In situ immuno-magnetic concentration-based biosensor systems for the rapid detection of Listeria monocytogenes

Antibody- and nucleic acid-based lateral flow immunoassay for Listeria monocytogenes detection

Listeria monocytogenes is an invasive opportunistic foodborne pathogen and its routine surveillance is critical for protecting the food supply and public health. The traditional detection methods are time-consuming and require trained personnel. Lateral flow immunoassay (LFIA), on the other hand, is an easy-to-perform, rapid point-of-care test and has been widely used as an inexpensive surveillance tool. In recent times, nucleic acid-based lateral flow immunoassays (NALFIA) are also developed to improve sensitivity and specificity. A significant improvement in lateral flow-based assays has been reported in recent years, especially the ligands (antibodies, nucleic acids, aptamers, bacteriophage), labeling molecules, and overall assay configurations to improve detection sensitivity, specificity, and automated interpretation of results. In most commercial applications, LFIA has been used with enriched food/environmental samples to ensure detection of live cells thus prolonging the assay time to 24-48 h; however, with the recent improvement in LFIA sensitivity, results can be obtained in less than 8 h with shortened and improved enrichment practices. Incorporation of surface-enhanced Raman spectroscopy and/or immunomagnetic separation could significantly improve LFIA sensitivity for near-real-time point-of-care detection of L. monocytogenes for food safety and public health applications.

Magnetosome-anti-Salmonella antibody complex based biosensor for the detection of Salmonella typhimurium

Epidemic Salmonellosis contracted through the consumption of contaminated food substances is a global concern. Thus, simple and effective diagnostic methods are needed. Magnetosome-based biosensors are gaining attention because of their promising features. Here, we developed a biosensor employing a magnetosome-anti-Salmonella antibody complex to detect lipopolysaccharide (somatic "O" antigen) and Salmonella typhimurium in real samples. Magnetosome was extracted from Magnetospirillum sp. RJS1 and characterized by microscopy. The magnetosome samples (1 and 2 mg/mL) were directly conjugated to anti-Salmonella antibody (0.8-200 μg/mL) and confirmed by spectroscopy and zeta potential. The concentrations of magnetosome, antibody and lipopolysaccharide were optimized by ELISA. The 2 mg/mL-0.8 μg/mL magnetosome-antibody complex was optimal for detecting lipopolysaccharide (0.001 μg/mL). Our assay is a cost-effective (60%) and sensitive (50%) method in detection of lipopolysaccharide. The optimized magnetosome-antibody complex was applied to an electrode surface and stabilized using an external magnetic field. Increased resistance confirmed the detection of lipopolysaccharide (at 0.001-0.1 μg/mL) using impedance spectroscopy. Significantly, the R² value was 0.960. Then, the developed prototype biosensor was applied to food and water samples. ELISA confirmed the presence of lipopolysaccharide in homogenized infected samples and cross reactivity assays confirmed the specificity of the biosensor. Further, the biosensor showed low detection limit (10¹ CFU/mL) in water and milk sample demonstrating its sensitivity. Regression coefficient of 0.974 in water and 0.982 in milk was obtained. The magnetosome-antibody complex captured 90% of the S. typhimurium in real samples which was also confirmed in FE-SEM. Thus, the developed biosensor is selective, specific, rapid and sensitive for detection of S. typhimurium.

Versatile nano-platform for tailored immuno-magnetic carriers

Custom immuno-magnetic devices are desirable tools for biomedical and biotechnological applications. Herein, surface active maghemite nanoparticles (SAMNs) are proposed as a versatile platform for developing tailored immuno-magnetic nano-carriers by simple wet reactions. Two examples for conjugating native and biotinylated antibodies were presented along with their successful applications in the recognition of specific foodborne pathogens. Nanoparticles were functionalized with rhodamine B isothiocyanate (RITC), leading to a fluorescent nano-conjugate, and used for binding anti-Campylobacter fetus antibodies (SAMN@RITC@Anti-Cf). The microorganism was selectively captured in the presence of two other Campylobacter species (C. jejuni and C. coli), as verified by PCR. Alternatively, SAMNs were modified with avidin, forming a biotin-specific magnetic nano-carrier and used for the immobilization of biotinylated anti-Listeria monocytogenes antibodies (SAMN@avidin@Anti-Lm). This immuno-magnetic carrier was integrated in piezoelectric quartz crystal microbalance (QCM) sensor for the detection of L. monocytogenes in milk, showing a detection limit of 3 bacterial cells. The present work presents a new category of customized immuno-magnetic nano-carriers as a competitive option for suiting specific applications. Graphical abstract ᅟ.

A novel method to detect Listeria monocytogenes via superparamagnetic lateral flow immunoassay

A novel strip test system combining immunomagnetic separation with lateral flow immunoassay (LFIA) was established for the accurate detection of Listeria monocytogenes. In this system, a pair of matched monoclonal antibodies was used to construct a sandwich immunoassay, in which superparamagnetic particles were coupled with one of the antibodies as a labeled antibody to capture the target bacteria, while the other antibody was immobilized on the detection zone. After a 20-min reaction, the strips were analyzed by a novel instrument which could detect the magnetic signal of the immunocomplex in a magnetic field. Sensitivity evaluation showed that the limit of detection (LOD) of the superparamagnetic LFIA system for L. monocytogenes was 10(4) CFU/mL, which was at least one log lower than conventional LFIA. No cross-reaction was observed when Salmonella, Escherichia coli O157:H7, or three types of harmless Listeria strains were tested. Further evaluation with actual food samples indicated that the superparamagnetic LFIA system showed 100 % concordance with real-time PCR. Therefore, this novel superparamagnetic LFIA system could be used as a rapid, sensitive, and specific method for the detection of L. monocytogenes.

hlyA gene-based sensitive detection of Listeria monocytogenes using a novel cantilever sensor

Piezoelectric cantilever sensors are shown to exhibit sensitive and selective detection based on an identifying gene from genomic extract at ~10(2)-10(3) cells of foodborne pathogen, Listeria monocytogenes (LM). The study consists of two parts: tests with synthetic genes and experiments starting with whole LM cells. A probe designed for the virulence hemolysin gene, hlyA, was immobilized on the gold-coated sensor, and hybridization detection of a synthetic target (based on hlyA) is shown to span over 6 decades in concentration. Hybridization response was confirmed using two methods: (1) the use of a fluorescent indicator for the presence of double-stranded DNA (ds-DNA) and (2) hybridization response of a secondary single-strand DNA (ss-DNA) to the unhybridized part of the target much like in the enzyme linked immunosorbent assay (ELISA) sandwich format. Hybridization of the secondary ss-DNA tagged to gold nanoparticles amplified as well as confirmed the target hybridization to the hlyA probe on the sensor. Genomic DNA from LM was extracted, sheared, and melted and was exposed to the hlyA probe on the sensor in proteinous background with and without the presence of up to 10(4) times excess nontarget genomic DNA extracted from E.coli JM 101 (EC), for the gene-specific detection of LM. Discernible detection limit of 7 × 10(2) LM cells (equivalent genomic DNA; 2.32 pg) was achieved in proteinous background. The detection limit deteriorated to 7 × 10(3) LM (23 pg of gDNA) in the presence of genomic DNA from EC. Hybridization response times were within ~90 min, thus significantly improving over the conventional detection techniques in detection time at comparable detection limit.

Rapid and sensitive immunodetection of Listeria monocytogenes in milk using a novel piezoelectric cantilever sensor

Listeria monocytogenes (LM), an important food-borne pathogen that has a high mortality rate (≈ 30%), was successfully detected within an hour at the infection dose limit of 10(3)/mL, both in buffer and milk. LM detection was demonstrated using a novel asymmetrically anchored cantilever sensor and a commercially available antibody. Sensor responses were confirmed using a secondary antibody binding step, similar to the sandwich ELISA assays, as a means of signal amplification that also reduced the occurrence of false negatives. Detection of LM at a concentrations of 10(2)/mL was achieved, by incorporating a third antibody binding step, which is an order of magnitude smaller than the infection dose (<1000 cells) for LM. The commercially available antibody for LM used in this work is shown to have low avidity which partially explains the relatively low sensitivity reported for LM as compared to other pathogens.