▎ 摘　　要

NOVELTY - A medical device comprises a graphene varactor (100) comprising a graphene layer (108), and a self-assembled monolayer arranged on an outer surface (101) of the graphene layer through electrostatic interactions between a partial positive charge on hydrogen atoms of hydrocarbons of the self-assembled monolayer and a pi -electron system of graphene. The self-assembled monolayer comprises substituted porphyrins or substituted metalloporphyrins, or its derivatives. USE - Medical device is used for detecting analyte (claimed) e.g. volatile organic compounds in gaseous sample derived from patient, preferably breath of patient. ADVANTAGE - The medical device detects the analyte in gaseous sample without adverse impact on readings, and has high sensitivity for volatile organic compounds. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following: (1) modification of surface of graphene to create a graphene varactor, which involves forming self-assembled monolayer on the outer surface of the graphene layer, and quantifying the extent of surface coverage of the self-assembled monolayer using contact angle goniometry, Raman spectroscopy, or X-Ray photoelectron spectroscopy; and (2) detection of analyte, which involves collecting a gaseous sample from a patient, and contacting the gaseous sample with graphene varactors. DESCRIPTION OF DRAWING(S) - The drawing shows a schematic perspective view of the graphene varactor. Graphene varactor (100) Graphene surface (101) Insulator layer (102) Gate electrode (104) Graphene layer (108)