Development of carbon-based biocompatible and flexible nanosensors is essential in different practical applications. Humidity sensor is crucial in different fields among them. Herein, a unique metal-free nanosensor comprised of 2D-graphitic carbon nitride (CN) decorated with 0D-carbon dots (C-dots) was fabricated to monitor humidity in human breath. Simple polymerization and carbonization techniques were used to synthesize nitrogen enriched heterostructure (CN@C-dots). The synthesized heterostructure showed excellent physicochemical properties including high surface area, hydrophilic functionalities and more active sites that were responsible for enhanced humidity sensing. The fabricated nanosensor indicated excellent resistivity against humidity due to diffused proton hoping through inhibition of ion transfer from multiple water layers. The interaction mechanism was explained through simple hydrogen bonding and defective site chemisorbed oxygen participation in physisorbed humidity molecules.