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Highly sensitive, colorimetric, paper-based devices for the detection of nitrate and nitrite

Reported herein is the development and implementation of paper-based microfluidic devices for the detection of nitrate and nitrite in marine ecosystems. In these environments, high concentrations of nutrients such as nitrate and nitrite lead to unimpeded algal growth and low dissolved oxygen levels; conditions which are deadly for shellfish, fish, and invertebrates. High concentrations of these nutrients are also indicative of ecosystem-wide problems, and occur as a result of water stagnation, as well as through runoff from wastewater treatment plants and agricultural activities. The detection of nitrate and nitrite by rapid and robust colorimetric, paper-based detection schemes that can be used on-site is of high interest to individuals monitoring marine environments, especially if such systems can be used by individuals with limited training. Many detection schemes have already been developed and are commercially available, yet many of them suffer from high detection limits (i.e. relative insensitivity toward target analytes), the use of highly toxic reagents in large quantities, and/or poor selectivity between nitrate and nitrite. Thus, new devices have been developed which allow for the differentiation and dual detection of nitrite and nitrate with detectable concentrations as low as 16 ppb, and that employ variations of the commonly used Griess reagents.