Jiehui Wan

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 resonators 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 sensors 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.

Phage-Based Magnetoelastic Wireless Biosensors for Detecting Bacillus Anthracis Spores

A biosensor for the detection of biological warfare agents (Bacillus anthracis spores) was developed that combines the phage display technique with a magnetoelastic wireless detection platform. The affinity-based biosensor utilizes a phage-derived diagnostic probe as the biomolecular recognition element to capture target agents multivalently. Upon binding of the target agent to the sensor surface, the resonance frequency of the magnetoelastic biosensors decreases due to the additional mass of the target agent. Scanning electron microscopy was used to confirm binding of spores to the sensor surface. The sensitivity of the magnetoelastic acoustic sensor was tested to be 130 Hz per order of magnitude of spore concentration with a detection limit of 103 spores/ml. The specificity of the sensors was tested against spores of other closely related Bacillus species and a large preferential binding to Bacillus anthracis spores was observed. The longevity of the phage based biosensor was compared to traditional antibody based biosensors and found to exhibit a much longer life

Landscape phage-based magnetostrictive biosensor for detecting Bacillus anthracis spores

A new diagnostic probe selected from a landscape phage library was used in combination with a free standing magnetostrictive platform to form a wireless biosensor with quick response and high accuracy. The immobilization of the phage-derived probes leads to a 3D biomolecular recognition layer that captures the target spores multivalently. After the phage-coated biosensors were exposed to suspensions of the target spores, the binding of spores to the sensors resulted in a decrease of the resonant frequency due to the additional mass of the attached spores. Scanning electron microscopy was used to relate the observed frequency changes to the actual number of spores bound to the sensor

Detection of Salmonella typhimurium using phage-based magnetostrictive sensor

This article presents a contactless, remote sensing Salmonella typhimurium 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 5x101 to 5x108 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 2mm x 0.1mm x 0.02mm the detection limit was observed to be of the order of 104 cfu/mL and for a sensor of 1mm x 0.2mm x 0.02mm a reduced detection limit of 103 cfu/mL was achieved.

Phage-based magnetostrictive-acoustic microbiosensors for detecting bacillus anthracis spores

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 Bacillus anthracis 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 antibody-based sensors.

Hydrazine leak detection using poly (3-hexylthiophene) thin film micro-sensor

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.

Characterization of phage-coupled magnetoelastic micro-particles for the detection of Bacillus anthracis Sterne spores

A microfabricated magnetoelastic sensor immobilized with specific phage for the detection of Bacillus anthracis spores is presented. This micro-sensor can detect response signal remotely through magnetic field, enabling the in-situ measurement of target pathogens in aqueous environment. The sensors surface was modified by selected phage which provides the binding ability to B. anthracis spores. When exposed to B. anthracis spore solution, the resonant frequency of the sensor decreased due to the accumulated spore attachment on the surface. Sensors with dimensions of 200 times 40 times 4 mum were employed in the tests of increasing concentrations (102 to 108 cfu/ml) of B. anthracis spores. A detection limit of 102 cfu/ml, and a sensitivity of 13.1 kHz/decade, were observed. Scanning electron microscopy (SEM) photographs demonstrated binding of target analytes to biosensors compared to controls.

Detection of S. Typhimirium and Bacillus Anthracis Spores in a Flow System Using ME Biosensors by Optimizing Phage Chemistry

This paper presents the results of a study that investigates the optimization of phage chemistry during the fabrication of magnetoelastic (ME) biosensors for the detection of Salmonella typhimurium or Bacillus anthracis spores. The bundling characteristics of the phage filaments limit the ability of the biosensor to bind bacterial cells/spores. Experiments were performed to determine the proper phage concentration for the prevention of bundling in aqueous environments. Based on the transmission electron microscopy (TEM) and scanning electron microscopy (SEM) results, which verify the structure of phage under different concentrations and binding numbers of target species to the sensor surface, we found that phage concentrations of 1011 vir/ml exhibit the best sensor performance in terms of binding sensitivity. Additionally, the sensors immobilized with phage under this condition were tested in a flowing liquid system using S. typhimurium and B. anthracis spores suspensions in concentrations ranging from 5 times101 to 5 times 108 cfu/ml, separately. As cells/spores are bound to a ME biosensor surface, the additional mass of the spores causes a decrease in the resonance frequency of the sensor. The frequency response curves of the ME biosensors as a function of exposure time were then measured, and the detection limit of the ME biosensor was determined to be 5 times 103 cfu/ml.

Detection of Salmonella typhimurium using polyclonal antibody immobilized magnetostrictive biosensors

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 Salmonella typhimurium. Upon exposure to solutions containing Salmonella typhimurium bacteria, the bacteria were bound to the sensor and the additional mass of the bound bacteria caused a shift in the sensors resonant frequency. Responses of the sensors to different concentrations of S. typhimurium 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.

Characterization and Application of Wireless Magnetostrictive Micro-Sensors

Magnetostrictive materials have been investigated extensively for the application of physical, chemical and biological sensors recently. Higher precision and higher detection sensitivity requires microsensors or nanosensors to be used. In this research, the mass sensitivity and size effect of the free-standing magnetostrictive sensors is investigated down to the micro level both experimentally and theoretically. A highly efficient wireless signal query system is designed and employed. The procedure of the fabrication of micro-sized sensors is investigated to ensure optimum sensor surface for immobilization and excellent frequency signals. The damping effect in liquid is tested and the high Q factor promises potential application in chemical and biological areas. A numerical approach is also used for sensor modeling and related to experimental results