  Renowned for its sensitivity to detect the presence of numerous substances,
graphene is an excellent chemical sensor. Unfortunately, which general features
a dopant must have in order to enter the list of substances detectable by
graphene are not exactly known. Here we demonstrate with a simple model
calculation implemented in three different ways that one of such features is
the symmetry properties of the impurity binding to graphene. In particular, we
show that electronic scattering is suppressed when dopants are bound
symmetrically to both graphene sub-lattices, giving rise to impurity
invisibility. In contrast, dopants that affect the two sublattices
asymmetrically are more strongly scattered and therefore the most likely
candidates to being chemically sensed by graphene. Furthermore, we demonstrate
that impurity invisibility is lifted with the introduction of a
symmetry-breaking perturbation such as uniaxial strain. In this case, graphene
with sublattice-symmetric dopants will function as efficient strain sensors. We
argue that by classifying dopants through their bonding symmetry leads to a
more efficient way of identifying suitable components for graphene-based
sensors.
