Paper-based sensor monitors food iron levels

University of Illinois develops food sensor
University of Illinois researchers have developed an affordable, reliable paper-based sensor that works with a companion cellphone app, pictured here, to detect iron levels in fortified food products. (University of Illinois)

A team of University of Illinois researchers has developed an affordable, reliable paper-based sensor that works with a companion cellphone app to detect iron levels in fortified food products.

The technology combines chemistry, engineering, nutrition, and food science to develop the color-changing paper sensor that can detect iron in food, and leverages information technology to develop the cellphone app that can be accessed by all. The research was led by Anna Waller, a doctoral candidate in the University of Illinois Department of Food Science and Human Nutrition, and the IGNITE Lab. It is published in the journal Nutrients.

“We study fortification programs as a means of reducing micronutrient deficiencies in low-income countries,” Waller explained. “One of the calls-to-action for improving the efficacy or success of these programs is ramping up the monitoring and evaluation of these programs, which is lacking in a lot of low-income settings. But to do so involves so much laboratory infrastructure and personnel that often is not available in these settings.”

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Juan Andrade, an associate professor of nutrition in the department and co-author of the study, explained the key role that trust between consumers, the companies who process the food products, and the governments who regulate the fortification programs played in developing the sensor.

“At the end of the day, you have a tool that everybody agrees upon, that is valid, simple, and low-cost, that gives you results on a cellphone. If the phone can connect to the cloud, and the cloud is connected to a government office or the company’s office, they can monitor and maintain the records that support their claims. Everything is collected and stored. There is no room for disagreement. That is why this is a great technology to bring about.”

Waller investigated various biosensors and found that paper-based sensors were the least expensive and easiest to use. She tested papers that would support the development of the color spot they were measuring, and settled on a hydrophobic paper, which is embedded with silicone. This reduced the heterogeneity of the color spot on the paper, and provided a more accurate and reliable output. 

Using her chemistry background, Waller then researched different reactions with iron that could produce a visible color change on the paper, landing on the ferrozine reaction, which works in the widest range of temperatures. She reduced the amount of the liquids in the solution to a small microliter amount, put it on the paper, and dried it.

This process resulted in the paper-based assay that changes color in response to iron in fortified foods. The researchers used Tanzanian wheat flour and infant formula that had already been fortified to test their sensor. They fortified corn flour in the study with iron to levels that the World Health Organization recommends.

With help of a grant from the ADM Institute for Postharvest Loss, the researchers then developed  a smartphone app, in collaboration with University of Illinois Technology Services, to quantify this color change. With a mobile phone, those who would be evaluating nutrient levels in fortified food take a photo of the paper sensor, after colors show up, and the app analyzes the iron levels.

According to Andrade, the traditional method for measuring iron in food samples is using atomic absorption or emission spectroscopy. This type of analysis can be expensive, requires trained personnel, and is usually only found in laboratories at universities or private industries.