Tuning forks as micromechanical mass sensitive sensors for bio- or liquid detection

The low frequency mechanical resonators (quartz tuning forks, 32,768 Hz) have been developed to detect the mass loading due to thin solid films or Newtonian liquids. First, the simplified cantilever model was introduced to analog the performance of tuning forks. The mass loading sensitivity have been introduced and compared with the quartz crystal microbalance (QCM). Experimentally, two kinds of excitation modes, called self-feedback driving and externally passive driving, have been investigated to drive the forks for various sensing applications. The theoretical and measured sensitivity of mass loading is ∼75 and ∼100 Hz/μg, respectively, which is comparable with the conventional QCM (∼1 Hz/ng) since high-precision low frequency measurement (with accuracy of ∼0.01 Hz) is easier to achieve. The tuning forks also can act as a chemical sensor working in the liquids. At last, the tuning forks had been used as both the biosensors for antigen–antibody affinity detection and the chemical sensors for liquid density detection.