Magnetoelastic Research Articles

Характеристики локализации волновой энергии около неровных поверхностей пьезоэлектрического волновода.

Propagation of high-frequency electro-elastic normal wave signal in a composite waveguide is investigated. The composite waveguide consists of a base piezoelectric layer with rough surfaces, which respectively are filled with an ideal conductor and ideal dielectric. The problem is solved by the method of virtual cross sections and input of Magneto Elastic Layered Systems (MELS) hypotheses. The influence of surfaces roughness, as well as and the influence of surface smoothness (the effects of different physical and mechanical boundary conditions) on the process of propagation of high frequency electro-elastic normal wave signal is discussed. The behaviors of wave amplitude and frequency characteristics in the composite waveguide are numerically investigated at the propagation of normal wave signal. It is shown that if the surface roughness of the piezoelectric layer is not filled, only one shortwave mode occurs. The filling of the surface roughness with dielectric and conductor, leads to the appearance of up to four such wave modes, depending on the length of the wave signal. The dispersion dependencies for all possible characteristic modes of shear elastic waves are given. It is shown that on the propagation of slow waves, occurs frequency zone of silence at certain wave lengths.

Decision Wave Equation and Block Diagram of Electro Magneto Elastic Actuator Nano - and Micro Displacement for Communications Systems

Decision wave equation, structural - parametric model and block diagram of electro magneto elastic actuators are obtained, its transfer functions are bult. Effects of geometric and physical parameters of electro magneto elastic actuators and external load on its dynamic characteristics are determined. For calculation of communications systems with piezoactuators the block diagram and the transfer functions of piezoactuators are obtained.

Thermal Stability of Phage Peptide Probes Vs. Aptamer for Salmonella Detection on Magnetoelastic Biosensors Platform

According to CDC, Salmonella enterica spp. is one of the major food pathogens commonly associated with outbreaks in United States. A rapid sensor test for Salmonella detection is essential to improve and monitor food safety procedures. Magnetoelastic (ME) sensors have been recently developed as a novel, real-time, and wireless platform for Salmonella typhimurum detection in food systems (Horikawa et al., 2015). The sizes of the ME sensors are only a few millimeters or less, and are freestanding ME resonators that are very cost efficient after microfabrication. The performance of this ME biosensor relies on the adhesion characteristics of the bio-recognition probes coating on the sensor surface through Au deposition, and they also rely on the probe’s binding affinity to bacterial targets for low Salmonella detection. When a time-varying magnetic field is applied, the ME biosensors can be placed into mechanical resonance by magnetostriction. Upon the attachment of the target pathogen to the bio-recognition probes on the sensor, a resonant frequency shift of this sensor occurs to give a positive detection signal. Therefore, a good affinity and stable bio-recognition probe is essential for this ME biosensor platform. Environmental monitoring, such as monitoring food pathogens in poultry processing plant with heat and humidity requires thermostable probes. A thermal stable probe can maintain its sensitivity and specificity to the target pathogens when the environment temperature is not favored. Antibodies, phage peptides, and aptamers (DNA/RNA) are three major groups of bio-recognition molecules currently used in the pathogen detection fields. Even though antibodies are known to bind to bacteria targets with good affinity and specificity, antibody-based assays have several environmental limitations, including not holding their structures under high temperature conditions. Phage peptides are engineered and developed through a process called biopanning selection using phage display methods. After selecting the good affinity phage peptide to its target, the whole phage with this peptide can be used directly on the sensor platform. These phages, called filamentous phages, are known to survive in hard environments, like high temperatures. Petrenko et al, (2005) reported that phage-derived probes bind to biological agents and generate detectable signals at the temperatures of 63°C. Aptamers are short synthetic molecules that can comprise of nucleic or amino acid (DNA in this study) and commonly selected through SELEX procedures (Systematic Evolution of Ligands by Exponential Enrichment). There are studies showed that aptamers are more effective than antibodies for target binding at higher temperatures. However, there is no study comparing the affinity of phages vs. aptamers to a target pathogen in various thermo-conditions. In this study, the affinity of phage probes vs. aptamers to Salmonella enterica Typhimurium at various thermal conditions was evaluated using ELISA (Enzyme Link Immunosorbent Assay) tests. DNA aptamers were able to perform Salmonella detection at 50⁰C. When the temperature was increased to 60⁰C, the aptamers’ detection signals dropped down to baseline. Phage probes showed good thermal stabilities for Salmonella detection when the temperature was increased to 60⁰C. To our knowledge, this is the first report of a comparison study of phages vs aptamers used for pathogen detection.

The Bathtub Method for Detecting Small Quantities of Specific Pathogens

Current techniques used to concentrate pathogens, such as centrifugation and size-exclusion filtration, are non-specific for pathogens of interest and inefficient to deal with large volumes of liquids and liquid foods. In addition, the isolated pathogens need to be analyzed subsequently with expensive, laborious, sample-based lab methods (e.g., culturing and PCR) that do not enable rapid identification of the pathogens. This paper presents a revolutionary method for the capture and rapid detection of small amounts of specific bacteria from entire liquid streams. The method combines a volumetric biomolecular filter and an automated biosensor measurement system. The volumetric biomolecular filter is a three-dimensional, multi-layered net with each layer made up of hundreds of phage-coated magnetoelastic (ME) biosensors with a pre-determined resonant frequency. These biosensors are arrayed with a desired spacing and held flexibly (i.e., cantilever-like configuration) on an electro-magnetized silicon steel comb structure. The phage that is coated on the biosensors are responsible for capturing a specific pathogen. In this way, only the pathogen of interest can be captured on the filter whereas the other matters (non-specific pathogens, debris, etc.) are allowed to pass. In addition, the biosensors can bend over for large, heavy debris, eliminating a common issue of clogging found in the current filtration techniques. Once the entire liquid is flowed over, the biosensors on the filter are transferred into etched cavities on a silicon wafer by shutting off the electromagnetic field. These etched cavities are indexed such that a surface-scanning detector can be used to wirelessly measure the biosensors sequentially in an automated manner. The resonant frequency changes of the biosensors due to the attachment of the pathogen can be measured in 250 milliseconds per sensor. The presented method enables the evaluation of large volumes of liquids for the presence of small numbers of pathogens. The capture efficiency of pathogens was found to be dependent on the filter design.

Thermal Stability of Phage Peptide Probes Vs. Aptamer for Salmonella Detection on Magnetoelastic Biosensors Platform

Rapid and reliable detections for foodborne pathogens are essential to monitor food and improve food safety procedures. Food monitoring, such as monitoring contaminated foods in poultry processing plants and/or field farms with high heat environments, requires thermostable bio-probes on the sensor surfaces for accurate detections. Phage based magnetoelastic (ME) biosensors have been recently developed as a real-time and wireless platform for Salmonella enterica serotype Typhimurum detection in various food systems. The thermostability of phage and aptamer probes were studied here and their binding to Salmonella Typhimurium cells were evaluated using enzyme-linked immunosorbent assay (ELISA) format at various temperatures. The ELISA format can be used to mimic the probe immobilization conditions on ME sensor surfaces and can test bio-probes’ performance without the variability that arises from different ME sensor lots. The results of this study can be further applied in the development of the ME biosensor platform.

The Bathtub Method for Detecting Small Quantities of Specific Pathogens

This paper presents a rapid method for detecting small quantities of specific bacteria. The method combines phage-coated magnetoelastic (ME) biosensors, microfabricated arrayed bathtubs for cell culture, a surface-scanning detector, and a motorized translation system, enabling real-time monitoring of the growth of specific bacteria in a nutrient broth. Rapid detectionof a few bacterial cells is possible, depending on the sensor size and efficiency of bacterial growth.

Bacterial assessment of phage magnetoelastic sensors for Salmonella enterica Typhimurium detection in chicken meat

Salmonella is one of the most common pathogens associated with foodborne illness in chickens. Food outbreaks from this pathogen haven’t declined in the past 15 years according to the data from Centers for Disease Control and Prevention. It is our goal to improve food safety monitoring in this area by developing a real time Salmonella detection sensor on food surfaces. Previously, we demonstrated the use of phage C4-22 immobilized onto a rapid magnetoelastic (ME) biosensor for use as a front-line detection ligand to detect all Salmonella enterica serotypes in Tris Buffer Saline (TBS). In this study, by using fluorescent imaging, the phage peptide binding to Salmonella enterica serotype Typhimurium cells is again confirmed. Moreover, we constructed two detection models to evaluate the detection of Salmonella on/in chicken meat using the phage coated ME sensors.In the chicken surface detection method, phage C4-22 sensors demonstrated more than 12 times higher Salmonella binding capacity than the control sensors with no phage for the Salmonella spiked at the concentration of 7.86 × 105 cfu/mm2. In the second model, phage sensors were placed at different depths inside the chicken breast (0.1 cm; 0.5 cm; 1.0 cm below the meat surface) after surface inoculation of Salmonella. The second detection system showed that 23.27%–33% of the inoculated Salmonella cells absorbed inside the chicken breast fillets below 0.1 cm of the surface.The data for direct detection on chicken showed that phage C4-22 ME biosensors bind ultimately when there are high concentrations of Salmonella on the chicken surface. The results also suggest that the phage sensors can detect Salmonella effectively when the bacterial contaminants are absorbed into the chicken, and are not detectable by the surface detection method.

Phage‐Based Biosensor and Optimization of Surface Blocking Agents to Detect Salmonella Typhimurium on Romaine Lettuce

AbstractThe development of rapid detection technologies in parallel with understanding production practices will markedly improve the microbiological safety of leafy vegetables. The objective of this study was on the application of phage‐based magnetoelastic (ME) biosensors and optimization of selected surface blocking agents for a rapid detection for Salmonella Typhimurium on Romaine lettuce. Initially, Romaine lettuce hearts surface was examined for structural differences followed by attachment and distribution of S. Typhimurium using scanning electron microscopy (SEM). Furthermore, selected surface blocking agents were compared and optimized for the application of phage‐based ME biosensors surface. A total of 156 observations, ranging from 1 to 8 logs CFU/ml, and 18 frequency measurements were recorded and analyzed. Both measurement (with E2 phage) and control (without E2 phage) sensors were blocked with selected blocking agents to prevent nonspecific binding. Statistical analysis using ANOVA revealed that there was a significant difference between controls and measurements (P < 0.001). The comparison showed that 5 × 102 CFU/mL and higher concentrations of S. Typhimurium were detected on Romaine lettuce surface, and PEG performed better as a blocking agent of choice. Understanding the complexity of the bacteria‐plant surface interaction and improved detection protocol will provide a solid foundation to design feasible control strategies.Practical ApplicationsSalmonella species are generally associated with food products of animal origin and recently leafy green vegetables have been considered as a major public health concern and source of the bacteria. There is still a need to explore swift and reliable detection protocol, which could be easily applied to leafy vegetables from the farm to consumer. In this study, we have demonstrated the rapid detection for Salmonella Typhimurium on Romaine lettuce using phage‐based protocol. Furthermore, better surface blocking agent was optimized for the protocol. Further optimization of phage‐based detection approach could be instrumental to develop better Salmonella detection approach that can be adopted and used from farms to the consumer level.

The efficiency of application of virtual cross-sections method and hypotheses MELS in problems of wave signal propagation in elastic waveguides with rough surfaces

The efficiency of virtual cross sections method and MELS (Magneto Elastic Layered Systems) hypotheses application is shown on model problem about distribution of wave field in thin surface layers of waveguide when plane wave signal is propagating in it. The impact of surface non-smoothness on characteristics of propagation of high-frequency horizontally polarized wave signal in isotropic elastic half-space is studied. It is shown that the non-smoothness leads to strong distortion of the wave signal over the waveguide thickness and along wave signal propagation direction as well. Â Numerical comparative analysis of change in amplitude and phase characteristics of obtained wave fields against roughness of weakly inhomogeneous surface of homogeneous elastic half-space surface is done by classical method and by proposed approach for different kind of non-smoothness.

Rapid Detection of Pathogens By a 3D Biomolecular Filter and Automated Biosensor Measurement System for Liquid

A new method of rapid detection of pathogens by 3D biomolecular filtering and automated indexing plate measurement has been demonstrated. In this process, a liquid containing pathogens is passed through a 3D biomolecular filter composed of planar arrays of MagnetoElastic (ME) biosensors held by a magnetic field. This filter captures specific target pathogens (in our demonstration case, Salmonella) in the liquid as it passes over the filter. The experiment will be under different Salmonella concentrations, different flowing rate, different number of ME biosensors and different solution volume. Capture of the pathogens is by specific biomolecular recognition, not size exclusion as with traditional filters. After the entire liquid has passed over the filter, the magnetic field is shut off and the individual biosensors collected and dried. The biosensors are then placed on an indexing plate consisting of an array of rectangular cavities approximately 10% larger in size than the ME biosensors. A vibrating table is used to vibrate the ME biosensors into motion until each cavity of the plate is occupied by a single ME biosensor. The biosensors are then measured by sequentially positioning the sensors under a surface scanning detection coil for measurement of the final resonance frequency of the biosensors using an automated translation system. In this manner, a single sensor can be measured in less than 2 seconds with 1000 sensors being measured in less than 30 minutes.

Rapid Detection of Live Versus Dead Bacteria

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.

Double-Layer Planar Coil Detector for Improved Detection of Salmonella on Food Contact Surfaces

This paper presents an investigation into improved, direct Salmonella detection on food contact surfaces using a double-layer planar coil detector and wireless phage-based magnetoelastic (ME) biosensors. Comparing with the single-layer coil detectors used in our previous research, double-layer coils with appropriate designs allow for better magnetic excitation of the biosensor and sensitivity of detection. In this way, a longer stand-off distance (distance between the sensor and detector), which may be necessary for testing surfaces with large roughness and curvatures, can be achieved. In addition, smaller biosensors (e.g., sub-millimeter long) with higher mass sensitivity can also be measured with this sensitive double-layer coil detector. Standard microelectronic fabrication techniques (photolithography, electroplating, etching and sputtering) were used to fabricate double-layer coils with various design parameters, including the thickness of layers, width, height, and spacing of coil turns. Both theoretical calculations and experimental data showed that the above coil geometric parameters have large effects on the signal amplitude, stand-off distance and detection sensitivity. Finally, with the newly fabricated double-layer coil detector, detection of Salmonella on a food-grade, ultra-high-molecular-weight polyethylene (UHMW-PE) surface was demonstrated. Multiple biosensors were measured simultaneously with a longer detection distance (> 1 mm). This double-layer scanning coil detector therefore facilitates the detection of pathogens on food and food contact surfaces.

Detection system based on magnetoelastic sensor for classical swine fever virus

In this paper, a magnetoelastic (ME) sensing system for the detection of classical swine fever virus (CSFV) is presented. The detection system comprises a test paper and a measurement circuit. The test paper consists mainly of an ME biosensor to detect the CSFV. Based on the impedance analysis technique, the measurement circuit is designed to measure the resonance frequency of the ME biosensor. The anti-CSFV IgG is immobilized onto the ME sensor surface to form the ME biosensor through a physical absorption approach. The experimental results show that the shift in the resonance frequency of the ME biosensor increases with the augmentation of the CSFV concentration. The effectiveness of the combination between the anti-CSFV IgG and CSFV is confirmed by the scanning electron microscopy (SEM) images, the sandwich-based enzyme-linked immunosorbent assay (ELISA) analysis, the interference study and the reference biosensor test method. The resonance frequency shift is linearly proportional to the concentration in the range from 0 to 2.5μg/ml, and becomes sub-linear at higher concentrations. The ME biosensor for CSFV detection has a sensitivity of about 95Hz/μg·ml−1, with a detection limit of 0.6μg/ml.

Large magnetic anisotropy enhancement in size controlled Ni nanowires electrodeposited into nanoporous alumina templates

A large enhancement of the magnetic anisotropy of Ni nanowires (NWs) embedded in anodic aluminium oxide porous membranes is obtained as a result of an induced magnetoelastic (ME) anisotropy contribution. This unusual large anisotropy enhancement depends on the diameter of the NWs and exceeds the magnetostatic (MS) contribution. As a consequence, it leads to effective magnetic anisotropy energies as large as erg cm−3, which are of the same order of magnitude and comparable to the MS energies of harder magnetic materials like Co NWs. Specifically, from ferromagnetic resonance experiments, the magnetic anisotropy of the NWs has been observed to increase as its diameter is decreased, leading to values that are about four times larger than the corresponding value when only the MS anisotropy is present. Our results are consistent with the recently proposed growth mechanism of Ni NWs that proceeds via a poly-crystalline stage at the bottom followed by a single-crystalline stage with texture [110] parallel to the axis of the NWs. A strong correlation between reducing the diameter of the NWs with the decrease of the length of the poly-crystalline segment and the enhancement of the effective magnetic anisotropy has been shown. Magnetization curves obtained from alternating gradient magnetometry experiments show that the average ME anisotropy results from the competition between the magnetic anisotropies of both crystalline segments of the NWs. Understanding the influence of size and confinement effects on the magnetic properties of nanocomposites is of prime interest for the development of novel and agile devices.

Rapid and Sensitive Detection of Salmonella Typhimurium on Plastic Food Processing Plates by Using Wireless Biosensors

Food products can be contaminated with bacteria, spores, and other pathogens at any point in the farm-to-table continuum. This paper presents an investigation into rapid, sensitive detection of Salmonella Typhimurium on plastic food processing plates by using wireless magnetoelastic (ME) biosensors. In this research, a planar spiral coil was microfabricated and employed as a surface-scanning detector for real-time, in-situ measurement of the biosensors without sample preparation and/or enrichment in the testing process. The ME biosensor consists of an ME resonator, made from metallic glass (Metglas alloy 2826MB), as the signal transducer and E2 phage as the bio-molecular recognition element that is engineered to selectively bind with Salmonella Typhimurium. Both measurement sensors (multiple E2 phage-coated biosensors) and control sensors (multiple biosensors without phage) were prepared and distributed on a food grade plastic plate contaminated with Salmonella Typhimurium with known volumes and concentrations. The resonant frequency changes of the measurement sensors due to specific binding of Salmonella Typhimurium were found to be statistically different from those of the control sensors.

Direct Detection of Salmonella on Fresh Produce

This paper presents a method of bacterial detection that directly detects and quantifies the presence of specific bacteria on the surfaces of fresh produce without sample preparation (water rinse, soak, stomaching, etc.) and/or enrichment. The method combines wireless magnetoelastic (ME) biosensors and a surface-scanning detector for the swift screening of foods. Tests were conducted on tomatoes spiked with difference concentrations of Salmonella Typhimurium as a model pathogen. The speed of detection was from 2 to 10 minutes with a limit of detection (LOD) in a range of 102 to 104 cfu/mm2. The current LOD can be improved by using smaller, more sensitive ME biosensors (sub-millimeters in length) with an appropriate quantity. The presented method can be used on site for food inspection and outbreak investigation.

Homogenization and multiscale stability analysis in finite magneto-electro-elasticity. Application to soft matter EE, ME and MEE composites

Soft matter electro-elastic (EE), magneto-elastic (ME) and magneto-electro-elastic (MEE) composites exhibit coupled material behavior at large strains. Examples are electro-active polymers and magneto-rheological elastomers, which respond by a deformation to applied electric or magnetic fields, and are used in advanced industrial environments as sensors and actuators. Polymer-based magneto-electric-elastic composites are a new class of tailor-made materials with promising future applications. Here, a magneto-electric coupling effect is achieved as a homogenized macro-response of the composite with electro-active and magneto-active constituents. These soft composite materials show different types of instability phenomena, which even might be exploited for future enhancement of their performance. This covers micro-structural instabilities, such as buckling of micro-fibers or particles, as well as material instabilities in the form of limit-points in the local constitutive response. Here, the homogenization-based scale bridging links long wavelength micro-structural instabilities to material instabilities at the macro-scale. This work outlines a comprehensive framework of an energy-based computational homogenization in electro-magneto-mechanics, which allows a tracking of postcritical solution paths such as those related to pull-in instabilities. It provides variational-based definitions of multiscale structural and material stability phenomena. The starting point is a minimization principle of averaged electro-magneto-elastic energy, that is discretized by using electric and magnetic vector potentials. Next, computationally more effective representations based on scalar potentials are considered by a reformulation of the energy in terms of an averaged enthalpy functional. Structural stability is analyzed based on perturbations of the averaged energy, while local material stability is defined by a generalized quasi-convexity condition. It is shown that the incremental arrays which govern the stability criteria appear within the convenient enthalpy-based representation in a distinct diagonal form, containing mechanical and electro-magnetic partitions. Representative simulations demonstrate a tracking of inhomogeneous EE, ME and MEE composites, showing the development of postcritical zones in the microstructure and a possible unstable homogenized material response.

Real-Time Detection of Salmonella on Fresh Apples Using Magnetoelastic Biosensors Operating Under Multi-Harmonic Resonance Modes

This paper investigates real-time detection of Salmonella on fresh apples using phage-coated magnetoelastic (ME) biosensors that operate under multi-harmonic resonance modes. The ME biosensor is a class of mass-sensitive biosensors that is being developed for rapid, on-site pathogen detection in the food system. The ME biosensor used in this work consists of a freestanding, strip-shaped ME resonator (1 mm x 0.2 mm x 30 um) as the signal transducer and E2-phage that specifically binds with the pathogen of interest. The ME resonator is made of an amorphous, ferromagnetic alloy with magnetostrictive properties and hence can be placed into mechanical resonance by an externally applied time-varying magnetic field. When this phage-coated ME biosensor comes into contact and binds specifically with the target pathogen, the mass of the biosensor increases, resulting in a decrease in the biosensor's resonant frequency. The conventional theory describes that the mass sensitivity of the ME biosensor (i.e., the ratio of the resonant frequency change to the mass change) is proportional to the harmonic, n, defined as an integer multiple of the fundamental resonant frequency (n = 1, 2, 3, ···). Hence, improved mass sensitivity can be obtained by measuring resonant frequency changes of higher harmonic modes. Additionally, measuring and analyzing multi-harmonic resonant frequencies can reduce possible false negative detection resulting from the Salmonella that are attached to the nodes of the vibrating sensors. As a proof-in-concept experiment, in-situ Salmonella detection on fresh apples was conducted. Both measurement (with phage) and control (without phage) sensors were prepared and placed directly on apples spiked with Salmonella. The sensors’ resonant frequency shifts were then measured in situ using a surface-scanning coil detector as a function of time. While the resonant frequency shifts of the control sensors remained negligible, those of the measurement sensors decreased largely as time progressed, indicating that specific binding of the Salmonella on the measurement sensors had occurred. In addition, the mass sensitivity was found to improve for higher harmonic modes (the 2nd and 3rd longitudinal modes) compared to the fundamental mode. False negative detection was also reduced, which was confirmed by inspecting the sensor surface using SEM and comparing the number of bound Salmonella to the measured frequency shift data. Hence, enhanced detection of Salmonella has been demonstrated using ME biosensors operating in multi-harmonic resonance modes.

Oligopeptide Probe Coated Magnetoelastic Biosensors for the Rapid Detection of Salmonella Typhimurium

Magnetoelastic (ME) biosensors are composed of a resonating platform upon which molecular recognition probes are coated to capture and bind with a target species. Previously, we developed methods to isolate highly selective phage-displayed oligopeptide probes and immobilize them upon ME sensor platforms. These methods were used to isolate highly selective Salmonella enterica serovar Typhimurium probes that do not bind to other serovars of pathogenic Salmonella. The probes were tagged with Strep II tag before affinity immobilization upon a streptavidin coated ME sensor platform. The limits of detection were determined by testing over the range of 102 to 106 cells and these ME biosensors were found to have greater sensitivity than other ME biosensors coated with E2 phage. The ME biosensors coated with oligopeptide probes were found to be highly selective for S. Typhimurium and did not react with S. Enteritidis, S. Newport, or E. coli O157:H7. These results demonstrate the efficacy of the ME biosensor method to detect S. Typhimurium and validate our approach to improve the sensitivity and selectivity of the sensor. The techniques developed in this work can be easily adapted for any foodborne or other agriculturally important bacterial pathogens.

Pulse Excitation Method for Magnetoelastic Biosensors

Magnetoelastic (ME) biosensors are being investigated to detect and monitor the presence of foodborne pathogens that may contaminate our foods between the farm and the table. ME biosensors are based upon free-standing, vibrating platforms that change their resonant frequency in response to the capture and accumulation of target pathogens upon the sensor surfaces. The sensor platform is caused to vibrate by an external magnetic excitation field. A common excitation method is to sweep the magnetic field across a range of frequencies that are expected to include the resonant frequency of the sensor. This requires that one know beforehand the resonant frequency and the anticipated frequency shift caused by the capture of the target species, or search for these during measurement. In this work, an alternative (pulse) excitation method has been investigated to measure the resonant frequency of ME biosensors. A pulsed magnetic field was used to excite ME sensors to vibrate with a damped oscillation that decays rapidly. The resonant frequency is determined from the sensor response to the pulse excitation. The performance of a system designed to excite and measure the resonant frequencies of ME biosensors is described and its performance characterized. The operation of the system is demonstrated through the detection of Salmonella on fresh produce.