Visual quantification of Hg on a microfluidic paper-based analytical device using distance-based detection technique

We presented a distance-based detection method for visual quantification of mercury ions on a microfluidic paper-based analytical device (μPAD). Dithizone in NaOH solution was used as chromogenic reagent and deposited onto paper channel delimited by hydrophobic wax barrier. Reactions happened between mercury ions and dithizone to form an insoluble colored complex, producing colored precipitate on the paper channel. The length of colored precipitate could be readily measured using the printed ruler along each device. The length of precipitate increase linearly with the mercury concentrations, mercury in sample solution could be quantified by measuring the length of the colored precipitate. Being free of any electronic instruments, this method has the advantages of portability, ease of use, low cost and disposability. This presented method was used to detect mercury ions in a synthetic sample, demonstrating its potential in on-site and real time analysis.