A membrane strip biosensor device (10, 20, 100) using a fluid mobile conductive composition of ferromagnetic particles bound to a conductive polymer bound to a capture reagent is described. The biosensor device is designed to detect analytes at low concentrations in near real-time with an electronic data collection system and can be small. The device can be used to detect pathogens, proteins, and other biological materials of interest in food, water, and environmental samples. The device can also be used for on-site diagnosis and against potential bioterrorism. Potential users include food processing plants, meat packaging facilities, fruit and vegetable packers, restaurants, food and water safety inspectors, food wholesalers and retailers, farms, homes, medical profession, import border crossing personnel, and the police force, military, space habitation and national security.