2.4. Antibody immobilization An antibody solution was prepared from a 1.7 mg/ml stock by dissolving 100 μl of anti-E. coli (β-gal) in 900 μl of PBS to achieve a final concentration of 170 μg/ml, after which the GO-coated membrane was covered with this solution and incubated for 15 h at 4 °C. 3. Results and discussion 3.1. Characterization of GO-coated membranes The normal and GO-coated PCTE membranes were placed on a Petri dish (Borosil) one-by-one and the micrograph was recorded using inverted microscopy (40×), SEM, and TGA (see Section 2.2, Methods section). The results are presented in Figs. 1–5. Fig. 1 is a pictorial depiction of micrographical representation of GO-PCTE membrane fitted in membrane holder cell with different micrographs wherein Fig. 1a shows an image of the liquid cell used to hold the PCTE membrane. The micrograph in Fig. 1b depicts the grey surface structure of the normal membrane; whereas the micrograph of GO-coated membrane surface shows the golden brown colour of GO on the surface of the polycarbonate membrane as shown in Fig. 1c. Therefore, bright-field image analysis clearly demonstrates that the GO is uniformly coated over the surface of the membrane. The GO coating onto the PCTE membrane was further confirmed by SEM showed Fig. 1d. The SEM micrograph of GO-coated PCTE membrane is represented at 15.00 kX magnifications with a SE1 detector and EHT at 20.00 kV. The SEM micrograph of the normal PCTE membrane represented in Fig. 1e, at 1.00 kX magnification with a SE1 detector and EHT at 20.00 kV, shows a black uniform layer of GO over the surface of the nano-porous membrane and the absence of nanopores due to the healing of the surface by the Fig. 1. (a) Liquid cell holder with mounted PCTE membrane. (b) Inverted microsc