Abstract: Embodiments herein relate to chemical sensors based on the non-covalent surface modification of graphene with compounds containing hydrazine or hydroxylamine functional groups for the detection of aldehyde and ketone-bearing analytes. In an embodiment, a medical device is included having a graphene varactor included a graphene layer and a self-assembled monolayer disposed on an outer surface of the graphene layer through electrostatic interactions between a partial positive charge on hydrogen atoms of one or more hydrocarbons of the self-assembled monolayer and a ?-electron system of graphene. The self-assembled monolayer can include one or more compounds having one or more hydrazine groups or hydroxylamine groups, substituted hydrazine or hydroxylamine groups, or derivatives thereof. Other embodiments are also included herein.