Pathogen Detection Using Magnetoelastic Biosentinels - Biomedical Engineering Systems and Technologies - page 48

Fig. 1. Bio-inspired sentinels will target different types of bacteria ( E. coli, Salmonella Typhi-
murium, etc.) mimicking white blood cells that target different invasive pathogens [1]

2 Theory of the Biosentinel

A biosentinel is constructed of a freestanding magnetoelastic (ME) resonator (trans-
ducer platform) that is coated with a biorecognition layer (e.g. antibodies or bacterio-
phage) that specifically captures or binds a single type of pathogen. The resonator is
constructed from an iron-based, amorphous alloy with magnetostrictive properties.
Magnetostrictive materials undergo a change in shape when subjected to an applied
magnetic field. If the magnetic field is aligned along the length direction of the reso-
nator and varied at the proper frequency, the structure can achieve resonance. The
detection principle of the ME sentinels is shown in Figure 2. The freestanding ME
resonator serves as the transduction platform, actuated into resonance by the applica-
tion of an alternating magnetic field. Upon contact with the specific target bacteria,
the biorecognition element on the biosentinel's surface captures the target bacterial
cells, causing the overall sensor mass to increase which results in a decrease in the
resonant frequency. The resonant frequency is remotely and wirelessly measured
using a pick-up coil. No onboard power is required by a biosentinel; instead, electro-
magnetic energy is harvested from the surroundings.

Pick-Up Coil

Driving Coil

Result

Biorecognition Layer
Target
Pathogens

Apply Varying
Magnetic Field

ME Biosentinel
Resulting Field

Magnetoelastic Platform
nm to µm sized resonator

Fig. 2. Detection principle of ME biosentinel. A modulated magnetic field causes the sentinel
to resonate. Binding of target bacteria to the sentinel causes the resonant frequency to decrease.