Development of a Paper-Based Fluidic Device for Phosphorus Detection

Phosphorus is an essential nutrient for maintaining a healthy ecosystem; however, heightened levels of phosphorus can have negative effects, including algal blooms, which upon decomposition, can lead to oxygen depletion, resulting in regions lacking aquatic life. It is therefore important to monitor phosphorus levels in bodies of water. Current quantitative methods for phosphorus detection in water are based on the standard method 4500-PE, which detects phosphorus colorimetrically through the reduction of an antimony-phosphomolybdate complex. This standard method, however, often requires sample preservation along with a large amount of reagents. In addition, an absorbance spectrophotometer must be employed for sensitive detection. In order to develop a more rapid, low-cost, on-site device for detection, a paper-based fluidic device (PFD) has been developed requiring microliter reagent volumes for detection of phosphorus as phosphate using a modified ascorbic acid reduction method. These PFDs are smaller than a business card, and are fabricated on cellulose filter paper using a wax printer and a hotplate to develop channels for reagent mixing. Upon mixing of phosphate-containing sample and a combined reagent consisting of sulfuric acid, ammonium molybdate, potassium antimonyl tartrate, and ascorbic acid, a blue color develops. The intensity of the blue color is directly related to the phosphorus concentration, which was measured visually or through densitometer software. It has been found that as little as 150 ppb phosphorus can be detected. This method can be applied in the field to detect and possibly pinpoint sources of nutrient loading into a body of water.