Lipopolysaccharides are a distinguishing feature of gram negative bacterial surfaces. Antibodies that recognize and distinguish between different O-specific oligosaccharide units are used to identify pathogenic bacterial strains that are been found in contaminated foods and have caused human death and disease. LPS molecules are often intimately involved in pathogenesis and participate in functions such as bacterial adhesion and movement, and in eliciting autoimmune responses. Septic shock syndrome, a severe inflammatory response that is often elicited by LPS, is deadly, killing 40% of individuals with symptoms. Recognition that pathogenic bacteria are deadly, easily dispersed and could be used for bioterrorism emphasizes the need to readily detect pathogenic bacteria and of having antidotes to protect against them. Antibodies are a very important means of detecting specific LPS molecules. However, the production and specificity of antibodies is expense and results can be variable. On occasion, antibodies are also cross-reactive between two LPS structures or with carbohydrates in human tissues and thus have limited use. Here we propose to develop aptamers that recognize specific LPS structures. Aptamers are nucleic acids that, like antibodies, specifically recognize with high affinity the target macromolecules against which they were selected. Unlike antibodies, aptamers are selected ex-vivo and consequently can be more readily modified than antibodies so as to possess particular desired characteristics. Aptamers also possess many characteristics that are advantageous for diagnostics and field work. Our long term goal for anti-LPS aptamers is that they will add a new dimension to the ability to detect LPS from bacterial surfaces and that these aptamers also might find use in passive immunity or in other medical applications. We foresee the use of aptamers in homogeneous assays and in microarrays for on location detection of pathogens as a part of future in-place detection systems in public spaces for early detection of bioterrorist activities. The specific aims for this application are to: 1) Select for aptamers that bind LPS with high specificity and high affinity, 2) Characterize the selected aptamers, 3) Develop an allosteric aptamer CLAMP that detects a specific LPS oligosaccharide.