We report on highly sensitive and flexible L-lactate enzymatic sensors. The sensing materials of this biosensor, two-dimensional (2D) zinc oxide nanoflakes (ZnO NFs), are synthesized on flexible gold(Au)-coated polyethylene terephthalate (PET) substrate using one step sonochemical approach for non-invasive lactate monitoring in human perspiration. ZnO NFs show high isoelectric points (IEP) and biocompatibility. Taking advantage of these unique properties, we immobilized Lactate oxidase (LOx) on the synthesized ZnO NFs. PET/Au/ZnO NFs sensors demonstrated detection of lactate in the range of 10 pM-10 µM for the electrode area of 0.5×0.5 cm2. The sensitivity of this linker free lactate sensor was found 2.23μA/M /cm2 and shows 4 times better response than conventional Au electrode with linker.