Possibility of a femtogram mass biosensor using a self-sensing cantilever

The possibility of realizing femtogram mass detection using a piezoresistive microcantilever has been studied for bioscience applications. The mass detection was undertaken by employing the resonance frequency shift of a cantilever. In the experiments, we measured the change in the mass of adsorbed water molecules and the reaction between an antigen and an antibody on the cantilever from the resonance frequency shift. We used a prototype and a commercially available piezoresistive cantilever. The sensor was formed by using Wheatstone bridge circuits, a positive feedback controller, a piezoactuator and a phase-locked loop (PLL) demodulator. A mass sensitivity of around 200 fg/Hz and a noise level of about 12 fg were estimated experimentally from the water molecules adsorbed on the cantilever. We also confirmed that the sensor could detect an antigen and antibody reaction in an egg allergy test.