This paper presents a portable magnetoelastic (ME) biosensor system that enables rapid, on-site detection of pathogenic bacteria. The system utilizes a patented portable resonant frequency analyzer and two 1 mm long ME biosensors (biosensors coated with and without phage binding a specific pathogen) enabling real-time measurement of resonant frequency changes. By comparing the response of the biosensors, the presence of the specific pathogen can be detected. In this work, detection of Salmonella Typhimurium cells was demonstrated, and it was found that down to 2,500 cfu can be detected in less than 10 min. The detection limit can be improved by using a smaller sensor (e.g., 500 um long sensors) and an optimal chamber design increasing the probability of bacterial cells striking the biosensor surface.
To perform rapid sensing of pathogens on the surface of food or food preparing plates, ME wireless biosensing system was combined with surface swab sampling techniques in this research. The ME biosensors which consist of ME resonators E2 phage was generally used for Salmonella typhimurium direct detections on the surfaces. E2 phage used in this research was designed for Salmonella typhimurium specific binding. Instead of measuring one spot at a time, the desired area or the whole area of a target surface can be swabbed for the inexpensive, rapid and easy-to-use pathogen collections. In this study, we first investigated the efficiency of capture and release of a model pathogen, Salmonella Typhimurium, by swab sampling on wet or dry surfaces. Plate counting was used to identify the recovery rates. The efficiency of capture and release was calculated and compared between various kinds of swabs which were composed of different tip materials, including cotton, rayon, and nylon-flocked ones.
Listeria monocytogenes is the major etiologic agent for foodborne Listeriosis in humans from consumption of readyto- eat (RTE) food. According to Center for Disease Control and Prevention, an estimated 1,600 people contract Listeriosis each year with approximately 260 deaths. This high rate of mortality has alerted the Food Safety Inspection and Services to release the Notice 23-99, Instructions for Verifying the L. monocytogenes Reassessment, on August 3, 1999 for their inspectors. According to the FDA’s Bacterial Analysis Manual Chapter 10, L. monocytogenes in RTE food samples is detected via microbiological culture-based tests, qPCR, pulsed-field gel electrophoresis, and other alternative methods. Unfortunately, these methods are time consuming (48-72 hours) and require dedicated laboratory facility. Thus, to develop a real-time L. monocytogenes biosensor, we isolated L. monocytogenes specific oligopeptides displayed on bacteriophages using modified biopanning procedures. In order to account for major temperature dependent morphological alterations of L. monocytogenes at 4°C versus 37°C, we used bacterial cells adapted to either temperature as the target in our biopanning. To date, we have isolated several candidate probes that can recognize either cold-adapted, warm-adapted L. monocytogenes cells, or both types of bacterial cells. Our isolated probes will be used on the magnetoelastic biosensor platforms for real-time detection of L. monocytogenes in RTE foods stored at 4°C or in samples/fluids for bacterium adapted to human body temperature.
In this paper, a novel device named as phage filter is designed and presented to capture and identify a small number of Salmonella Typhimurium cells from large volumes of water. This phage filter is constructed from a filter chamber, filter frames on a spindle, strip-shape magnetoelastic filter elements, and a spinning speed control unit. The filter elements are made from Metglas 2826MB and coated with a specifically designed phage that only binds with Salmonella Typhimurium. These phage-coated filter elements can be held and arranged on the filter frames by magnetic force produced from couples of permanent magnets in the frame. Layers of filter frames are fixed on the spindle. The spindle with filter frames and filter elements can spin in the filter chamber and the spinning speed can be continuously adjusted. When the filter works, the tested water passes through the filter frame, and Salmonella Typhimurium cells striking on the filter elements can be bound by the phage on the element surfaces and removed from the tested water.
Foodborne illness is a common public health problem because food can be contaminated with pathogens at any point in the farm-to-table continuum. This paper presents a method of capturing a quantity of a specific bacterial pathogen in a large volume of liquid using a biomolecular recognition filter. The filter consists of support frames made of a soft magnetic material and solenoid coils for magnetization/demagnetization of the frames. This filter is a planar, multi-layered arrangement of strip-shaped, phage-immobilized magnetoelastic (ME) biosensors that are magnetically held and arrayed on the filter frames. As a large volume of liquid passes through the biomolecular filter, the pathogen of interest is captured by the phage immobilized ME biosensors. This biomolecular filter is designed to capture a specific pathogen and allow non-specific debris to pass, thus avoiding a common clogging issue in conventional bead filters. In this work, single layer, double layers and triple layers of filter were test to capture Salmonella Typhimurium in a large volume of water. The effects of multiplication of filter layers on Salmonella capture efficiency will be discussed.
This paper investigates the accuracy of surface-scanning measurement of a wireless magnetoelastic (ME) biosensor for direct pathogen detection on solid surfaces. The model experiments were conducted on the surface of a at polyethylene (PE) plate. An ME biosensor (1 mm x 0.2 mm x 30 µm) was placed on the PE surface, and a surface-scanning detector was aligned to the sensor for wireless resonant frequency measurement. The position of the detector was accurately controlled by using a motorized three-axis translation system (i.e., controlled X, Y, and Z positions). The results showed that the resonant frequency variations of the sensor were -125 to +150 Hz for X and Y detector displacements of ± 600 µm and Z displacements of +100 to +500 µm. These resonant frequency variations were small compared to the sensor's initial resonant frequency (˂ 0.007% of 2.2 MHz initial resonant frequency) measured at the detector home position, indicating high accuracy of the measurement. In addition, the signal amplitude was, as anticipated, found to decrease exponentially with increasing detection distance (i.e., Z distance). Finally, additional experiments were conducted on the surface of cucumbers. Similar results were obtained.
This paper demonstrates a highly sensitive surface-scanning detector used for magnetoelastic (ME) biosensors for the detection of Salmonella on the surface of a polyethylene (PE) food preparation surface. The design and fabrication methods of the new planar spiral coil are introduced. Different concentrations of Salmonella were measured on the surface of a PE board. The efficacy of Salmonella capture and detection is discussed.
This paper investigates the effects of surface-scanning detector position on the resonant frequency and signal amplitude of a wireless magnetoelastic (ME) biosensor for direct pathogen detection on solid surfaces. The experiments were conducted on the surface of a flat polyethylene (PE) plate as a model study. An ME biosensor (1 mm × 0.2 mm × 30 μm) was placed on the PE surface, and a surface-scanning detector was brought close and aligned to the sensor for wireless resonant frequency measurement. The position of the detector was accurately controlled by using a motorized three-axis translation system (i.e., controlled X, Y, and Z positions). The results showed that the resonant frequency variations of the sensor were -125 to +150 Hz for X and Y detector displacements of ±600 μm and Z displacements of +100 to +500 μm. These resonant frequency variations were small compared to the sensor's initial resonant frequency (< 0.007% of 2.2 MHz initial resonant frequency) measured at the detector home position, indicating high accuracy of the measurement. In addition, the signal amplitude was, as anticipated, found to decrease exponentially with increasing detection distance (i.e., Z distance). Finally, additional experiments were conducted on the surface of cucumbers. Similar results were obtained.
This paper investigates a phage-based biomolecular filter that enables the evaluation of large volumes of liquids for the presence of small quantities of bacterial pathogens. The filter is a planar arrangement of phage-coated, strip-shaped magnetoelastic (ME) biosensors (4 mm × 0.8 mm × 0.03 mm), magnetically coupled to a filter frame structure, through which a liquid of interest flows. This "phage filter" is designed to capture specific bacterial pathogens and allow non-specific debris to pass, eliminating the common clogging issue in conventional bead filters. ANSYS Maxwell was used to simulate the magnetic field pattern required to hold ME biosensors densely and to optimize the frame design. Based on the simulation results, a phage filter structure was constructed, and a proof-in-concept experiment was conducted where a Salmonella solution of known concentration were passed through the filter, and the number of captured Salmonella was quantified by plate counting.
This paper presents a method for detection of a few pathogenic bacteria and determination of live versus dead cells. The method combines wireless phage-coated magnetoelastic (ME) biosensors and a surface-scanning dectector, enabling real-time monitoring of the growth of specific bacteria in a nutrient broth. The ME biosensor used in this investigation is composed of a strip-shaped ME resonator upon which an engineered bacteriophage is coated to capture a pathogen of interest. 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 1 in 105 background bacteria. The phage-coated ME biosensors were first exposed to a low-concentration Salmonella suspension to capture roughly 300 cells on the sensor surface. When the growth of Salmonella in the broth occurs, the mass of the biosensor increases, which results in a decrease in the biosensor's resonant frequency. Monitoring of this mass- induced resonant frequency change allows for real-time detection of the presence of Salmonella. Detection of a few bacteria is also possible by growing them to a sufficient number. The surface-scanning detector was used to measure resonant frequency changes of 25 biosensors sequentially in an automated manner as a function of time. This methodology offers direct, real-time detection, quantification, and viability determination of specific bacteria. The rate of the sensor's resonant frequency change was found to be largely dependent on the number of initially bound cells and the efficiency of cell growth.
This research project aims at establishing a computer platform especially for the analysis of process of laser welding. After the laser induced plasma photographs, metallographic photographs of the weld are scanned into computer and the welding parameters are input, the results of the analysis can be obtained by means of selecting different function-keys. The main results of analysis include: the solid angle of spatter distribution, the velocity of the unit volume spatter, the area of the weld, the penetration-to-width ratio of the weld, the included angle of side boundary line of the weld, the RGB chart and the grey isothermal chart of plasma and the area of laser welding plasma in the different temperature district and so on.
In this paper, the electron rotating radius and the corresponding length above surface of the workpiece where the electron density is notably reduced are calculated on the condition of adding magnetic field in laser welding according to the temperature of plasma and the average velocity of electron motion. The experiments results indicate that on the set condition, the weld area is increased by 18% with the weld penetration and the melting efficiency being increased by 22% and 13% respectively when the magnetic flux density added is set at 96 mT.
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