We have performed particle aggregation characterization on the basis of their material and suspending
medium in a capillary-based cavity resonator used for acoustophoresis. We have investigated the experimental
aggregation time of 5μm polystyrene and silica particles, size of aggregate, number of trapped particles and upconcentration
factor in water, 0.01M phosphate buffered saline (PBS) and 0.005M PBS at 1.97MHz and with
actuation voltages between 4, 8 and 12Vpp. We have found that there is little difference between using water and
PBS as suspension medium, approximately 5-10% longer trapping times with PBS compared with water.
However we get approx. 5.5 times faster trapping time for silica than for polystyrene. It is also observed and
calculated that silica particle aggregates have 3.4 times larger area than the polystyrene aggregates using the same
starting particle concentrations, revealing similar amount of difference in trapped number of particles. The upconcentration
factor for silica is also about 3.2 times higher than that of polystyrene due to larger aggregate area
of silica particles. Based on theoretical predictions and experimental characterization of the particle aggregation
pattern, we note that the particle-particle interaction force contribution to the total acoustic radiation force is more
pronounced for silica than for polystyrene. Finally as a proof of principle for biomedical sample preparation
application we demonstrate the capillary-based silica particles mediated bacteria acoustophoretic upconcentration.
This setup could potentially be utilized not only for sample preparation application but also for
bead based affinity immunoassays.