New Paper-Based Sensor Technology to Economically Detect Iron Levels in Fortified Foods

To address nutrient deficiencies in their populations, several low-income countries have adopted mass food fortification programs. However, many of these programs do not have the resources needed to establish if the right amount of nutrients is constantly present in those food items.

(Image credit: University of Illinois)

University of Illinois scientists have built an economical, reliable paper-based sensor that runs via a cellphone app (also developed at the University of Illinois) to detect iron levels in fortified food items.

The new technology integrates chemistry, nutrition, engineering, and food science to design the color-changing paper sensor that can identify iron in food, together with information technology to build the user-friendly cellphone app that is available in low-income settings.

Anna Waller, a doctoral candidate in the Department of Food Science and Human Nutrition, and the IGNITE Lab, headed the research. Details of the study have been published in the journal Nutrients.

We study fortification programs as a means of reducing micronutrient deficiencies in low-income countries. 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.

Anna Waller, Study Lead and Doctoral Candidate, Department of Food Science and Human Nutrition, University of Illinois

Juan Andrade, an associate professor of nutrition in the department and the study’s co-author, explains that trust between consumers, the governments who control the fortification programs, and the companies who process the food items, is paramount. The new technology, he states, addresses that trust.

“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 started by exploring various types of biosensors. “The paper-based sensor really stood out in that it seemed to be the most inexpensive and simplest to use, which aligns with the World Health Organization’s criteria for developing these types of technologies,” she adds.

One of the big challenges, Waller says, was choosing what paper substrate to use. She observed in earlier studies on paper-based sensors, that hydrophilic papers with the capacity to absorb water were frequently used.

Because we’re measuring added iron in a dried food matrix, we needed to dissolve it first into an acid solution. However, when we used the hydrophilic paper, the color spot that developed was very inconsistent and the color was not easy to measure because the sample spread on the hydrophilic paper.

Anna Waller, Study Lead and Doctoral Candidate, Department of Food Science and Human Nutrition, University of Illinois

She pursued testing papers that would boost the development of the color spot they were measuring, and decided on a hydrophobic paper, which is embedded with silicone. This minimized the heterogeneity of the color spot on the paper, and delivered a more accurate and dependable output.

Applying her experience in chemistry, she then studied diverse reactions with iron that could create a visible color change on the paper, choosing the ferrozine reaction, which works in the broadest range of temperatures. She decreased the amount of the liquids in the solution to a microliter amount, set it on the paper, and waited for it to dry.

This method has fewer interferences [with other nutrients]. It has a bright magenta color. So when you see the smear on the papers, everything is concentrated. That’s why the color is so vibrant, and it dries fast. The color is very stable and stays the same when it dries.

Juan Andrade, Study Co-Author and Associate Professor of Nutrition, University of Illinois

Andrade added, “It took a while to figure out what method, because if the color goes away, we’re done. This is a very stable reaction, and the color has stayed stable for two years.”

This process led to the paper-based assay that varies in color in reaction to iron in fortified foods. The scientists used infant formula and Tanzanian wheat flour that had already been fortified to test their sensor. They fortified cornflour in the research with iron to levels recommended by the World Health Organization.

The team also was given a grant from the ADM Institute for Postharvest Loss to create a smartphone app, in partnership with University of Illinois Technology Services, to measure this color change using the smartphone application. With a cellphone, those who would be assessing nutrient levels in fortified food click a photo of the paper sensor, after colors appear, and the app evaluates the iron levels.

Conventionally, the gold standard technique for measuring iron in food samples, Andrade explains, is the use of emission or atomic absorption spectroscopy. However, this type of examination can be costly, necessitates trained workers, and is typically only found in laboratories at private industries or universities.

But Andrade explains that smartphones are available in low-resource settings. “Studies show there is a penetration of cellphones in low-income countries. We have been there, and we understand the context, so we bring that to the design of these paper-based technologies.”

Waller went to Mexico on a Fulbright Fellowship to corroborate the sensor’s accuracy and reliability in sensing iron using foods from an actual fortification program, in comparison to the traditional technique of assessing nutrient levels.

In addition to developing a low-cost sample preparation kit that provides valid, accurate, and dependable measurements, one of the experiments she performed in Mexico was to compare how the smartphone app results matched against results on a desktop computer using the software.

Andrade explained, “One of the aspects published in this paper is the seamless transition from a desktop- to a smartphone-based analysis without jeopardizing sensor performance and validity,”

“In our initial studies, we took a photo with a cell phone or camera, digitized it, and analyzed it using computer software. But what if the phone itself does the analysis instead of taking it to a desktop computer? Will the value obtained be these same? That’s what we had to test, and the answer is yes,” he added.

Andrade states that the validation of paper-based assays is paramount. “Many labs develop innovative detection platforms, but few validate their technologies in the field,” he added.

The paper, “Development of a paper-based sensor compatible with a mobile phone for the detection of common iron formulas in fortified foods within resource-limited settings,” has been published in Nutrients [DOI: 10.3390/nu11071673].

Co-authors include Anna W. Waller, Marco Toc, Dylan J. Rigsby, Marcela Gaytan-Martinez, and Juan Andrade. Waller, Toc, and Andrade are all in the Department of Food Science and Human Nutrition in the College of Agricultural, Consumer and Environmental Sciences at the University of Illinois.

The research received partial funding from the ADM Institute for Postharvest Loss, The Fulbright-Garcia-Robles Fellowship (Waller), the Jonathan Baldwin Turner Fellowship (Waller), and USDA Hatch funds [ILLU-698-904.


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