Quantum dot lateral flow test strip for E. coli detection.

Big 7 E. coli Detection: Are New Quantum Dot Tests the Future of Food Safety?

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Soraya Malik in Health & Wellness December 2025 • 4 min read.

"Discover how innovative aptamer-quantum dot lateral flow test strips are revolutionizing the detection of pathogenic E. coli, offering faster, more sensitive food safety solutions."


For nearly a century, identifying bacteria has largely relied on serotyping, a method involving specific antibodies. This approach remains popular due to its speed and simplicity. In the realm of food safety, particularly concerning Escherichia coli (E. coli), rapid and accurate detection is crucial to prevent outbreaks and protect public health.

Traditional methods of serotyping, while effective, can be complex and time-consuming, especially when dealing with the diverse range of E. coli strains. The outer O antigens of lipopolysaccharide (LPS) on Gram-negative bacteria, including E. coli, serve as key targets for serotyping. However, the structural complexity of these antigens poses challenges for developing specific antibodies or nucleic acid aptamers.

New research explores innovative aptamer-quantum dot lateral flow test strips designed to detect the 'Big 7' pathogenic Shiga-toxin producing E. coli (STEC) serovars. These tests incorporate DNA aptamers, selected for their affinity to the LPS of these dangerous E. coli strains, combined with the sensitivity of quantum dots, offering a promising avenue for rapid and sensitive E. coli detection.

Aptamer-Quantum Dot Lateral Flow Assays: How They Work

Quantum dot lateral flow test strip for E. coli detection.

The core of this innovation lies in the combination of aptamers and quantum dots. Aptamers are single-stranded DNA or RNA molecules that can bind to specific target molecules with high affinity, similar to antibodies. Quantum dots, on the other hand, are semiconductor nanocrystals that emit bright, fluorescent light when exposed to UV light.

In these lateral flow assays, aptamers specific to the LPS of the 'Big 7' E. coli serovars are conjugated to quantum dots. When a sample containing the target E. coli serovars is applied to the test strip, the aptamer-quantum dot conjugates bind to the bacteria. This complex then migrates along the test strip, where it is captured by another aptamer immobilized on a test line.

  • The accumulation of quantum dots at the test line results in a fluorescent signal that can be easily visualized under UV light.
  • The intensity of the fluorescent signal is proportional to the amount of target E. coli present in the sample.
  • This allows for rapid and semi-quantitative detection of the 'Big 7' E. coli serovars.
The study evaluated the performance of these aptamer-quantum dot lateral flow assays against a panel of live 'Big 7' E. coli serovars, related bacterial species, and unrelated bacterial species. While some cross-reactivity was observed, the assays generally demonstrated a preference for their cognate E. coli serovars. Prototype test strips for E. coli O26 and O45 showed the most specificity, with the O26 test strips exhibiting a detection limit of 15 to 150 viable bacterial cells per test.

The Future of E. coli Detection

This research highlights the potential of aptamer-quantum dot lateral flow assays as a rapid and sensitive tool for detecting pathogenic E. coli in food samples. The ability to detect low levels of bacteria in a short amount of time makes these tests particularly valuable for screening and triaging samples.

While further optimization is needed to improve specificity and reduce cross-reactivity, these tests offer a promising alternative to traditional methods of E. coli detection. Coupling these tests with confirmatory genetic techniques, such as PCR or DNA sequencing, can provide a comprehensive approach to food safety testing.

As the food safety testing industry continues to evolve, incorporating aptamers with improved specificity could lead to the development of highly serovar-specific LF assays for all current and future STEC serovars, ensuring safer food and better public health outcomes.

About this Article -

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Everything You Need To Know

1

What is serotyping, and why is it important in E. coli detection?

Traditional serotyping identifies bacteria using specific antibodies and targets the outer O antigens of lipopolysaccharide (LPS) on Gram-negative bacteria like E. coli. It's favored for its speed and simplicity in food safety applications. However, this method can be time-consuming, particularly given the structural complexity and diversity of E. coli strains. New approaches are needed to improve both speed and accuracy.

2

How do aptamer-quantum dot lateral flow assays work to detect E. coli?

Aptamer-quantum dot lateral flow assays combine the specific binding capabilities of DNA aptamers, which target the LPS of the 'Big 7' Shiga-toxin producing E. coli (STEC) serovars, with the fluorescent properties of quantum dots. The aptamers bind to E. coli, and the quantum dots emit a detectable signal, allowing for rapid and sensitive detection.

3

Can you explain the step-by-step process of how E. coli is detected using aptamer-quantum dot lateral flow assays?

In aptamer-quantum dot lateral flow assays, aptamers specific to the LPS of the 'Big 7' E. coli serovars are attached to quantum dots. If the targeted E. coli serovars are present in a sample, the aptamer-quantum dot conjugates will bind to the bacteria, migrate along the test strip, and be captured by immobilized aptamers. The resulting accumulation of quantum dots generates a fluorescent signal under UV light, signaling the presence of E. coli. The intensity of this fluorescence indicates the quantity of E. coli in the sample, providing semi-quantitative detection.

4

How specific and sensitive are aptamer-quantum dot lateral flow assays in detecting the 'Big 7' E. coli?

Aptamer-quantum dot lateral flow assays showed a preference for their cognate E. coli serovars. Prototype test strips for E. coli O26 and O45 exhibited the best specificity, with the O26 test strips being able to detect between 15 to 150 viable bacterial cells per test. While the study showed promising results, some cross-reactivity with related bacterial species was also observed.

5

What are the potential implications of using aptamer-quantum dot lateral flow assays for food safety, and what challenges need to be addressed for broader adoption?

Aptamer-quantum dot lateral flow assays offer rapid and sensitive detection, making them valuable for quickly screening food samples. This can significantly reduce the time needed to identify contamination. This method can improve public health by enabling faster responses to potential outbreaks. However, broader adoption would require addressing the observed cross-reactivity issues to ensure accurate and reliable results across a wider range of sample types. Additionally, to fully replace traditional serotyping, the aptamer-quantum dot method would need to be cost-competitive and easily adaptable to different testing environments.

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