Accurately measuring cortisol levels is crucial for diagnosing and managing stress-related conditions. Among all biofluids containing cortisol, Interstitial fluid (ISF) offers distinct advantages such as stable pH, continuous extraction, and minimal contamination risks. This study introduces a novel method utilizing an AC driven liquid-gate Graphene Field Effect Transistor (GFET) array device, decorated with a cortisol aptamer for precise cortisol detection from changes in GFETs' phase to address challenges encountered in DC measurements, including the Debye length screening effect and noise issues. Aptamers, selected for their compact size and ease of synthesis, serve as optimal recognition elements that also show capacitive changes. The proposed sensor demonstrates very strong linear detection ranges 1 nM to 1 μ M with sensitivity of 3.34 mV/dec (R2=0.94) for cortisol concentrations in 1XPBS. This effectively covers the physiological cortisol range in ISF, even in high ionic backgrounds. In this work, Graphene functionalization was validated using Raman spectroscopy and AFM-SNOM. The integration of AC voltage driven liquid-gate GFETs with aptamers shows promise for advancing 2D sensors in personalized healthcare technology. Keywords: GFET, graphene, aptamer, cortisol.