Selective protein channels in cell and nuclear membranes act as gateways to control the passage of molecules across. The selectivity of these channels stems from attractive potentials of the binding sites in the transmembrane proteins. These channels can filter out small volume of solutions with high precision. Motivated from this phenomenon, we report biomimetic facilitated transport modality to selectively separate a target molecule from a mixture of molecules. The attractive potential is generated by specific antibodies immobilized inside 15 nm diameter polycarbonate nanochannels. Two proteins with similar physicochemical properties (Bovine Serum Albumin 66 kDa, and Human Hemoglobin 65 kDa) are chosen as model molecules. The protein molecules are mixed in ratios of 1:1, 1:20 and 1:40 (Hb:BSA), and separation of molecules is demonstrated. The selectivity of membrane can be switched from Hb to BSA by changing the immobilized antibody inside the membrane channels. This approach can be used to selectively enrich any target molecule from a complex sample to enhance signal-to-noise ratio for early disease diagnosis.