Jianguo Xi

The combination of magnetoelastic (ME) wireless biosensing with surface swab sampling

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.

Isolation of highly selective phage-displayed oligopeptide probes for detection of listeria monocytogenes in ready-to-eat food

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.

Capture of bacterial pathogens in liquid streams by multiple layers of phage based bio-molecular filter

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.

Automated surface-scanning detection of pathogenic bacteria on fresh produce

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 sensors 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.

Specificity tests of an oligonucleotide probe against food-outbreak salmonella for biosensor detection

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.