Detection of S. Typhimirium and Bacillus Anthracis Spores in a Flow System Using ME Biosensors by Optimizing Phage Chemistry

This paper presents the results of a study that investigates the optimization of phage chemistry during the fabrication of magnetoelastic (ME) biosensors for the detection of Salmonella typhimurium or Bacillus anthracis spores. The bundling characteristics of the phage filaments limit the ability of the biosensor to bind bacterial cells/spores. Experiments were performed to determine the proper phage concentration for the prevention of bundling in aqueous environments. Based on the transmission electron microscopy (TEM) and scanning electron microscopy (SEM) results, which verify the structure of phage under different concentrations and binding numbers of target species to the sensor surface, we found that phage concentrations of 10¹¹ vir/ml exhibit the best sensor performance in terms of binding sensitivity. Additionally, the sensors immobilized with phage under this condition were tested in a flowing liquid system using S. typhimurium and B. anthracis spores suspensions in concentrations ranging from 5 times10¹ to 5 times 10⁸ cfu/ml, separately. As cells/spores are bound to a ME biosensor surface, the additional mass of the spores causes a decrease in the resonance frequency of the sensor. The frequency response curves of the ME biosensors as a function of exposure time were then measured, and the detection limit of the ME biosensor was determined to be 5 times 10³ cfu/ml.