Inexpensive microbial dipstick diagnostic for nitrate in water

Kelly G. Aukema, Lawrence P. Wackett

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


Amid growing global concern over nitrate contamination of water supplies, there is increasing need for inexpensive, easy-to-use methods for determining nitrate (NO 3 - -N). In response, we report the development of a low cost, rapid, portable, colorimetric paper bio-strip for determining nitrate in various types of water. The biosensor designed here used E. coli cells impregnated into paper to reduce nitrate to nitrite stoichiometrically. One aspect of the design novelty was to prime the cells with formate allowing quantitative formation of nitrite. The nitrite formed in the paper was then reacted with reagents to produce a high extinction coefficient, maroon-color azo-dye. The azo dye color was calibrated to allow quantitative detection of nitrate in water via visual inspection or smart phone applications. The strips accurately determined nitrate in drinking water samples within 2 ppm error. The optimum range of NO 3 - -N concentrations detected is 1-10 ppm. Most regulatory agencies set 10 ppm NO 3 - -N as the highest acceptable limit, and suitable dilutions can be used above that range. The potential co-contaminants lead, sulfate, chromate, borate, and cadmium did not interfere with the nitrate bio-strip, unlike a current commercially available rapid test kit that is negatively impacted by lead. Moreover, the projected life time of the current bio-strip stored at room temperature was over one year, as determined by accelerated aging experiments. In total, this describes a stable, accurate, interference-resistant, portable, and lightweight testing material for nitrate that can be prepared for a few cents per test.

Original languageEnglish (US)
Pages (from-to)406-416
Number of pages11
JournalEnvironmental Science: Water Research and Technology
Issue number2
StatePublished - Feb 2019

Bibliographical note

Funding Information:
This research was supported by grants from the University of Minnesota Grand Challenges Initiative and the Legislative-Citizen Commission on Minnesota Resources. The authors thank Julie Johnson and Sebastian Behrens for nitrate flow analysis, Mike Sadowsky for E. coli MG1655, and Jon Sakkos for help with fluorescence imaging. KGA thanks Serina Robinson and James Christenson and members of the Wackett lab for helpful discussion and James and Garrett Aukema for assembling paper strip prototypes.

Publisher Copyright:
© 2019 The Royal Society of Chemistry.


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