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In 2015, the World Health Organization (WHO) estimated that over 420,000 people died from consuming pathogen contaminated food, with children under the age of 5 being the highest of risk to this cause of death.
In their report, the WHO determined that 31 agents, including bacteria, toxins, parasites, viruses and chemicals, are responsible for these foodborne diseases1. One of the most well known pathogens associated with the contamination of food is the bacteria Escherichia coli.
While E. coli is most commonly found in cows, chickens, deer, sheep, pigs and unpasteurized milk, juice and soft cheeses have also been found to carry the bacteria. Some of the symptoms associated with such foodborne illnesses include nausea, vomiting, and diarrhea in the short term, as well as long-term illnesses such as kidney or liver failure, cancer, as well as brain and other neural disorders2.
Conventional methods that are available in detecting the contamination of food and water for the presence of pathogenic bacteria are available. These methods often involve cell culturing, followed by multiday techniques such as surface plasmon resonance (SPR), the polymerase chain reaction (PCR) and similar immunoassays.
While these methods are sufficient in their detection ability, there is still an ever-growing need for accurate rapid on-site detection methods that are both inexpensive and user-friendly3. While more rapid techniques are available, of which can involve either the amplification of bacterial DNA or through assays based on the interactions between the antibody and bacteria, however, these methods are often more expensive, as they require the use of specialized instruments4.
A team of researchers led by principal investigator Timothy Swager and lead author Qifan Zhang at the Massachusetts Institute of Technology (MIT) have developed a new method of pathogen detection for food safety purposes.
By utilizing complex droplets known as Janus emulsions, Swager’s team of researchers have developed a method of interaction between the liquid droplet and bacterial proteins that can be detected by naked eye or even through a smartphone device, which could significantly reduce the costs and time required for typical food safety tests.
Janus emulsions are powerful liquid droplets that are capable of sensing particles when different hemispheres are functionalized to have certain biochemical properties.
Comprised of two equally sized hemispheres, of which will either be a fluorocarbon or hydrocarbon, Janus droplets have a powerful sensing capability when these hemispheres are functionalized to have orthogonal physical and biochemical properties. The unique optical properties of Janus droplets is also due to their transparent nature that
allows light to travel through the droplets with ease. This optical sensing potential is further enhanced when the Janus surfaces are covalently modified for specific recognition purposes.
In Swager’s study Janus emulsions were modified to specifically target carbohydrate-lectin interactions present in the cell. To do so, the team of researchers designed a carbohydrate surfactant molecule that is composed of mannose sugar. This surfactant is responsible conducting a self-assembly on the top half surface of the droplet, which is where the hydrocarbon and water interface is located.
Once these molecules bind to lectin, a protein found on the surface of certain strains of E. coli, the droplets attach and become clumped together4. This clumping knocks the particles off balance, which allows light to hit them in several different directions, achieving an opaque visualization when viewed from above.
To test this, researchers placed the droplets onto a Petri dish that was set above a QR code to be scanned. When E. coli was present in the Petri dish, the clumping of the droplets prevented the QR code from being read, therefore allowing for a quick determination of the presence of bacteria4.
Researchers are hopeful that this technique can be customized to detect a variety of different pathogens that are each linked to their own specific QR code.
Further improvements in the sensitivity of the sensor, as well as optimizing the way in which the food sample preparation occurs to adequately integrate the droplets is currently being studied. Researchers are hopeful that this technique can soon become commercialized and available for public use.
- "WHO's First Ever Global Estimates of Foodborne Diseases Find Children under 5 Account for Almost One Third of Deaths." World Health Organization. 3 Dec. 2015. Web. http://www.who.int/mediacentre/news/releases/2015/foodborne-disease-estimates/en/.
- "E. Coli." FoodSafety.gov. U.S. Department of Health and Human Services, 24 Aug. 2009. Web. https://www.foodsafety.gov/poisoning/causes/bacteriaviruses/ecoli/.
- Zhang, Qifan, Suchol Savagatrup, Paulina Kaplonek, Peter H. Seeberger, and Timothy M. Swager. "Janus Emulsions for the Detection of Bacteria." ACS Central Science (2017). Web.
- Anne Trafton, MIT News Office. "New Technology Could Offer Cheaper, Faster Food Testing." MIT News. 05 Apr. 2017. Web. http://news.mit.edu/2017/cheaper-faster-food-testing-smartphone-0405.