microbalance

A microbalance is a highly sensitive mass-sensing device capable of detecting very small changes in mass, often in the nanogram to picogram range. Most microbalances convert a mass change into an electrical signal by measuring either a change in the resonant frequency of a miniature oscillator or the deflection of a sensing element. The relationship between frequency shift and added mass is described in first-order terms by the Sauerbrey equation for thin, rigid, uniform films on a piezoelectric crystal.

Quartz crystal microbalances (QCM) are the most widely used type. They employ a thin piezoelectric quartz crystal that resonates at a characteristic frequency; when mass adheres to the crystal surface, the frequency decreases. Advances such as quartz crystal microbalance with dissipation monitoring (QCM-D) add measurements of energy dissipation to assess the viscoelastic properties of the deposited layer, enabling more accurate interpretation in liquids and soft films. Microcantilever-based balances, another class, detect mass via the bending of a cantilever, typically measured optically or by integrated sensors.

Applications span thin-film deposition monitoring, surface science, and biosensing. In film growth and material science, microbalances track adsorption and deposition rates in real time. In biology, they enable label-free detection of biomolecular interactions, such as protein binding or DNA hybridization. In liquids, the interpretation becomes more complex due to viscoelastic loading, requiring appropriate models and careful temperature control.

Limitations include sensitivity to environmental conditions, especially temperature and viscosity, and the validity of the mass-to-frequency relation for non-rigid or heterogeneous layers. Nevertheless, microbalances provide real-time, non-destructive mass measurements across research and industry.