Even small amounts of lead can cause serious health problems. U.S. Environmental Protection Agency (EPA) standards require lead levels in drinking water to be below 15 parts per billion. Currently available consumer test kits are not sensitive enough to accurately detect lead at that level. A new system has been developed 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 combines nano-colorimetry with dark-field microscopy, integrated into a smartphone microscope platform, to detect levels of lead below the safety threshold set by the Environmental Protection Agency (EPA). The system has the potential to enable individual citizens to examine (lead) content in drinking water on-demand in virtually any environmental setting.
By using an inexpensive smartphone equipped with an inkjet-printed lens and using the dark-field imaging mode, the system is both portable and easy to operate, as well as able to detect lead concentrations at 5 parts per billion in tap water. The sensitivity reached 1.37 parts per billion in deionized water.
The system incorporates color analysis to detect nanoscale lead particles. The researchers built a self-contained smartphone microscope that can operate in both fluorescence and dark-field imaging modes and paired it with an inexpensive Lumina 640 smartphone with an 8-megapixel camera. They spiked tap water with varying amounts of lead, ranging from 1.37 parts per billion to 175 parts per billion. They then added chromate ions that react with the lead to form lead chromate nanoparticles; the nanoparticles can be detected by combining colorimetric analysis and microscopy.
The analysis measured the intensity detected from the nanoparticles, correlating that to the lead concentration, and verified that the reaction was spurred by the presence of lead. The mixture was transferred to a polydimethylsiloxane slab attached to a glass slide. After it dried, deionized water was used to rinse off the chromate compound and the remaining sediment was imaged for analysis. The microscopy imaging capability proved essential because the quantity of sediment was too small to be imaged with an unassisted smartphone camera, making it impossible to detect relatively low levels of lead.