Femtogram mass biosensor using self-sensing cantilever for allergy check

A self-sensing mass biosensor with a femtogram mass sensitivity has been developed using a piezoresistive microcantilever. The mass change due to antigen and antibody adsorption oil the cantilever in water was detected by the resonance frequency shift of the cantilever. We constructed a prototype harmonic vibration sensor using a commercial piezoresistive cantilever, Wheatstone bridge circuits, a positive feedback controller, an exciting piezoacutuator and a phase-locked loop (PLL) demodulator. As experimental results, a mass sensitivity of about 190 fg/Hz, and a mass resolution of about 500 fg were obtained in water. The mass sensitivity is 100 times higher than that of a quartz crystal oscillation method. We demonstrated that the sensor can detect the reaction between an antibody of immunoglobulin (IgG) and ail antigen of egg albumen (OVA). We confirmed that the binding ratio between the antibody and the antigen was about 1 : 2. The detection method is available for allergy check because the measured reaction ratio occurring oil the cantilever concurs with the theoretical method.