Simple Colorimetric Sensor Rapidly Detects Food Contamination Using a Nucleic Acid Probe
A team of researchers have developed an easy-to-use colorimetric
assay for the detection of food contaminated with salmonella. The assay
is based on a novel nucleic acid probe that is cleaved by an RNase
enzyme specific to the salmonella species. As the team report in the
journal Angewandte Chemie, this specific enzymatic cleavage
principle made it possible to build a sensitive but simple and portable
test system using colloidal gold.
© Wiley-VCH, re-use with credit to 'Angewandte Chemie' and a link to the original article.
Consumption of food contaminated with Salmonella typhimurium,
whether eggs, ground meat, or chicken, can lead to severe food
poisoning. However, suspected cases of salmonella are usually only
confirmed several days later, when the bacteria are detected in
microbiology laboratories by growing them in culture. A team of
researchers led by Yingfu Li, Tohid Didar, and Carlos Filipe of McMaster
University in Hamilton, Canada, have now developed a novel test system
based on a hybrid DNA-RNA probe that specifically and rapidly detects
salmonella, without the need for microbiological diagnostics or
expensive analytical equipment.
Using a multi-round selection process, the McMaster team uncovered an
artificial DNA-RNA hybrid probe that is a substrate for a
salmonella-specific form of an RNase H enzyme. Based on this highly
specific enzymatic recognition, the team first developed a
fluorescence-based assay on salmonella RNase H, and then extended the
principle to a simple, portable salmonella assay based on a colloidal
gold colorimetry.
Colloidal gold is a common color reagent familiar to many of us from
its use in SARS-CoV-2 antigen test strips. In a slight departure from
this methodology, however, the team did not use a paper strip as the
basis for their assay, but instead turned to plastic pipette tips, which
are commonly used in the laboratory to measure specific amounts of
liquids.
For the preparation of the colorimetric assay, the inner wall of a
pipette tip was first coated with DNA-functionalized nanogold. A mixture
of reagents composed of nanogold-DNA and the DNA-RNA probe were then
sucked up into the pipette tip, causing a double layer of nanogold to
form on the walls, because the DNA-RNA hybrid probe links both layers.
However, when the sample mixture contains salmonella, the upper layer
is released thanks to the salmonella RNase H specifically cleaving the
DNA-RNA linker probe. When the gold-containing solution is then drained
onto an absorbent pad with a nylon membrane, a clear red spot indicates
the presence of salmonella in the sample being tested. The team also
tested the specificity of their system, finding it did not falsely
detect the presence of other bacteria containing RNAse H.
The authors highlight that the test is not only much less complex
than other methods for detecting salmonella, but also much faster. In
contrast to other methods, only one hour of incubation in a pipette tip
is required for highly sensitive detection of salmonella, for example,
in ground beef. In the future, the team envision developing more nucleic
acid probes which can specifically detect other infectious pathogens,
for example coliform bacteria such as E. coli.
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About the Author
Yingfu Li is a
professor at the Department of Biochemistry and Biomedical Sciences,
McMaster University, Hamilton, Ontario, Canada. The Li Lab has their
research interests at the interface between chemistry and biology,
examining unusual functions of nucleic acids in a creative way to apply
them for therapeutics, biomolecular detection, drug discovery and
nanotechnology. Dr. Tohid Didar is an associate professor in the
Department of Mechanical Engineering at McMaster University,
investigating smart nano-biomaterials for applications in diagnostics,
therapeutics, and food safety. Dr. Carlos Filipe is a professor and
Chair in the Department of Chemical Engineering at McMaster University,
with his research interests being at the intersection of biochemistry
and chemical engineering with a prime focus on the development of
simple-to-use biosensors.