The discovery of lead in Flint, Michigan's drinking water drew renewed attention to the health risks posed by the metal. Now researchers at the University of Houston have created an inexpensive system using a smartphone and a lens made with an inkjet printer that can detect lead in tap water at levels commonly accepted as dangerous.

The system builds upon earlier work by Wei-Chuan Shih, associate professor of electrical & computer engineering, and members of his lab, including the discovery of an inexpensive elastomer lens that can convert a basic smartphone into a microscope.

The latest discovery, described in the journal Analytical Chemistry, combines nano-colorimetry with dark-field microscopy, integrated into the smartphone microscope platform to detect levels of lead below the safety threshold set by the Environmental Protection Agency.

"Smartphone nano-colorimetryper billion in deionized water.

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Shih and his students last year published an open-source dataset in Biomedical Optics Express, explaining how to convert a smartphone equipped with the elastomer lens into a microscope capable of fluorescence microscopy. That paper has been the journal's most frequently downloaded paper since its publication.

The latest application incorporates color analysis to detect nanoscale lead particles. In addition to Shih, researchers on the project include first author Hoang Nguyen and Yulung Sung, Kelly O'Shaughnessy and Xiaonan Shan, all with the UH Department of Electrical & Computer Engineering. (O'Shaughnessy was a summer intern from the University of Cincinnati under the National Science Foundation's Research Experiences for Undergraduates program.)

Applying the dataset published in 2017, the researchers built a self-contained smartphone microscope that can operate in both fluorescence