  In this Letter, using quartz crystal microbalance (QCM), we experimentally
determined the mass density of graphene grown by chemical vapor deposition
method. We developed a transfer printing technique to integrate large area
single-layer graphene on QCM. By monitoring the resonant frequency of an
oscillating quartz crystal loaded with graphene, we were able to measure the
mass density of graphene as ~118 ng/cm2, which is significantly larger than the
ideal graphene (~76 ng/cm2) mainly due to the presence of wrinkles and
organic/inorganic residues on graphene sheets. High sensitivity of quartz
crystal resonator allowed us to determine the number of graphene layers in
samples. (The technique is very sensitive and able to determine the number of
graphene layers in a particular sample.) Besides, we extended our technique to
probe interfacial mass variation during adsorption of biomolecules on graphene
surface, and plasma-assisted oxidation of graphene. (Besides, we extended our
technique to probe interfacial mass variation during adsorption of biomolecules
on graphene surface, and plasma-assisted oxidation of graphene.)
