Determination of liquid viscosity based on dual-frequency-band particle tracking

An optical-tweezers-based dual-frequency-band particle tracking system was designed and fabricated for liquid viscosity detection. On the basis of the liquid viscosity dependent model of the particle’s restricted Brownian motion with the Faxén correction taken into account, the liquid viscosity and optical trap stiffness were determined by fitting the theoretical prediction with the measured power spectral densities of the particle’s displacement and velocity that were derived from the dual-frequency-band particle tracking data. When the SiO₂ beads were employed as probe particles in the measurements of different kinds of liquids, the measurement results exhibit a good agreement with the reported results, as well as a detection uncertainty better than 4.6%. This kind of noninvasive economical technique can be applied in diverse environments for both in situ and ex situ viscosity detection of liquids.