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Thin-film silicon MEMS microresonators for DNA and protein detection
Thin-film MEMS molecular sensors are fabricated at temperatures below 110șC on glass substrates. The microelectromechanical structure consists of a surface micromachined bilayer bridge of phosphorous-doped hydrogenated amorphous silicon and aluminum with a patterned SiO2 layer on the top. Specific binding of DNA to functionalized SiO2 on the bridge is confirmed using fluorescence microscopy. Microbridges are electrostatically actuated and the resonance frequency measurements are performed in vacuum in the initial state after fabrication, after the chemical functionalization of the SiO2 surface and after DNA immobilization. The sensor is able to detect the functionalization molecular layer, the cross-linker molecular layer, and the DNA molecules attached to the surface through a shift in its resonance frequency. The binding of molecules to the surface results in a shift of the resonance frequency due to contributions from surface stresses and mass loading. These studies are being extended to the adsorption of antibody proteins and their specific antigens. Thin film silicon MEMS thus far have sensitivity in the pmol/cm2 range.
Adsorption of antibodies on amorphous silicon MEMS induces a shift in the resonance frequency. The figure on the right highlights the effect of the decreasing Q with dissipation on the BioMEMS sensitivity.