The existence of terrorist organizations around the world, along with their ability to recruit expertise from physicians and scientists, poses an increasing threat of bioterrorist attack to society. In order to reduce the consequences of such an attack or even prevent it, new systems for detection of biothreat agents are necessary. Currently existing "express" methods suffer from either being too expensive and complicated or lacking sensitivity. In contrast, we propose to develop a new system that will be inexpensive, simple to use, and highly sensitive. This system will be created by combining a novel signal amplification approach, developed in our lab, with advances in directed protein evolution. To prove the viability of our approach, during Phase I, we will develop the first components of this detection system targeted at the receptor- recognizing domain of Botulinum Neurotoxin Serotype A. In Phase II, this approach will be used to develop additional detectors for a universal Botulinum Neurotoxin detection system.