16 Methods for Detecting Microbial Pathogens in Food and Water

2D transition metal dichalcogenides with glucan multivalency for antibody-free pathogen recognition

The ability to control the dimensions and properties of nanomaterials is fundamental to the creation of new functions and improvement of their performances in the applications of interest. Herein, we report a strategy based on glucan multivalent interactions for the simultaneous exfoliation and functionalization of two-dimensional transition metal dichalcogenides (TMDs) in an aqueous solution. The multivalent hydrogen bonding of dextran with bulk TMDs (WS₂, WSe₂, and MoSe₂) in liquid exfoliation effectively produces TMD monolayers with binding multivalency for pathogenic bacteria. Density functional theory simulation reveals that the multivalent hydrogen bonding between dextran and TMD monolayers is very strong and thermodynamically favored (ΔE_b = −0.52 eV). The resulting dextran/TMD hybrids (dex-TMDs) exhibit a stronger affinity (K_d = 11 nM) to Escherichia coli O157:H7 (E. coli) than E. coli-specific antibodies and aptamers. The dex-TMDs can effectively detect a single copy of E. coli based on their Raman signal.

The detection of pathogenic microorganisms is key consideration for safety across a wide range of fields. Here, the authors report on the simultaneous exfoliation and functionalisation of transition metal dichalcogenides with dextran for antibody-free detection of pathogenic Escherichia coli.

Quantification of E. coli DNA on a flow-through chemiluminescence microarray readout system after PCR amplification

We report on a hybridization assay using DNA microarrays for the quantification of amplification products of the uidA gene of E. coli. Using the stopped-PCR strategy, the amplified target DNA was strongly dependent on the applied gene copies. The quantification was carried out by a flow-through chemiluminescence microarray readout system. The DNA microarrays were based on a poly(ethylene glycol)-modified glass substrate. The probes on the surface were 18 or 25 nucleotides long and the quantified PCR product was 60 nucleotides. The amplification was stopped after 25 cycles; at this point amplification was in the middle of the logarithmical phase, and the spread between different DNA starting concentrations reached the maximum. A conjugate of streptavidin and horseradish peroxidase (HRP) bound to the biotinylated strands on the microarray surface and catalyzed the reaction of luminol and hydrogen peroxide. The generated light emission was recorded by a sensitive charge-coupled device (CCD) camera. The detection limit for the gene uidA (beta-galactosidase) of E. coli was 1.1 x 10(5) copies/mL. This system allowed for a sensitive detection and quantification of E. coli in a concentration range from 10(6) to 10(9) copies/mL.

Flow-through immunofiltration assay system for rapid detection of E. coli O157:H7

A flow-through amperometric immunofiltration assay system based on disposable porous filter-membranes for rapid detection of Escherichia coli O157:H7 has been developed. The analytical system utilizes flow-through, immunofiltration and enzyme immunoassay techniques in conjunction with an amperometric sensor. The parameters affecting the immunoassay such as selection of appropriate filter membranes, membrane pore size, antibody binding capacity and the concentrations of immunoreagents were investigated and optimized. Non-specific adsorption of the enzyme conjugate was investigated and minimized. A sandwich scheme of immunoassay was employed and the immunofiltration system allows to specifically and directly detect E. coli cells with a lower detection limit of 100 cells/ml. The working range is from 100 to 600 cells/ml with an overall analysis time of 30 min. No pre-enrichment was needed. This immunosensor can be easily adapted for assay of other microorganisms and may be a basis for a new class of highly sensitive bioanalytical devices for rapid quantitative detection of bacteria.