In this paper, we present a double gate JL-TFET based biosensor by varying the gate dielectric constant to detect various biomolecules through label-free detection technique. An investigation regarding properties and behavior device has been investigated with the help of Silvaco TCAD. It is observed that Junction less TFET has advantageous over JLFET and TFETdue to the absence of junctions. The proposed device shows reduced short channel effects, lower subthreshold swing along with a higher voltage gain. The detection of the biomolecule is done by varying the gate dielectric constant inside the cavity and different electrical parameters such as electric field, sensing current, threshold voltage and transconductance are observed. The change in the threshold voltage, drain current, transconductance has been used as the sensing metric to detect the sensitivity of the presented device for biomolecule detection. Biomolecule position inside the cavity have been investigated to find out their effect on sensitivity parameter.