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This paper presents a method that combines surface swab sampling and wireless biosensing for rapid detection of foodborne pathogens on solid surfaces. The method can be applied to any surfaces, including the surfaces of food processing tables and fresh produce, for food safety improvement. Surface swab sampling is an inexpensive and easy-to-use method of collecting pathogens. A desired area or the whole area of a target surface (if needed) can be swabbed to collect pathogens rapidly. In this study, five commercially available swabs were compared. We first investigated the water absorption capacities of the swabs and then analyzed the efficiencies of capture and release of a model pathogen, Salmonella Typhimurium. Plate counting was employed to quantify the initially inoculated cells and collected cells by surface swabbing, and the efficiency of capture and release was calculated.

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 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.

In this paper, a phage filter has been developed to capture, concentrate and isolate small numbers of pathogens from large volumes of water. The phage filter consists of a magnetized filter frame and hundreds of phage-coated filter elements made of a magnetostrictive material. ANSYS Maxwell magnetostatic simulations have been conducted on filter designs. A prototype filter frame in the size of 2″ has been made of a PMMA pipe and Permalloy 80 wire. Two permanent magnets were used to generate a uniform magnitude of magnetic flux density and a desired direction of flux vectors to align and hold a high density of filter elements. The filter elements in the size of 4 mm × 0.8 mm × 30 µm were made of Metglas 2826MB ribbon by mechanically dicing. The experimental results were compared with the simulation models to improve the filter design.

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.

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.

Fresh specialty crop produce such as tomatoes, blueberries, strawberries, sprouts, cantaloupes, lettuce and leafy greens account for more instances of foodborne illness than any other food category. Recent announcements to consumers, by the United States (U.S.) Centers for Disease Control (CDCs), to discard all Romaine lettuce because of bacterial contamination has resulted in hundreds of millions of dollars in losses to growers and processors. Unfortunately, current microbiological testing of samples of specialty crops (whole fruits, leaves of spinach, etc.), as specified by FDA’s Bacteriological Analytical Manual (BAM), requires at least 48 hours to perform the complicated, time-consuming and costly steps of soaking, , concentration, enrichment, plate count or PCR to detect pathogens on these samples. Further complicating the BAM analyses are the realities that: 1) both PCR and ELISA are unable to distinguish between live and dead cells and 2) only a few samples out of as many as 100,000 fruits, vegetables or leaves of multi-ton batches of produce can be BAM tested. A Non-clogging Biomolecular Phage Filter has been developed to simultaneously capture, concentrate and isolate small numbers of pathogens from large volumes of produce wash water. This phage filter can then be evaluated to screen for live versus dead cells and ID the specific pathogen in minutes. Capture efficiencies of greater than 94% have been demonstrated.

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 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. 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.

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.

This paper investigates phage-coated magnetoelastic (ME) biosentinels that capture and detect low-concentration pathogenic bacteria in stagnant liquid. These biosentinels are composed of a freestanding ME resonator platform coated with a landscape phage that specifically binds with the pathogens of interest. These biosentinels can be moved through a liquid by externally applied magnetic fields. When a time-varying magnetic field is applied, the ME biosentinels can be placed into mechanical resonance by magnetostriction. As soon as the biosentinels bind with the target pathogen through the phagebased biomolecular recognition, a change in the biosentinel’s resonant frequency occurs, and thereby the presence of the target pathogen can be detected. Detection of Bacillus anthracis spores under stagnant flow conditions was demonstrated.

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.

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.

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.

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.

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.

Phage based magneto-elastic (ME) biosensors have been shown to be able to rapidly detect Salmonella in various food systems to serve food pathogen monitoring purposes. In this ME biosensor platform, the free-standing strip-shaped magneto-elastic sensor is the transducer and the phage probe that recognizes Salmonella in food serves as the bio-recognition element. According to Sorokulova et al. at 2005, a developed oligonucleotide probe E2 was reported to have high specificity to Salmonella enterica Typhimurium. In the report, the specificity tests were focused in most of Enterobacterace groups outside of Salmonella family. Here, to understand the specificity of phage E2 to different Salmonella enterica serotypes within Salmonella Family, we further tested the specificity of the phage probe to thirty-two Salmonella serotypes that were present in the major foodborne outbreaks during the past ten years (according to Centers for Disease Control and Prevention). The tests were conducted through an Enzyme linked Immunosorbent Assay (ELISA) format. This assay can mimic probe immobilized conditions on the magnetoelastic biosensor platform and also enable to study the binding specificity of oligonucleotide probes toward different Salmonella while avoiding phage/ sensor lot variations. Test results confirmed that this oligonucleotide probe E2 was high specific to Salmonella Typhimurium cells but showed cross reactivity to Salmonella Tennessee and four other serotypes among the thirty-two tested Salmonella serotypes.

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 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.

Each year in the United States, foodborne pathogens, including bacteria, viruses, and parasites, cause an estimated 48 million illnesses, 128,000 hospitalizations, and 3,000 deaths. Forty-six percent of those illnesses are attributed to fresh produce, with pathogens on leafy greens causing the most illnesses. Pathogen contamination in fresh foods is a threat to public health. Unfortunately, the microbiological testing of a few samples of whole fruits or even hundreds of spinach leaves is inadequate to ensure the safety of a batch of specialty crop produce. Similarly, microbiological testing of only a few milliliters from thousands of liters of irrigation water and wash water used to grow and process a batch of specialty crop produce is woefully inadequate. A revolutionary, non-clogging phage filter system has been developed to capture, concentrate and isolate small numbers of multiple pathogens (100 CFU) from large volumes of irrigation and wash water (1,000 liters

This paper presents the results of a preliminary investigation to develop a bio-inspired autonomous pathogen screening system that mimics the function of natural immune systems, such as white blood cells. This screening system is comprised of multiple magnetoelastic (ME) biosentinels. The sentinels are composed of a wireless magnetoelastic resonator immobilized with a bio-probe layer that captures specific target pathogens. The biosentinels are actuated, monitored, and controlled wirelessly by external magnetic fields. The autonomous sentinel system is envisioned to have the capability of seeking out invasive pathogens in liquid environments, detecting and capturing them. In the paper, the proof-in-principal of the concept of autonomous sentinels is demonstrated by comparing the response of the sentinels in dynamic and static Salmonella analytes.

This paper presents the direct detection of Salmonella typhimurium on egg shells using a phage-based magnetoelastic (ME) biosensor. The ME biosensor consists of an ME resonator as the sensor platform and E2 phage as the bio-recognition element. The bio-recognition element is genetically engineered to bind specifically with Salmonella typhimurium. The ME biosensor, a wireless sensor, vibrates with a characteristic resonant frequency under an externally applied magnetic field. Multiple sensors can easily be remotely monitored. Multiple measurement and control sensors were placed on egg shells contaminated by Salmonella typhimurium solutions with different known concentrations. The resonant frequency of sensors before and after the exposure to the spiked egg shells was measured. The frequency shift of the measurement sensors was significantly different than the control sensors indicating Salmonella contamination. Scanning electron microscopy was used to confirm binding of Salmonella to the sensor surface and the resulting frequency shift results.

An optimized, phage-based magnetoelastic (ME) biosensor method was performed to detect Salmonella Typhimurium contaminates on the surface of tomatoes and to determine the detection limit. After serial inoculations of S. Typhimurium on the surface of the tomatoes, the S. Typhimurium on the surfaces was analyzed using an optimized ME biosensor method. Detection limit and sensitivity of the ME biosensor for detection of S. Typhimurium on tomatoes were determined. The resonant frequency shifts of the ME measurement sensors increased linearly with an increase in the concentration of S. Typhimurium. Contrastingly, the control sensors showed relatively constant and low magnitude frequency shifts. Detection limit and sensitivity of the ME biosensor method was determined to be (1.78 {plus minus} 0.17) log CFU/cm2 and 922.7 Hz.

This paper presents a novel lab-on-a-chip type bio-sensing system that is comprised of magnetoelastic (ME) biosensor, planar coil, and microfluidic system. The novelty of this system is to integrate planar coil to wirelessly actuate and detect the ME biosensor. Compared with solenoid coil that is traditionally used to measure ME sensors, the two-dimensional planar coil made by micro-fabrication process shows advantages of easy miniaturization and integration. The ME-sensor based microfluidic-chip was fabricated. By assembling poly-L-lysine coated ME biosensors into the chip, real-time in-liquid detection of yeast cells at different concentrations was successfully performed. The results showed that continuous decrease in the resonant frequency of the ME biosensor was observed as yeast cells were attaching on the sensor surface. Significant frequency shifts were obtained when the cell binding reached equilibrium. With the in situ real-time bio-sensing capability, this highly integratable system shows great potential of being used for rapid and low-cost bio-analysis.

Efforts were made to incorporate the phage Magnetoelastic (ME) biosensor in FDA's Spinach Soaking procedures according to FDA 2015 BAM method. Three soaking materials (Lactose broth, LB broth, and Peptone water) and various soaking times were investigated. Using merely 100 Salmonella cells spiked on the produce surfaces, the phage biosensors detected Salmonella within 5 hours when soaking tomatoes in LB broth as opposed to taking up to 24 hours. Salmonella was detected on spinach leaves within 7 hours. These phage ME biosensors provide a promising rapid detection platform using LB broth in FDA's soaking procedures while shortening the incubation period.

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 paper presents a revolutionary 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) and/or enrichment. The speed of detection is from 2 to 10 minutes with a limit of detection in a range of 10^2 to 10^4 cfu/mm^2. The specificity of detection is 2 in 10^6 background bacteria. This technology was awarded a $20,000 prize in the first United States Food and Drug Administration (FDA) Food Safety Challenge. The method combines wireless magnetoelastic (ME) biosensors and a surface-scanning detector for rapid determination of bacterial contamination. Tests were conducted on tomatoes and grapes spiked with different concentrations of Salmonella Typhimurium. The resonant frequency changes of the biosensors were found to be dependent on the surface concentration of Salmonella. Detection limits were found to be affected by the surface roughness of the food. A 90-second video of a test for Salmonella on tomato can be viewed at http://eng.auburn.edu/food-safety. The method presented in this paper is envisioned for use at ports of entry for the swift screening of foods.

Amorphous metallic glasses possess a unique combination of magnetostriction and extremely soft magnetic properties making them ideal candidates for developing high performance biosensors. This paper presents the results of an investigation of novel free-standing magnetoelastic (ME) biosensors based on Fe–B amorphous metallic glasses. The principle of operation of wireless ME biosensors and the advantages of metallic glasses for their construction are discussed. The materials with the highest possible elastic–magnetic energy conversion efficiency are favored for sensor applications. Due to the unique properties of amorphous metallic glasses, acoustic wave sensors based on amorphous ME alloys with mild magnetostriction properties show a very high elastic–magnetic energy conversion efficiency. In this study, ME biosensor resonators 4 × 100 × 500 μm in size were manufactured by dual beam sputtering and non-traditional microelectronic fabrication techniques. E2 phage, genetically engineered to bind with Salmonella typhimurium , was immobilized on the sensor surfaces as a bio-recognition element. The detection of Salmonella in liquid using these phage-based ME biosensors was demonstrated. The ME biosensor exhibited high sensitivity and a detection limit better than 50 CFU/mL.

Plants emit phytochemicals (volatile organic compounds) as a defensive mechanism to protect themselves from insect herbivores and parasites. One of the most common phytochemicals excreted in response to bark beetle infestations is $\gamma$ -terpinene. The goal of this investigation is to develop a simple, low-cost sensor that could be used to detect these volatile organic compounds and hence early stages of insect infestations. The sensor is composed of a silicon-based substrate with interdigitated electrodes and an active sensing film, poly3-hexylthiophene (P3HT). The effect of varying morphology of the P3HT film on sensor performance is investigated. Morphology of the P3HT thin film is varied by using different solvents and casting methods. The casting methods investigated are spin coating and drop casting. The solvents under investigation are chloroform and toluene. Chloroform is found to be a better solvent while spin coating is the better casting method. This paper also investigated the sensor mechanism of P3HT sensors. Atomic force microscopy images showed structures that are consistent with a model in which the resistance increase of the chemi-resistor sensors is due to adsorption of analyte within crystalline regions. This adsorption reduced the mobility of the charged carriers.

This study presents an investigation of the effect of incubation time on the binding of Salmonella Typhimurium ( Salmonella ) with E2 phage-based magnetoelastic (ME) biosensors. After inoculation of Salmonella on a tomato surface, the attachment and existence of Salmonella on the tomato surface was observed using scanning electron microscopy (SEM). Measurement sensors with immobilized E2 phage and control sensors devoid of phage were placed on the inoculated tomato surface and incubated for various times. The extent of binding of Salmonella to the ME biosensors was determined by measuring the resonant frequency shift of the sensors and confirmed by SEM. The attachment of Salmonella on the tomato surface increased as the inoculation concentration increased. Significant increases in the frequency shifts for the measurement sensors were observed between 15 and 30 min ( P Salmonella binding with E2 phage whereas longer incubation times increased non-specific attachment from residual nutrients on the tomato surface. In contrast, there was either no or negligible binding of Salmonella on the control sensors. This study will contribute to the development of a practical protocol for the ME biosensor method.

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 sensor's 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.

One of the important applications for which phage-immobilized magnetoelastic (ME) biosensors are being developed is the wireless, on-site detection of pathogenic bacteria for food safety and bio-security. Until now, such biosensors have been constructed by immobilizing a landscape phage probe on gold-coated ME resonators via physical adsorption. Although the physical adsorption method is simple, the immobilization stability and surface coverage of phage probes on differently functionalized sensor surfaces need to be evaluated as a potential way to enhance the detection capabilities of the biosensors. As a model study, a filamentous fd-tet phage that specifically binds streptavidin was adsorbed on either bare or surface-functionalized gold-coated ME resonators. The surface functionalization was performed through the formation of three self-assembled monolayers with a different terminator, based on the sulfur-gold chemistry: AC (activated carboxy-terminated), ALD (aldehyde-terminated), and MT (methyl-terminated). The results, obtained by atomic force microscopy, showed that surface functionalization has a large effect on the surface phage coverage (46.8%, 49.4%, 4.2%, and 5.2% for bare, AC-, ALD-, and MT-functionalized resonators, respectively). In addition, a direct correlation of the observed surface phage coverage with the quantity of subsequently captured streptavidin-coated microbeads was found by scanning electron microscopy and by resonance frequency measurements of the biosensors. The differences in surface phage coverage on the differently functionalized surfaces may then be used to pattern the phage probe layer onto desired parts of the sensor surface to enhance the detection capabilities of ME biosensors.

One of the important applications for which wireless phage-immobilized magnetoelastic (ME) biosensors are being developed is the real-time detection of pathogenic bacteria for bio-security and food safety. Until now, such ME biosensors have been manufactured by immobilizing a phage probe on gold-coated ME sensor platforms via physical adsorption. Although the physical adsorption method is simple, the surface coverage as well as immobilization stability of phage probes must be evaluated as a potential way to enhance the performance of the ME biosensors. In addition, recent studies have shown that chemical immobilization of phage probes potentially improves the performance of phage-based bio/chemical sensors. Hence, we here present performance comparisons between phage-immobilized ME biosensors manufactured by different phage immobilization methods: physical adsorption and covalent attachment. The biosensor's performance was found to be directly related to the surface phage coverage.

Magnetoelastic sensors show a resonance frequency decrease once target pathogens are attached to the sensors and thus add a small mass to the sensors. These sensors are fast, sensitive, and have higher mass sensitivity with smaller sized sensors. However, signals from smaller sensors are weaker and have more noise due to manufacturing defects. In this paper, we present a pulse biosensor system that is able to avoid bias magnetic field and allows simultaneous detection using multiple sensors. With multi-sensors, the effect of a manufacturing defect is decreased and we get the benefit of averaging for more accurate and reliable results. Stability tests show that the variance of frequency detection is less than 122 ppm of its resonance frequency. Real detection of pathogen is demonstrated using Salmonella typhimurium and the results show that multiple magnetoelastic biosensors are able to detect S. typhimurium simultaneously and offer good sensitivity and reliability.

Salmonella Typhimurium on fresh tomato surface using phage-based magnetoelastic (ME) biosensors. The ME biosensors are composed of a ME resonator platform that is coated with filamentous E2 phage (genetically engineered to bind with Salmonella). Actuated and detected through magnetic field, the ME biosensors are wireless sensors. In this study, tomato surfaces were spiked with a known number of Salmonella cells and then allowed to dry in air. The detection was conducted by directly placing ME biosensors on the spiked surface. Measurements of the resonance frequencies of both control and measurement ME biosensors were made prior to the placement and after 30 minutes of the placement. Shifts in the resonance frequency of the measurement biosensors were observed while control sensors showed negligible change. The specific binding of Salmonella to the biosensors was verified by Scanning Electron Microscopy (SEM). The results indicate that this methodology may provide real-time pathogen detection without traditional sampling process.

Foodborne illness is a common public health problem because food can be contaminated by pathogens at any point from farm to dinner table. This paper shows a comparison of capturing a small quantity of a specific bacterial pathogen in a large volume of liquid using a biomolecular filter immobilized with different bioreceptors. The filter consists of support frames, which are made of a soft magnetic material, and solenoid coils for magnetization/demagnetization of the frames. The biomolecular filter is a planar, multi-layered arrangement of strip-shaped magnetoelastic (ME) biosensors with bioreceptor immobilization. These ME biosensors are magnetically held and arrayed on the filter frames. The pathogen of interest in a large volume of liquid is captured by the bioreceptor immobilized on the ME biosensors, when a large volume of liquid passes through. At the same time, non-specific debris can be passed through the biomolecular filter, in order to avoiding a common clogging issue from conventional bead filters. In this work, E2 phage and antibody, are immobilized each on ME biosensors to capture Salmonella Typhimurium in a large volume of water. The capture efficiencies and effects of multiplication of filter layers with E2 phage and the antibody on Salmonella capture efficiency will be discussed.

Swabbing, as an inexpensive, easy-to-use, and widely accepted sampling method, has been used to help magnetoelastic (ME) biosensing system for the surface pathogen quick detection. This paper introduced a modification method using a surfactant, Tween20, to help to improve the recovery rate of different swabs. In our previous research, swabbing substituted the direct ME sensor detection on the sample surfaces, which improved the detection area of one sensor from 0.2X1 mm2 into 30X30 mm2. This amendment altered the former surface spot measurement into a large area measurement. To improve the accuracy of this swabbing technique to a better level, a higher recovery rate is needed. Tween20, a stable and relatively non-toxic surfactant, was employed to modify the fibers of swabs so that after the pathogens are picked up, they would be easier to be released into DI water and detected by ME sensors. In this research, traditional swabs, such as cotton-tipped, rayon-tipped, and novel flocked swabs are used for comparison.

Zero-order or concentration independent release kinetics are highly desirable from drug delivery devices. In this paper we demonstrate experimentally, for the first time, zero-order release of a small molecular weight therapeutic, ketotifen fumarate (MW=425), from molecularly imprinted hydrogels used as therapeutic contact lenses. We performed dynamic, in vitro drug release studies from imprinted hydrogel contact lenses within a novel microfluidic device that simulates the volumetric flow rates, tear volume and tear composition of the eye. Imprinted gels with multiple functional monomers and complexation points to the drug demonstrated a significantly delayed release of drug compared to less functionalized systems. There were no statistical differences in experimentally determined equilibrium swollen polymer volume fractions, which correlate with molecular weight between crosslinks and mesh size of the gel. Under infinite sink conditions, imprinted contact lenses demonstrated Fickian (concentration dependent) release kinetics with diffusion coefficients ranging from 4.04 x 10(-9) to 5.57 x 10(-10) cm(2)/s. The highest functionalized gel exhibited a diffusion coefficient averaging ten times smaller than less functionalized gels and released drug for over 5 days with 3 distinct rates of release. Under physiological volumetric flow rates, the release rate was constant for a duration of 3.5 days delivering a therapeutically relevant dosage and was fit to a power law model indicating zero-order release characteristics with n=0.981+/-0.006 (r(2)=0.997). This work demonstrates the potential of micro/nanofluidic devices to determine physiological release rates and stresses the importance of matching local conditions to adequately characterize drug delivery devices. It also demonstrates the enormous potential for molecular imprinting to further tailor therapeutic release kinetics via the imprinting process.

The wireless phage-based magnetoelastic (ME) biosensor has proven to be promising for real-time detection of pathogenic bacteria on fresh produces. The ME biosensor consists of a freestanding ME resonator as the signal transducer and filamentous phage as the biomolecular-recognition element, which can specifically bind to a pathogen of interest. Due to the Joule magnetostriction effect, the biosensors can be placed into mechanical resonance when subjected to a time-varying magnetic field alternating at the sensor’s resonant frequency. Upon the attachment of the target pathogen, the mass of the biosensor increases, thereby decreasing its resonant frequency. This paper presents an investigation of blocking reagents immobilization for detecting Salmonella Typhimurium on fresh food surfaces. Three different blocking reagents (BSA, SuperBlock blocking buffer, and blocker BLOTTO) were used and compared. The optical microscope was used for bacterial cells binding observation. Student t-test was used to statistically analysis the experiment results. The results shows that SuperBlock blocking buffer and blocker BLOTTO have much better blocking performance than usually used BSA.