance of the results we report here is that millimeter-sized PZT-actuated glass cantilevers have the sensitivity to measure in real-time protein-protein binding, and the binding rate constant.