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Escherichia coli O157:H7 is an important cause of foodborne diseases with symptoms of diarrhea,
hemorrhagic colitis and hemolytic uremic syndrome. Salmonella spp. are widely distributed in nature
and are a major cause of foodborne illness with symptoms of nausea, vomiting, and diarrhea in the
United States. Accurate and fast detection method for foodborne pathogens from various food
samples has always been a desirable and important goal that has attracted scientists from many
research areas. Quantum dots (QDs) are a family of nanosized particles comprised of a few
thousands atoms, with typical size 1 to 10 nm in radius. QDs have long-term stable photostability,
high quantum yield, broad absorption spectra and narrow, symmetric emission. QDs demonstrate
high signal-to-noise ratio, allowing for much improved sensitivity of QD-based detection methods.
In this study, a combination of 1-ethyl-3-(3-dimethylaminopropyl carbodiimide hydrochloride
(EDC) and protein A was used to form a crosslinker between antibodies and QDs. In addition,
bead-free immunomagnetic separation (IMS) was tested to isolate target E. coli O157:H7 and
Salmonella from ground beef products. The objective of this study was to use a bead-free IMS
method to isolate E. coli O157:H7 and Salmonella from ground beef and QD-labeled antibodies as a
reporter to detect the presence of E. coli O157:H7 or Salmonella.
Findings: This novel bead-free QD-facilitated detection method demonstrated a high fluorescence strength
compared to traditional IMS methods when the target cell concentration were equal. This indicated
that the bead-free method have high sensitivity for cell detection. This detection method was
applied to pure cultures, it detected as low as 10 CFU/ml target pure culture and 10-6 CFU/g E. coli
O157:H7 and Salmonella from ground beef simultaneously. With the incorporation of a 24-h
enrichment step, this method can detect as low as 10 CFU/g Salmonella cells from artificially
contaminated beef.