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Posted: Sep 06, 2017
Detecting food allergens with a keychain reader
(Nanowerk Spotlight) The incidence of food allergies, food sensitivities, and autoimmune reaction is increasing worldwide, particularly among children. For instance, the prevalence of adverse reactions to food in the United States in 2014 was estimated to be 5% for adults and 8% for children, an
increase from 2006 estimates (3% to 4% and 6%, respectively) (source). Food allergies cost the U.S. an estimated $25 billion annually.
From the perspective of the food-allergic patient, food allergy can be difficult and time-consuming to manage because sufferers may react to extremely small amounts of problematic food. The only available treatment for food allergy is avoidance of problematic food and consequently, the implementation of effective allergen detection and/or labelling strategies is essential.
Unfortunately, many existing analytical methods and devices for food testing are designed for sophisticated laboratory rather than consumer use and rely on complex equipment, infrastructure, and advanced training.
There may be a novel solution to address this issue. Researchers have now developed a portable, point-of-use technology for rapid, integrated exogenous antigen testing (iEAT).
"Our system consists of a disposable allergen extraction device and an electronic keychain reader for sensing and communication," Hakho Lee, an Associate Professor in Radiology at Harvard Medical School, tells Nanowerk. "The extraction kit captures and concentrates food antigens from dispersed food. Captured allergens are then quantified using the miniaturized key-chain reader."
iEAT system for onsite antigen detection. (A) The system consists of a pocket-size detector, an electrode chip, and a disposable kit for allergen extraction. The detector connects with a smartphone for system control and data upload to a cloud server. (B) Antigen extraction. Antigens are captured on magnetic beads (MBs) and subsequently labeled with antibodies conjugated with oxidizing agents (HRP, horseradish peroxidase). A disposable kit has been developed to handle samples; the sheathed magnet collects and redisperses MBs. (C) For signal detection, HRP-coated MBs are mixed with electron mediators (TMB, 3,3,5,5'-tetramethylbenzidine) and dropped on the electrode. HPR catalyzes the oxidation of TMB. Electrical currents are generated when oxidized TMB is reduced on or near the electrode; ox, oxidation; red, reduction. (Reprinted with permission by American Chemical Society) (click on image to enlarge)
The team's iEAT system enables quantitative allergen detection in a short and actionable time frame (less than 10 minutes for the entire assay) at minimal cost (under $4 per assay).
"We designed iEAT specifically to promote consumer-based operations: 1) the extraction kit is simple to use, inexpensive, and disposable; 2) detection is fast, reliable, and accurate; and 3) embedded communication protocols allow users to record and upload information to a cloud server with time and locale stamps," explains Lee.
The researchers optimized their iEAT prototype to detect five representative allergens from wheat, peanut, hazelnut, milk, and egg white. The rapid iEAT assay achieved high sensitivity, far-surpassing the gold standard ELISA. They also show iEAT’s practical use in surveying common foods for these allergens.
Food allergy can result from either direct sensitization to foods or cross-reactive IgE responses to inhalant allergens. The core of the iEAT functionality is an optimized antigen extraction protocol.
The team's goal was to minimize both extraction time and cost while maximizing recovery yield. They used five major protein antigens as extraction targets: gliadin (wheat), Ara h1 (peanut), Cor a1 (hazelnut), casein (milk), and ovalbumin (egg white).
The iEAT detection is based on the combination of magnetic enrichment and electrochemical sensing. The predetermined target antigens are captured on immunomagnetic beads (2.8 µm in diameter; prepared by conjugating monoclonal antibodies to magnetic beads) and then these beads are used as a solid substrate for electrochemical reaction. The ultimate signal (electrical current) is then read out.
A key advance of the team's approach is the development of a portable sensing system.
Microcontrollers (e.g., Raspberry Pi, Arduino) have become a powerful tool – they are now used in almost every consumer electronics and connected to each other (Internet of Things). The scientists' idea was to use this cutting edge technology for personal health and medical diagnostics.
The iEAT system can be used for on-site food detection. The detection kit (dongle) is small and easy to use; and the sensing is done within 10 minutes.
Pilot tests with iEAT showed a wide variation in allergen contents in packaged food products and restaurant meals. Hidden allergens (like gluten in salad dressing, likely from additives) were also found.
A next step for the researchers will be to achieve full automation. Currently, the antigen extraction and labeling is a separate process manually performed. They are already designing the next generation system that can perform the entire assay in a single integrated device – "sample-in and answer-out”.
"While we focused on specific protein antigens, the current assay format could also be modified to detect small molecules, toxins, or nucleic acids by changing affinity ligands; creating detection panels for food safety (e.g., pesticides) and for food-source identification (e.g., DNA-based testing), " Lee concludes. "This is also a platform technology. We can apply the same device to detect other targets, e.g., circulating cancer markers in blood or urine, which is also an active research area in our labs."