Computational design of quartz crystal nanobalance for uniform sensitivity distribution

Abstract

The mass sensitivity (> 1 micrograms) of current commercial analytical instruments, such as thermal gravimetric analyzers, severely limits their utility for measurement of valuable but poorly soluble materials such as synthetic proteins or DNA fragments. A quartz crystal microbalance (QCM), based on a transverse shear mode piezoelectric crystal operating at high frequencies, is gaining popularity in chemical and bio-sensing applications due to higher mass sensitivities as compared to the traditional analyzers and lesser sensitivity to vibrations. However, these devices suffer from non-uniformity of sensitivity distribution along the sensor surface thereby limiting their use for the determination of mass. Overcoming this limitation would lead to the development of a robust sensor with improved mass sensitivities and reduced sensitivity to vibrations, as compared to the currently available microbalances. The sensitivity profile can be influenced by a number of factors the electrode design and surface properties of the crystal. In the current work, we develop a finite element (FE) model of the QCM to investigate the mass sensitivity and its radial distribution on the sensor surface for various electrode designs. Such a model will aid in the development of versatile nano-balances with a uniform sensitivity distribution.