This paper presents a radio-frequency (RF) antenna as a sensor to detect Horseradish peroxidase (HRP). At the core of the proposed approach is a graphene film deposited on a stub connected to an RF antenna. The graphene film is doctor bladed on the stub. The film is then properly chemically functionalized in order to detect the presence of Horseradish peroxidase (HRP). We validate the proof-of-concept operation of HRP concentration detection by measuring the frequency shift of the reflection coefficient of the antenna using very small concentration of HRP (0.03 mM to 0.6 mM).