Rapid Detection of Live Versus Dead Bacteria

Abstract

This paper presents a rapid method of detecting live versus dead pathogenic bacteria. The method combines phage-coated magnetoelastic (ME) biosensors and a wireless planar coil detector, enabling real-time monitoring of the growth and viability of specific bacteria in a nutrient broth. The ME biosensor used in this investigation is composed of a strip-shaped ME resonator (1 mm x 0.2 mm x 30 um) upon which a landscape phage is coated to capture specific bacteria. E2 phage with high binding affinity for Salmonella Typhimurium was used as a model study. The specificity of E2 phage has been reported to be 200 in 108 background bacteria. When the binding of Salmonella occurs, the mass of the biosensor increases, which simultaneously results in a decrease in the biosensor's resonant frequency. Monitoring of this mass-induced resonant frequency change allows for the instantaneous detection and quantification of Salmonella. ME biosensors with a pre-determined resonant frequency were first exposed to a low-concentration Salmonella suspension to capture a small but detectable amount of the bacteria on the sensor surface. The wireless coil detector was then used to measure the resonant frequency changes of the biosensors as a function of time in a nutrient broth. Live cells can grow, while dead ones can't, which leads to distinct differences in the resonant frequency changes over time. Hence, this methodology offers direct, real-time detection, quantification, and viability determination of specific bacteria.