Capacitive micromachined ultrasound transducers (CMUT) for resonant gravimetric immunosensing

The array of the CMUT sensors was fabricated by the direct bonding of the silicon membranes provided as a device layer of the SOI wafer with the oxidized and pre-patterned highly doped silicon wafer. The active surface of the sensors was coated with thin gold film. We demonstrate the detection of the formed immune complex over the CMUT surface modified by the bovine leukemia virus antigen BLV gp51. The modified CMUT surface was allowed to interact with the specific antibody anti-gp51 labeled by the horseradish peroxidase. Antibody labels were actvated after the interaction by wetting the sensor surface with tetramethylbenzidine to provide the reference quantification of the formation of the immune complex. CMUT sensor readings (resonance frequency and the resonance value of the impedance real part, “resistance”) were obtained before and after modification by the BLV gp51 and after the interaction with antig-p51. The readings were interpreted and fitted by the finite element analysis. It was determined that increase of the elasticity modulus and stress of the sensor structure caused increase of the resonance frequency and some decrease of the resonance quality (resistance value). After the immune complex is established, we observe decrease of the resonance frequency by 4% on average from the initial value. Finite element analysis model fitting to the experimental results revealed the mass loading function of the CMUT structure in the presence of increased elasticity of the proteins.