(120e) Atomic Force Microscopy Study Of Immobilized Bacteriophage And Its Interactions With Bacteria

Currently, antibodies are the most commonly used sensing elements in biosensors for the detection of biomolecules and organisms. Alternatively, we focus on the use bacteriophages to detect harmful waterborne organisms such as Salmonella due to their temperature and pH resilience. A silane (APTMS) layer is used as a bifunctional cross linker to covalently bind the phage to a glass substrate using sulfo-NHS and EDC chemistry. Using AFM we have shown that the phage P22 displays specific binding affinity to bacteria Salmonella typhimurium. Salmonella typhimurium is a gram negative bacterium whose outer membrane is made of lipopolysaccharide (LPS). P22 specifically binds to the repetitive O antigen part present in the LPS of Salmonella. The binding affinity is determined both by imaging the amount of bacteria deposited on P22, and by single molecular unbinding force measurements between P22-modified AFM tips and LPS-modified glass substrates. Discrete unbinding forces are obtained as a function of pH, ionic strength, and temperature. Affinity of Salmonella to aged P22 is compared to freshly prepared P22 in order to demonstrate the durability of phage-based biosensors.