  Graphene has attracted significant interest both for exploring fundamental
science and for a wide range of technological applications. Chemical vapor
deposition (CVD) is currently the only working approach to grow graphene at
wafer scale, which is required for industrial applications. Unfortunately, CVD
graphene is intrinsically polycrystalline, with pristine graphene grains
stitched together by disordered grain boundaries, which can be either a
blessing or a curse. On the one hand, grain boundaries are expected to degrade
the electrical and mechanical properties of polycrystalline graphene, rendering
the material undesirable for many applications. On the other hand, they exhibit
an increased chemical reactivity, suggesting their potential application to
sensing or as templates for synthesis of one-dimensional materials. Therefore,
it is important to gain a deeper understanding of the structure and properties
of graphene grain boundaries. Here, we review experimental progress on
identification and electrical and chemical characterization of graphene grain
boundaries. We use numerical simulations and transport measurements to
demonstrate that electrical properties and chemical modification of graphene
grain boundaries are strongly correlated. This not only provides guidelines for
the improvement of graphene devices, but also opens a new research area of
engineering graphene grain boundaries for highly sensitive electrobiochemical
devices.
