Toxic levels of naturally occurring fluoride impact the water supply for tens of millions of people worldwide. The lack of relevant, accurate and low-cost testing options has been addressed by the development of an easy-to-use biosensor for fluoride detection.

A naturally occurring fluoride sensing mechanism from Bacillus cereus was successfully engineered into a biosensor capable of detecting fluoride levels as low as 1 ppm and incorporated into a point-of-use fluoride test. The system devised by researchers from Northwestern University, Nairobi University (Kenya) and Moi University (Kenya) consists of a freeze-dried biosensing reaction that, when rehydrated with a water sample of interest, produces a visible yellow color in the presence of fluoride within hours.

The biosensor was field-tested in a region of Kenya with known geogenic fluoride contamination. Results were compared with those from the gold-standard fluoride photometer method, and the ability of non-expert users to easily interpret the findings was examined as a key indicator that the technology can have meaningful impact in addressing global and regional water issues.

The point-of-use device was demonstrated to have an 84% chance of correctly predicting fluoride levels above the World Health Organization limit of more than 1.5 parts per million. The testing protocol was also confirmed to be highly usable by non-professionals, with only 1 of 57 tests flagged by interpretation discrepancy between the user and scientific team.

Potential next steps for the point-of-use fluoride test detailed in Nature Partner Journals: Clean Water could include mapping where geogenic fluoride hotspots occur globally.