This paper presents an investigation into magnetoelastic (ME) biosentinels that capture and detect low-concentration pathogenic bacteria in stagnant liquids. The ME biosentinels are designed to mimic a variety of white blood cell types, known as the main defensive mechanism in the human body against different pathogenic invaders. The ME biosentinels are composed of a freestanding ME resonator coated with an engineered phage that specifically binds with the pathogens of interest. These biosentinels are ferromagnetic and thus can be moved through a liquid by externally applied magnetic fields. In addition, when a time-varying magnetic field is applied, the ME biosentinels can be placed into mechanical resonance by magnetostriction. As soon as the biosentinels bind with the target pathogen through the phage-based biomolecular recognition, a change in the biosentinel’s resonant frequency occurs, and thereby the presence of the target pathogen can be detected. Detection of Bacillus anthracis spores under stagnant flow conditions was demonstrated.
This paper presents an investigation into the use of magnetoelastic biosensors for the rapid detection of Salmonella typhimurium on fresh spinach leaves. The biosensors used in this investigation were comprised of a strip-shaped, goldcoated
sensor platform (2 mm-long) diced from a ferromagnetic, amorphous alloy and a filamentous fd-tet phage which
specifically binds with S. typhimurium. After surface blocking with bovine serum albumin, these biosensors were,
without any preceding sample preparation, directly placed on wet spinach leaves inoculated with various concentrations
of S. typhimurium. Upon contact with cells, the phage binds S. typhimurium to the sensor thereby increasing the total
mass of the sensor. This change in mass causes a corresponding decrease in the sensor's resonant frequency. After 25
min, the sensors were collected from the leaf surface and measurements of the resonant frequency were performed
immediately. The total assay time was less than 30 min. The frequency changes for measurement sensors (i.e., phageimmobilized)
were found to be statistically different from those for control sensors (sensors without phage), down to 5 ×
106 cells/ml. The detection limit may be improved by using smaller, micron-sized sensors that will have a higher
probability of contacting Salmonella on the rough surfaces of spinach leaves.
This paper presents the direct detection of Salmonella typhimurium on shell eggs using a phage-based magnetoelastic
(ME) biosensor. The ME biosensor consists of a ME resonator as the sensor platform and E2 phage as the biorecognition
element that is genetically engineered to specifically bind with Salmonella typhimurium. The ME biosensor,
which is a wireless sensor, vibrates with a characteristic resonant frequency under an externally applied magnetic field.
Multiple sensors can easily be remotely monitored. Multiple measurement and control sensors were placed on the shell
eggs contaminated by Salmonella typhimurium solutions with different known concentrations. The resonant frequency of
sensors before and after the exposure to the spiked shell eggs was measured. The frequency shift of the measurement
sensors was significantly different than the control sensors indicating Salmonella contamination. Scanning electron
microscopy was used to confirm binding of Salmonella to the sensor surface and the resulting frequency shift results.
In this paper, we report a wireless magnetoelastic (ME) biosensor with phage as the bio-recognition probe for real time
detection of Salmonella typhimurium. The ME biosensor was constructed by immobilizing filamentous phage that
specifically binds with S. typhimurium onto the surface of a strip-shaped ME particle. The ME sensor oscillates with a
characteristic resonance frequency when subjected to a time varying magnetic field. Binding between the phage and
antigen (bacteria) causes a shift in the sensor's resonance frequency. Sensors with different dimensions were exposed to
various known concentrations of S. typhimurium ranging from 5 x101 to 5 x 108 cfu/ml. The detection limit of the ME
sensors was found to improve as the size of the sensor became smaller. The detection limit was found to improve from
161 Hz/decade (2mm length sensors) to 1150 Hz/decade (500 μm length sensors). The stability of the ME biosensor was
investigated by storing the sensor at different temperatures (25, 45, and 65 °C), and then evaluating the binding activity
of the stored biosensor after exposure to S. typhimurium solution (5 x 108 cfu/ml). The results showed that the phage-coated
biosensor is robust. Even after storage in excess of 60 days at 65 °C, the phage-coated sensors have a greater
binding affinity than the best antibody coated sensors stored for 1 day at 45 °C. The antibody coated sensors showed
near zero binding affinity after 3 days of storage at 65 °C.
We developed a high resolution light imaging system. Diffraction gratings with 100 nm width lines as well as less than
100 nm size features of different-shaped objects are clearly visible on a calibrated microscope test slide (Vainrub et al.,
Optics Letters, 2006, 31, 2855). The two-point resolution increase results from a known narrowing of the central
diffraction peak for the annular aperture. Better visibility and advanced contrast of the smallest features in the image are
due to enhancement of high spatial frequencies in the optical transfer function. The imaging system is portable, low
energy, and battery operated. It has been adapted to use in both transmitting and reflecting light. It is particularly
applicable for motile nanoform systems where structure and functions can be depicted in real time. We have isolated
micrometer and submicrometer particles, termed proteons, from human and animal blood. Proteons form by reversible
seeded aggregation of proteins around proteon nucleating centers (PNCs). PNCs are comprised of 1-2nm metallic
nanoclusters containing 40-300 atoms. Proteons are capable of spontaneous assembling into higher nanoform systems
assuming structure of complicated topology. The arrangement of complex proteon system mimics the structure of a
small biological cell. It has structures that imitate membrane and nucleolus or nuclei. Some of these nanoforms are
motile. They interact and divide. Complex nanoform systems can spontaneously reduce to simple proteons. The
physical properties of these nanoforms could shed some light on the properties of early life forms or forms at extreme
The Auburn University Detection and Food Safety Center has demonstrated real-time biosensor for the detection of Salmonella typimhurium, consisting of a thickness shear-mode (TSM) quartz resonator with antibodies immobilized in a Langmuir-Blodgett surface film. Scanning Electron Microscopy (SEM) images of bound Salmonella bacteria to both polished and unpolished TSM resonators were taken to correlate the mass of the bound organism to the Sauerbrey equation. Theoretical frequency shifts for unpolished TSM resonators predicted by the Sauerbrey equation are much smaller than experimentally measured frequency shift. The Salmonella detector operates in a liquid environment. The viscous properties of this liquid overlayer could influence the TSM resonator's response. Various liquid media were studied as a function of temperature (0 to 50 degree(s)C). The chicken exudate samples with varying fat content show coagulation occurring at temperatures above 35 degree(s)C. Kinematic viscosity test were performed with buffer solutions containing varying quantities of Salmonella bacteria. Since the TSM resonators only entrain a boundary layer of fluid near the surface, they do not respond to these background viscous property changes. Bilk viscosity increases when bacteria concentrations are high. This paper describes investigations of TSM resonator surface acoustic interactions - mass, fluid viscosity, and viscoelasticity - that affect the sensor.