Sequential detection of Salmonella typhimurium and Bacillus anthracis spores using magnetoelastic biosensors.

Multiple phage-based magnetoelastic (ME) biosensors were simultaneously monitored for the detection of different biological pathogens that were sequentially introduced to the measurement system. The biosensors were formed by immobilizing phage and 1mg/ml BSA (blocking agent) onto the magnetoelastic resonator's surface. The detection system included a reference sensor as a control, an E2 phage-coated sensor specific to S. typhimurium, and a JRB7 phage-coated sensor specific to B. anthracis spores. The sensors were free standing during the test, being held in place by a magnetic field. Upon sequential exposure to single pathogenic solutions, only the biosensor coated with the corresponding specific phage responded. As the cells/spores were captured by the specific phage-coated sensor, the mass of the sensor increased, resulting in a decrease in the sensor's resonance frequency. Additionally, non-specific binding was effectively eliminated by BSA blocking and was verified by the reference sensor, which showed no frequency shift. Scanning electron microscopy was used to visually verify the interaction of each biosensor with its target analyte. The results demonstrate that multiple magnetoelastic sensors may be simultaneously monitored to detect specifically targeted pathogenic species with good selectivity. This research is the first stage of an ongoing effort to simultaneously detect the presence of multiple pathogens in a complex analyte.

The effect of salt and phage concentrations on the binding sensitivity of magnetoelastic biosensors for Bacillus anthracis detection.

This article presents an investigation of the effect of salt and phage concentrations on the binding affinity of magnetoelastic (ME) biosensors. The sensors were fabricated by immobilizing filamentous phage on the ME platform surface for the detection of Bacillus anthracis spores. In response to the binding of spores to the phage on the ME biosensor, a corresponding decrease occurs in resonance frequency. Transmission electron microscopy (TEM) was used to verify the structure of phage under different combinations of salt/phage concentration. The chemistry of the phage solution alters phage bundling characteristics and, hence, influences both the sensitivity and detection limit of the ME biosensors. The frequency responses of the sensors were measured to determine the effects of salt concentration on the sensors' performance. Scanning electron microscopy (SEM) was used to confirm and quantify the binding of spores to the sensor surface. This showed that 420 mM salt at a phage concentration of 1 x 10(11) vir/mL results in an optimal distribution of immobilized phages on the sensor surface, consequently promoting better binding of spores to the biosensor's surface. Additionally, the sensors immobilized with phage under this condition were exposed to B. anthracis spores in different concentrations ranging from 5 x 10(1) to 5 x 10(8) cfu/mL in a flowing system. The results showed that the sensitivity of this ME biosensor was 202 Hz/decade.