Chemical sensors with non-covalent surface modification of graphene

A medical device comprising:

• a graphene varactor comprising:
• a graphene layer;
• a self-assembled monolayer disposed on an outer surface of the graphene layer through π-π stacking interactions;
• and
• wherein the self-assembled monolayer provides a Langmuir theta value of at least 0.9;
• wherein the self-assembled monolayer comprises at least one metallotetraphenylporphyrin compound having the formula
• wherein M is any metal atom comprising aluminum, calcium, magnesium, manganese, iron, cobalt, nickel, zinc, ruthenium, palladium, or derivatives thereof;
• where n can be any integer from 1 to 5;
• m can be 1 or 2;
• R1 through R8 comprise —H;
• —X, where X is any halogen atom;
• —R9;
• —R10OH;
• —R11COOH;
• —R12COOR13;
• —R14OR15;
• —R16COH;
• —R17COR18;
• —R19NH3+;
• —R20NH2;
• —R21NR22;
• —R23NR24R25+;
• —R26X or —R27COX, where X is any halogen atom;
• —R28SH or any combination thereof;
• and R9, through R28 comprise any linear or branched C1-C12 alkyl, C1-C12 alkenyl, C1-C12 alkynyl, or any combination thereof, or can be absent such that the remaining portion of the functional group is covalently bound directly to one or more carbon atoms of the base aromatic ring structure.