3.3. Limit of detection To determine the limit of detection of the FTIR based nanobiosensor for E.coli described here, we immobilized the different concentration of antigen as 100 μg/mL, 50 μg/mL, 25 μg/mL and 10 μg/mL on to the graphene membrane as shown in Fig. 5. It is clearly stated from Fig. 5. The film-based biosensors developed by Stefania Mura at el.showed a detection limit for E. coli of 1 × 102 CFU/mL [23]. Furthermore, a technique has been demonstrated to precisely detect E-coli by using AntiE. coli β-gal antibody within a detection limit of 10 μg/ml. The calculated sensitivity is shown in Fig. 6 using linear relationship of intensity vs concentration. This linear curve is fitted by y = 4642.5× + 41.5, where y is the intensity and x is E.coli concentration. The sensitivity of nanobiosensor platform was calculated 0.035 cd-gml−1 cm−1 at biosensing surface area of 1.32 cm2