  Graphene, a 2-dimensional monolayer form of sp2 hybridizated carbon atoms, is
attracting increasing attention due to its unique and superior physicochemical
properties. Covalently functionalized graphene layers, with their modifiable
chemical functionality and usefull electrical properties, are excellent
candidates for broad range of sensors, suitable for biomedical, optoelectronic
and environmental applications. Here, we present extensive study of transport
properties of sensors based on covalently functionalized graphene monolayer
(GML) with graphene electrodes. The transmissions, density of states and
current-voltage characterisctics supported by analysis of charge distribution
of GML functionalized by -CH3, -CH2, -NH2, -NH and -OH fragments have been
calculated by means of density functional theory (DFT) and non-equilibrium
Green's function (NEGF). Further, we demonstrate how to control the device
sensitivity by manipulating: (i) concentration, (ii) particular arrangement,
and (iii) type of surface groups. We explain the underlying detection physical
mechanisms. Comparisons of the theoretical results to available experimental
data are provided are made and show good agreement.
