  The quartz crystal microbalance (QCM) is widely used to study surface
adsorbed molecules, often of biological significance. However, the relation
between raw acoustic response (frequency shift $\Delta f$ and dissipation
factor $\Delta D$) and mechanical properties of the macromolecules still needs
to be deciphered, particularly in the case of suspended discrete particles. We
study the QCM response of suspended liposomes tethered to the resonator wall by
double stranded DNA, with the other end attached to surface-adsorbed
neutravidin through a biotin linker. Liposome radius and dsDNA contour length
are comparable to the wave penetration depth ($\delta\sim 100\ \mathrm{nm}$).
Simulations, based on the immersed boundary method and an elastic network model
for the liposome-DNA complex, are in good agreement with experimental results
for POPC liposomes. We find that the added stress at the resonator surface,
i.e. the impedance Z sensed by QCM, is dominated by the flow-induced liposome
surface-stress, which propagates towards the resonator by viscous forces. QCM
signals are extremely sensitive to the liposome's height distribution P(y)
which depends on the actual number and mechanical properties of the tethers, in
addition to the usual local attractive/repulsive chemical forces. Our approach
helps in deciphering the role of hydrodynamics in acoustic sensing and
revealing the role of parameters hitherto largely unexplored. A practical
consequence would be the design of improved biosensors and detection schemes.
