Bryan A. Chin

Rapid and sensitive biosensor for Salmonella

The rapid and sensitive detection of Salmonella typhymurium based on the use of a polyclonal antibody immobilized by the Langmuir-Blodgett method on the surface of a quartz crystal acoustic wave device was demonstrated. The binding of bacteria to the surface changed the crystal resonance parameters; these were quantified by the output voltage of the sensor instrumentation. The sensor had a lower detection limit of a few hundred cells/ml, and a response time of < 100 s over the range of 10(2)-10(10) cells/ml. The sensor response was linear between bacterial concentrations of 10(2)-10(7) cells/ml, with a sensitivity of 18 mV/decade. The binding of bacteria was specific with two binding sites needed to bind a single cell. The sensors preserve approximately 75% of their sensitivity over a period of 32 days.

Direct detection of Salmonella typhimurium on fresh produce using phage-based magnetoelastic biosensors.

Current bacterial detection methods require the collection of samples followed by preparation and analysis in the laboratory, both time and labour consuming steps. More importantly, because of cost, only a limited number of samples can be taken and analyzed. This paper presents the results of an investigation to directly detect Salmonella typhimurium on fresh tomato surfaces using phage-based magnetoelastic (ME) biosensors. The biosensor is composed of a ME resonator platform coated with filamentous E2 phage, engineered to bind with S. typhimurium. The ME biosensors are wireless sensors, whose resonance oscillation and resonance frequency are actuated and detected through magnetic fields. The sensors used in this study were 0.028 mm×0.2 mm×1 mm in size. In this study, the tomato surface was spiked with S. typhimurium suspensions with concentrations ranging from 5×10(1) to 5×10(8)CFU/ml and then allowed to dry in air. The detection was conducted by directly placing ME measurement biosensors and control sensors on the spiked surface for 30 min in a humid environment. The control sensors were identical to the measurement biosensors, but without phage. Both measurement and control sensors were blocked with BSA to reduce non-specific binding. The resonance frequencies of both measurement and control sensors were measured prior to and after the placement of the sensors on the tomato. Shifts in the resonance frequency of the measurement biosensors were observed, while the control sensors showed negligible change. Scanning electron microscopy (SEM) was used to verify the specific binding of S. typhimurium to the biosensor. Results of multiple biosensor detection and corresponding analyzes showed statistically different responses between the measurement and control sensors for tomatoes spiked with S. typhimurium suspensions with concentrations of 5×10(2)CFU/ml and greater. This study demonstrates the direct detection of food-borne bacteria on fresh produce.

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.

Infrared sensing techniques for penetration depth control of the submerged arc welding process

Abstract This paper presents an investigation into the development of a rugged, low cost, point infrared sensor to monitor and control the welding process in harsh fabrication environments. Perturbations occurring during the welding process create changes in the temperature distributions of the plates being welded. By monitoring the changes in these temperature distributions, action can be implemented to eliminate or mitigate defects that may form due to the process perturbations. Heat transfer analyses were performed to study the effects of disturbances to the welding process on the surface temperature of the plates being welded. A point sensor was used to monitor changes in the plate surface temperatures occurring during the welding process. The objective was to demonstrate that weld bead penetration depth could be monitored and controlled during both gas tungsten arc welding (GTAW) and submerged arc welding (SAW) processes to eliminate or reduce weld defects. The infrared energy exchange between a defined area on the topside plate surface and the sensor was monitored during the welding process and compared to predictions of the heat transfer analyses. Changes in the plate geometry (gap size, plate thickness, and cooling sinks representing stiffeners) were introduced during the experiments to perturb the welding process. Using the infrared sensor, constant depth of penetration was maintained in the presence of these perturbations by feedback control of the welding process parameters.

Specific and selective biosensor for Salmonella and its detection in the environment

The specific and selective detection of Salmonella typhymurium based on the use of a polyclonal antibody immobilized by the Langmuir-Blodgett method on the surface of a quartz crystal acoustic wave device was demonstrated in liquid samples. These biosensors were selective to S. typhymurium in the presence of large concentrations of Escherichia coli O157:H7. They were also specific to S. typhymurium since bacteria preincubated with free antibody produced no signal. Dark-field and electron microscopy showed that two different antibodies, polyvalent somatic O and flagellar H7, were immobilized on the sensor surface producing two distinct attachments of bacteria at the liquid-solid interface. The somatic O antibody exhibits a rigid, binding, while the flagellar H7 antibody forms a flexible connection allowing a large degree of freedom. When the attachment of bacteria was rigid and strong, the responses of the acoustic wave sensors correlated with changes in the mass of bacteria present at the liquid-solid interface. In contrast, when attachment was flexible, the sensor signals were inversely proportional to the additional mass of bound bacteria. This difference is probably determined by the interfacial viscoelasticity and by acoustic and electromagnetic coupling. The signals of environmentally aged sensors with either predominantly rigid or flexible positioning of bacteria were correlated with changes in mass at the liquid-solid interface. Sensors with O or H type of binding could be used for analytical purposes.

Control of the welding process using infrared sensors

Integration of sensors in a welding system enhances the quality of the welds produced. Variations in three welding process parameters-weld bead width, penetration depth, and torch position-were monitored using an infrared sensor. Intentionally induced variations in each of these welding parameters were found to affect uniquely the plate surface temperature distributions measured by the infrared sensor. The effects of weld bead width and torch position perturbations on the temperature distribution were separated so as to identify and control these two weld process parameters simultaneously. Preliminary results suggest that simultaneous penetration depth, bead width, and torch position control is possible. >

IN SITU FORMATION OF THREE-DIMENSIONAL TIC REINFORCEMENTS IN TI-TIC COMPOSITES

Three-dimensional, single-crystal reinforcements of TiC were producedin situ during manufacture of Ti-TiC composites. The composites, containing 40 to 50 vol pct TiC, were produced using standard casting procedures. The presence of aluminum in Ti-TiC composites showed enhanced strength without loss of ductility at room and elevated temperatures. Aluminum additions were found to solid solution strengthen the Ti matrix and increase the strength of the TiC phase. The morphology of the TiC, which was controlled by processing parameters, influenced the properties of the Ti-TiC composites investigated. Refinement of the secondary dendrite arm spacing of the three-dimensional (3-D) TiC particles was found to dramatically improve the ultimate tensile strength (UTS) and ductility of the Ti-TiC composites.

Comparison of the in-reactor creep of selected ferritic, solid solution strengthend, and precipitation hardened commercial alloys

Abstract The results of an in-reactor creep experiment designed to compare the creep behavior of nine commercial alloy compositions and one modified composition in various heat treatments are presented. Data are reported for one temperature, 540°C, after accumulated nominal fluences of 2 and 4 × 10 22 n / cm 2 ( E > 0.1 MeV ). Selected ferritic, solid solution strengthened and precipitation hardened alloys of the Fe-Cr-Ni system were investigated. In general, the high strength precipitation hardened alloys have the greatest resistance to in-reactor creep. Thermomechanical heat treatments are shown to influence the creep behavior. The results when compared with a semi-empirical creep equation, suggest a possible interrelation between irradiation creep and swelling.

Rapid and sensitive detection of Salmonella Typhimurium on eggshells by using wireless biosensors.

This article presents rapid, sensitive, direct detection of Salmonella Typhimurium on eggshells by using wireless magnetoelastic (ME) biosensors. The biosensor consists of a freestanding, strip-shaped ME resonator as the signal transducer and the E2 phage as the biomolecular recognition element that selectively binds with Salmonella Typhimurium. This ME biosensor is a type of mass-sensitive biosensor that can be wirelessly actuated into mechanical resonance by an externally applied timevarying magnetic field. When the biosensor binds with Salmonella Typhimurium, the mass of the sensor increases, resulting in a decrease in the sensors resonant frequency. Multiple E2 phage-coated biosensors (measurement sensors) were placed on eggshells spiked with Salmonella Typhimurium of various concentrations (1.6 to 1.6 × 10(7) CFU/cm(2)). Control sensors without phage were also used to compensate for environmental effects and nonspecific binding. After 20 min in a humidity-controlled chamber (95%) to allow binding of the bacteria to the sensors to occur, the resonant frequency of the sensors was wirelessly measured and compared with their initial resonant frequency. The resonant frequency change of the measurement sensors was found to be statistically different from that of the control sensors down to 1.6 × 10(2) CFU/cm(2), the detection limit for this work. In addition, scanning electron microscopy imaging verified that the measured resonant frequency changes were directly related to the number of bound cells on the sensor surface. The total assay time of the presented methodology was approximately 30 min, facilitating rapid detection of Salmonella Typhimurium without any preceding sampling procedures.

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