Bromide is an early indicator of water contamination by fracking waste. To detect contamination arising from fracking activity, Vincent Remcho and colleagues, Oregon State University, Corvallis, OR, USA, have developed a microfluidic paper-based analytical device (μPAD) for the quantitative colorimetric detection of bromide in water.

The device is inexpensive to fabricate, robust, easy-to-use, portable, has smartphone-enabled data collection, and does not use wet reagents. It consists of three layers of filter paper containing bromide-specific colorimetric reagents. Chloramine T in the bottom sheet oxidizes bromide. This leads to bromination of phenol red in the middle sheet. The top sheet contains a buffer. Applying a bromide containing water sample from the top leads to a color change from yellow to blue which is detected from the bottom.

The color change is proportional to the concentration of bromide. A detection limit of 3.218 ppm bromide was reached. The assay is specific for bromide, even in the presence of high concentrations of chloride and iodide. Future work will focus on improving the detection limit.

• Detection of water contamination from hydraulic fracturing wastewater: a μPAD for bromide analysis in natural waters,
  Leslie J. Loh, Gayan C. Bandara, Genevieve L. Weber, Vincent T. Remcho,
  Analyst 2015, 140, 5501–5507.
  DOI: 10.1039/c5an00807g