A method of immobilizing and stabilizing an active biological receptor in a polymeric film and receptor-based biosensors for determining an analyte of interest in a sample. The receptor-based biosensors include a polymeric film having a biological receptor capable of binding an analyte of interest immobilized therein according to the method of the present invention and an electrical means for determining the presence and quantity of the analyte. In particular, acetylcholine receptor and opiate receptor have been immobilized in a polymeric film made by combining the receptor, a material (e.g., bovine serum albumin, gelatin) capable of polymerizing and a polymerizing agent (e.g., glutaradehyde).