In this paper the performance of a magnetoelastic biosensor detection system for the simultaneous identification of B.
anthracis spores and S. typhimurium was investigated. This system was also designed for selective in-situ detection of
B. anthracis spores in the presence a mixed microbial population. The system was composed of a reference sensor
(devoid of phage), an E2 phage sensor (coated with phage specific to S. typhimurium) and a JRB7 phage sensor (coated
with phage specific to B. anthracis spores). When cells/spores are bound to the specific phage-based ME biosensor
surface, only the resonance frequency of the specific sensor changed. The instantaneous response of the multiple
sensor system was studied by exposing the system to B. anthracis spores and S. typhimurium suspensions sequentially.
A detection limit of 1.6×10<sup>3</sup> cfu/mL and 1.1×10<sup>3</sup> cfu/m was observed for JRB7 phage sensor and E2 phage sensor,
respectively. Additionally, the performance of the system was also evaluated by exposure to a flowing mixture of B.
anthracis spores (5×10<sup>1</sup>-5×10<sup>8</sup> cfu/ml) in the presence of B. cereus spores (5×10<sup>7</sup> cfu/ml). Only the JRB7 phage
biosensor responded to the B. anthracis spores. Moreover, there was no appreciable frequency change due to
non-specific binding when other microorganisms (spores) were in the mixture. A detection limit of 3×10<sup>2</sup> cfu/mL was
observed for JRB7 phage sensor. The results show that the multi-sensor detection system offers good performance,
including good sensitivity, selectivity and rapid detection.
In this paper, we report a wireless magnetoelastic (ME) biosensor with phage as the bio-recognition probe for real time
detection of <i>Salmonella typhimurium</i>. The ME biosensor was constructed by immobilizing filamentous phage that
specifically binds with <i>S. typhimurium</i> 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 <i>S. typhimurium</i> ranging from 5 x10<sup>1</sup> to 5 x 10<sup>8</sup> 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 <i>S. typhimurium</i> solution (5 x 10<sup>8</sup> 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.
Magnetoelastic sensors exhibit a characteristic resonance frequency upon the application of an alternating magnetic
field. In this research, magnetoelastic material was fabricated into micro-sized sensors coated with JRB7 phages to
specifically detect Bacillus anthracis spores. Research had shown that the sensor's resonant frequency decreases
linearly as its mass increases. As spores are captured, the mass increases. A high mass-sensitivity of up to 7.5 Hz/pg
allowed this sensor's use in applications requiring accurate sensing of a very low concentration of B. anthracis spores.
A B. anthracis spore weighs about 2 picograms. Two different sizes of sensors, 2000×400 μm and 1000×200 μm, were
used in this study. The resonant frequency and the sensitivity of the sensors were found to vary under different
magnitudes of DC biasing magnetic field. It was found that both the resonant frequency and the Q-value of the sensed
signal increase with an increase of the magnitude of the DC magnetic field until they approach magnetic saturation. As
the magnetic field was changed from low to high, it was observed that the signal amplitude increased to a maximum and
then decreased to undetectable. Finally, real-time detection of B. anthracis spores is performed under the optimum
magnetic field condition.
This article presents a contactless, remote sensing <i>Salmonella </i><i>typhimurium</i> sensor based on the principle of magnetostriction. Magnetostrictive materials have been used widely for various types of sensor systems. In this work, the use of a magnetostrictive material for the detection of Salmonella typhimurium has been established. The mass of the bacteria attached to the sensor causes changes in the resonance frequency of the sensor. Filamentous bacteriophage was used as a probe order to ensure specific and selective binding of the bacteria onto the sensor surface. Thus changes in response of the sensor due to the mass added onto the sensor caused by specific attachment of bacteria can be monitored in absence of any contact to the sensor. The response of the sensor due to increasing concentrations (from 5x10<sup>1</sup> to 5x10<sup>8</sup> cfu/ml) of the bacteria was studied. A reduction in the physical dimensions enhances the sensitivity of these sensors and hence different dimensions of the sensor ribbons were studied. For a <i>2mm</i> x <i>0.1mm </i>x <i>0.02mm </i>the detection limit was observed to be of the order of <i>10<sup>4</sup> </i><i>cfu/mL </i>and for a sensor of <i>1mm</i> x <i>0.2mm </i>x <i>0.02mm </i>a reduced detection limit of <i>10<sup>3</sup> cfu/mL </i>was achieved.
Magnetostrictive particles (MSPs) as biosensor platform have been developed recently. The principle of MSPs as sensor
platform is the same as that of other acoustic wave devices, such as quartz crystal microbalance. In this paper, the
fabrication, characterization and performance of phage-based MSP biosensors for detecting <i>Bacillus anthracis </i>spores
are reported. A commercially available magnetostrictive alloy was utilized to fabricate the sensor platform. The phage
was immobilized onto the MSPs using physical adsorption technology. The following performance of the phage-based
MSP sensors will be presented: sensitivity, response time, longevity, specificity and binding efficacy. The performance
of the sensors at static and dynamic conditions was characterized. The experimental results are confirmed by
microscopy photographs. The excellent performance including high sensitivity and rapid response is demonstrated.
More importantly, it is experimentally found that the phage-based MSP sensors have a much better longevity than
Novel mass-sensitive, magnetostrictive sensors have a characteristic resonant frequency that can be determined by monitoring the magnetic flux emitted by the sensor in response to an applied, time varying, magnetic field. This magnetostrictive platform has a unique advantage over conventional sensor platforms in that measurement is wireless or remote. These biosensors can thus be used in-situ for detecting pathogens and biological threat agents. In this work, we
have used a magnetostrictive platform immobilized with a polyclonal antibody (the bio-molecular recognition element) to form a biosensor for the detection of <i>Salmonella typhimurium</i>. Upon exposure to solutions containing <i>Salmonella typhimurium</i> bacteria, the bacteria were bound to the sensor and the additional mass of the bound bacteria caused a shift in the sensor's resonant frequency. Responses of the sensors to different concentrations of <i>S. typhimurium</i> were recorded and the results correlated with those obtained from scanning electron microscopy (SEM) images of samples.
Good agreement between the measured number of bound bacterial cells (attached mass) and frequency shifts were obtained. The longevity and specificity of the selected polyclonal antibody were also investigated and are reported.
Hydrazine is mostly used as a propellant in the control/propulsion system of missiles, spacecraft and satellites. However with its highly toxic and strong reducing nature, hydrazine is very dangerous to humans and the environment. In this research, a low cost, passive, and highly sensitive micro-sensor has been developed as an alarm device for real-time monitoring for the accidental release of hydrazine, and to insure the safety of personnel and the readiness of the system before lift-off. The micro-sensor is fabricated using standard microelectronic manufacturing techniques and is composed of interdigitated electrodes and a hydrazine-sensitive poly (3-hexylthiophene) (P3HT) thin film. When exposed to 1ppm of hydrazine gas, the compensation interaction between the reducing hydrazine gas and p-type doped P3HT leads to a five order magnitude increase in the resistance of the device. The sensor is capable of detecting hydrazine leaks from tens of ppb to tens of ppm concentration. The sensitivity of sensor increases with the increasing of hydrazine concentration and the decreasing of the polymer film thickness. A numerical simulation result based on the possible theoretical model is compared with the experimental data, which shows a good agreement.